Actin represents one of the most abundant, evolutionarily conserved, and functionally versatile proteins across eukaryotic life, serving as the foundational building block for the microfilament system. Far from functioning merely as a static scaffolding element, actin undergoes rapid, regulated transitions between monomeric and polymeric states to orchestrate cell motility, structural morphogenesis, and force generation. Understanding the biochemical and biophysical mechanisms of actin offers indispensable insights into cellular physiology, muscular contraction, developmental biology, and a broad spectrum of human pathologies.
Actin
1. Concise Definition
Actin is a highly conserved, 42-kilodalton globular structural protein found abundantly in eukaryotic cells that polymerizes to form linear helical microfilaments. These microfilaments constitute an essential component of the cytoskeleton, providing mechanical support, maintaining cellular geometry, and generating intracellular tensile force.
In its native physiological environments, actin exists in a dynamic equilibrium between two principal states: monomeric globular actin (G-actin) and filamentous polymeric actin (F-actin). Driven by adenosine triphosphate (ATP) binding and subsequent hydrolysis, actin filaments assemble with an intrinsic structural polarity, establishing structurally distinct barbed (plus) and pointed (minus) ends. This polarity enables asymmetric kinetic behavior, including the phenomenon of filament treadmilling, wherein monomer addition at the barbed end balances subunit dissociation at the pointed end.
Beyond its conventional structural role, actin functions as an active participant in mechanotransduction, endocytosis, cytokinesis, organellar transport, and intracellular signaling cascades. Through tight association with a repertoire of over one hundred actin-binding proteins (ABPs) and motor enzymes such as myosin, actin converts chemical energy directly into mechanical work, making it the primary motor substrate driving both non-muscle cell movement and macroscopic voluntary muscular contraction.
2. Etymology & Linguistic Origin
The term actin originates from the Ancient Greek root aktīs (ἀκτίς, genitive ἀκτῖνος, aktinos), signifying a “ray,” “beam,” or “radiating spike.” This morphological nomenclature was historically derived from the appearance of the filamentous protein networks and their directional, ray-like organization observed within muscle tissue and isolated protein preparations.
The designation was formally coined in 1942 by the Hungarian biochemist Brunó Ferenc Straub while conducting research in the laboratory of Albert Szent-Györgyi at the University of Szeged. Straub isolated a novel protein that, when combined with previously purified myosin, drastically increased the viscosity of the solution and conferred contractility upon the addition of ATP. Because this newly discovered factor actively “activated” the contractile response of myosin, the Greek root was also semantically aligned with the concept of activation and physical radiance, entering international scientific nomenclature as actin in English, aktin in German, and actine in French.
3. Pronunciation & Grammatical Form
In standard scientific English, actin is pronounced phonetically as /ˈæk.tɪn/ (AK-tin). Grammatically, it functions as an uncountable, concrete noun within biochemistry, cell biology, and biophysics. When referencing distinct biological isoforms or molecular variations, it may occasionally be pluralized as actins (e.g., “the differential expression of cardiac and smooth muscle actins”).
Attributively, actin frequently modifies nouns to denote anatomical or biochemical features, generating standard compound terminology such as actin filament, actin monomer, actin cortex, actin dynamics, and actin-binding protein. Derived adjectival formations include actomyosin (characterizing the complex of actin and myosin), actinic (rarely used in cell biology to avoid confusion with photochemistry), and actin-dependent.
4. Detailed Conceptual Explanation
At the structural level, actin is composed of 375 amino acid residues in typical mammalian isoforms, folding into an asymmetric, four-domain macromolecule bisected by a profound nucleotide-binding cleft. This central cleft coordinates a divalent cation (predominantly magnesium, Mg²⁺, under physiological conditions, or calcium, Ca²⁺, in in vitro preparations) alongside an adenine nucleotide, specifically ATP or adenosine diphosphate (ADP). The spatial configuration divides the monomer into two major halves, traditionally referred to as Subdomains 1 and 2 on the outer periphery and Subdomains 3 and 4 across the cleft, which exhibit subtle hinge-bending motions that dictate polymerization competence.
The biological functionality of actin hinges on the continuous, non-equilibrium cycle of polymerization into microfilaments. G-actin monomers spontaneously nucleate into unstable dimers and trimers—the rate-limiting step of polymerization—before rapidly elongating into two parallel, right-handed protofilaments that wind around one another to construct a polar, double-helical cable approximately 7 to 9 nanometers in diameter. The intrinsic polarity results from the uniform orientation of all constituent subunits within the filament: Subdomains 1 and 3 point toward the barbed (+) end, whereas Subdomains 2 and 4 are oriented toward the pointed (−) end.
This structural polarity is intimately linked to the thermodynamics of nucleotide hydrolysis. ATP-bound G-actin incorporates at the barbed end at a rate near the diffusion-controlled limit (association rate constant k_on ≈ 12 µM⁻¹s⁻¹), exhibiting a low critical concentration (Cc ≈ 0.1 µM). Shortly after subunit incorporation, the intrinsic ATPase activity of actin is stimulated by several orders of magnitude, converting bound ATP into ADP-Pi (an intermediate state with delayed phosphate release), and eventually into ADP-actin. ADP-actin has a markedly higher dissociation rate and a significantly elevated critical concentration at the pointed end (Cc ≈ 0.6–0.8 µM). Consequently, at steady-state monomer concentrations intermediate between these two thresholds, net polymerization occurs at the barbed end while equivalent depolymerization occurs at the pointed end, maintaining steady filament length through persistent energy consumption—a process termed steady-state treadmilling.
Within the living cytoplasm, this dynamic equilibrium is governed by a dedicated network of actin-binding proteins. Monomer-sequestering proteins like profilin and thymosin-β4 maintain an abundant soluble reservoir of G-actin while preventing spontaneous, unregulated nucleation. Nucleation-promoting factors such as the Wiskott-Aldrich syndrome protein (WASP) activate the Actin-Related Protein 2/3 (Arp2/3) complex to induce branched filament networks, characteristic of lamellipodia. Conversely, formins associate processively with the barbed end to catalyze unbranched, parallel bundles found in stress fibers and contractile rings. Filament turnover is accelerated by actin-depolymerizing factor (ADF)/cofilin, which binds preferentially to ADP-actin, alters filament helical twist, induces mechanical severance, and promotes pointed-end dissociation to recycle monomers back into the assembly cycle.
5. Historical Development
The discovery and conceptualization of actin emerged from mid-twentieth-century attempts to resolve the fundamental biochemistry of muscular contraction. Prior to the 1940s, physiology assumed that muscle contraction was driven by a single protein termed “myosin,” as described by Willy Kühne in the nineteenth century. However, this classical view could not adequately explain why different preparations of myosin yielded radically divergent physical and enzymatic responses to ATP.
Between 1941 and 1943, operating under wartime scarcity at the University of Szeged, Albert Szent-Györgyi and his young associate Brunó Ferenc Straub systematically decomposed muscle extracts. Straub established that the previously characterized “myosin” was in fact a complex of two distinct entities: a genuine motor protein, which retained the name myosin, and a distinct, extractable component that Straub isolated using an acetone powder extraction technique and christened “actin.” In their seminal publications, the Szeged group demonstrated that actin exists as both a monomeric solute and an aggregated polymer, and that the combined “actomyosin” gel underwent precipitous syneresis (contraction) when exposed to ATP and physiological salts.
During the 1950s and 1960s, the emergence of transmission electron microscopy and X-ray diffraction transformed the understanding of actin from an isolated biochemical entity to a defined macromolecular structure. Hugh Huxley and Jean Hanson, alongside Andrew Huxley and Rolf Niedergerke, formulated the sliding filament theory in 1954, positioning actin filaments as the primary constituents of the I-bands (isotropic thin filaments) that physically slide past the thick myosin filaments of the A-band without altering their intrinsic length.
In the late 1960s and 1970s, pioneering work by Thomas Pollard, Mark Mooseker, and Edward Korn revealed that actin was not confined to muscle tissue, establishing its ubiquitous presence across all eukaryotic cell types. The molecular structure of actin was definitively resolved at atomic resolution in 1990 by Wolfgang Kabsch, Kenneth Holmes, and colleagues, who crystallized G-actin in complex with the protein DNase I. This breakthrough was followed by Ken Holmes’s filament models and modern high-resolution cryo-electron microscopy reconstructions, which collectively unveiled the atomic details of actin filament plasticity, ATP hydrolysis, and inter-subunit interfaces.
6. Theoretical Foundations
The theoretical frameworks governing actin biology span physical chemistry, non-equilibrium thermodynamics, and cellular biomechanics. Central to actin biophysics is the classical nucleation-elongation theory formalized by Fumio Oosawa and Shin-ichi Asakura in the 1960s. Under this theoretical paradigm, actin polymerization is treated as a condensation phenomenon analogous to a phase transition, characterized by a distinct critical concentration below which monomers remain strictly dispersed, and above which any excess monomer is quantitatively converted into polymer.
Furthermore, actin filaments provide the primary experimental model for non-equilibrium steady states in biological systems. Unlike passive polymers governed by equilibrium thermodynamics, actin dynamics are fueled by continuous ATP dissipation. The theory of treadmilling, formulated mathematically by Albert Wegner in 1976, demonstrates that nucleotide hydrolysis breaks microscopic reversibility, permitting continuous directional flux along the filament coordinate without requiring structural disruption of the macroscopic polymer network.
From a mechanical perspective, actin architectures are conceptualized through the lens of cellular tensegrity, a biomechanical theory popularized by Donald Ingber. This paradigm posits that cells stabilize their three-dimensional structure not via fluid-filled hydrostatic compression alone, but through an integrated network of tensed contractile actomyosin cables (tension elements) working against compressed microtubules and extracellular adhesion sites (compression elements). Concurrently, continuum mechanics models treat the cortical actin meshwork as an active viscoelastic gel, wherein local remodeling, crosslinking density, and myosin-driven active stresses determine whole-cell surface tension, cortex elasticity, and viscous dissipation during cell division and crawling.
7. Key Components, Types & Dimensions
Actin exhibits diverse structural subdivisions, evolutionary isoforms, and functional configurations:
- Molecular Isoforms: In birds and mammals, six distinct actin genes encode three major classes differing by only a few amino acid substitutions in their N-termini:
- Alpha-actins (α-skeletal, α-cardiac, α-smooth muscle): Specialized for high-tensile, long-term contractile stability within striated and visceral muscle tissue.
- Beta-actin (β-cytoplasmic): Ubiquitous non-muscle isoform oriented toward leading-edge motility, endocytosis, and asymmetric intracellular protein synthesis.
- Gamma-actins (γ-cytoplasmic, γ-smooth muscle): Involved in structural tension, auditory hair cell stereocilia stability, and enteric tract contraction.
- Monomeric Subdomains: G-actin comprises four structural subdomains organized around a central catalytic pocket:
- Subdomain 1 (Residues 1–32, 70–144, 338–375): Contains both the N- and C-termini, presenting major binding interfaces for myosin, cofilin, and alpha-actinin.
- Subdomain 2 (Residues 33–69): The smallest, most flexible subdomain; incorporates the D-loop, which mediates critical longitudinal contacts within the F-actin filament.
- Subdomain 3 (Residues 145–179, 270–337): Structurally resembles Subdomain 1; coordinates the nucleotide and participates in lateral inter-strand filament interactions.
- Subdomain 4 (Residues 180–269): Forms the upper internal wall of the nucleotide cleft, directly coupling nucleotide hydrolysis states to overall monomer conformation.
- Supramolecular Architectures: In vivo assemblies defined by accessory actin-binding proteins:
- Dendritic Networks: Highly branched arrays organized by Arp2/3 at a stereotypic 70-degree angle, generating pushing forces at the leading edge of migrating cells.
- Parallel Bundles: Tightly packed, uniformly polarized filaments crosslinked by fascin or fimbrin, generating rigid protrusions such as filopodia, microvilli, and stereocilia.
- Antiparallel Contractile Arrays: Mixed-polarity filament bundles crosslinked by alpha-actinin and interspersed with myosin II motors, forming stress fibers and the cytokinetic contractile ring.
- Cortical Meshworks: An isotropic, dense two-dimensional sheet localized immediately beneath the plasma membrane, crosslinked by spectrin and filamin to resist shear stress.
8. Examples & Illustrative Cases
The operational versatility of actin can be illustrated through distinct physiological paradigms occurring across different spatial and temporal scales.
A prime example is fibroblast chemotactic migration during dermal wound healing. Upon sensing a gradient of platelet-derived growth factor, signaling cascades via the Rho-family GTPase Rac1 stimulate the Arp2/3 complex at the front of the cell. This triggers explosive actin polymerization against the inner surface of the plasma membrane, driving the formation of a broad, flattened cellular protrusion known as a lamellipodium. As the leading edge advances, actin filaments attach to the extracellular matrix through integrin-based focal adhesions. Concurrently, RhoA activation at the cell rear stimulates non-muscle myosin II contraction along antiparallel actin stress fibers, generating pulling forces that retract the trailing edge and propel the cell forward.
A second case is the contractile ring during animal cell cytokinesis. Following the segregation of sister chromatids during anaphase, an equatorial zone of active RhoA recruits formins and myosin II motors to assemble a transient, circumferentially oriented actomyosin ring beneath the cleavage furrow. As myosin II filaments walk toward the barbed ends of opposing actin filaments, the ring constricts in a purse-string fashion, pulling the plasma membrane inward until it pinches the parental cell into two genetically identical daughter cells, followed by ESCRT-mediated abscission.
A third clinical case involves pathogen-hijacked actin rocketing. Intracellular bacterial pathogens such as Listeria monocytogenes and Shigella flexneri exploit the host cell’s actin machinery to move between cells without exposing themselves to extracellular immune surveillance. Listeria expresses a surface protein called ActA at one pole of its outer membrane, which structurally mimics endogenous host nucleation-promoting factors. ActA binds and activates the host Arp2/3 complex, nucleating a dense “comet tail” of actin filaments directly behind the bacterium. The continuous polymerization of this actin tail produces sufficient propulsive force to drive the bacterium through the viscous cytoplasm at speeds reaching 1.5 micrometers per second, ultimately forming plasma membrane protrusions that are engulfed by adjacent neighboring cells.
9. Measurement & Assessment
Investigating actin assembly, structure, and dynamics requires specialized biochemical and biophysical methodologies that probe both bulk behavior and single-molecule mechanics.
In classical biochemistry, filament assembly and disassembly kinetics are monitored via pyrene-actin fluorescence spectroscopy. Monomeric actin is covalently tagged at Cysteine-374 with N-(1-pyrenyl)iodoacetamide. When pyrene-actin incorporates into an actin filament, its fluorescence quantum yield increases by roughly twenty-fold. By tracking fluorescence emission over time, researchers can quantify initial nucleation rates, elongation velocity, and equilibrium critical concentrations under variable buffer conditions.
To study structural assemblies in fixed or live biological specimens, specific molecular probes are employed:
- Fluorescent Phalloidin Derivatives: Phalloidin, a bicyclic heptapeptide toxin derived from the death cap mushroom (Amanita phalloides), binds with nanomolar affinity specifically to the interface between three adjacent subunits in F-actin without recognizing G-actin. Conjugated to fluorophores, it represents the gold standard for high-resolution confocal visualization of the filamentous cytoskeleton in fixed cells.
- Genetically Encoded Live-Cell Markers: Fluorescent protein fusions such as Lifeact (a 17-amino-acid peptide derived from yeast ABP140), Utrophin-CH domain, and F-tractin permit non-disruptive, real-time tracking of actin remodeling in living tissues without perturbing native assembly dynamics.
- Total Internal Reflection Fluorescence (TIRF) Microscopy: Single-molecule in vitro TIRF assays allow direct observation of individual actin filaments polymerizing on functionalized coverslips in real time, revealing parameters such as subunit addition rates, branching kinetics by Arp2/3, and filament severing by cofilin.
- Sedimentation and Viscometry Assays: High-speed ultracentrifugation (typically 100,000 × g) quantitatively pellets heavy F-actin polymers while leaving monomeric G-actin in the supernatant, allowing determination of the polymeric-to-monomeric ratio across cell lysates via subsequent Western blotting.
10. Applications & Practical Significance
Because actin dynamics sit at the nexus of cellular architecture and physiological function, translational research targeting the actin system carries profound implications for medicine, biotechnology, and pharmacology.
In oncology, aberrant actin remodeling is a universal hallmark of malignant transformation. Cancer cells hijack actin-regulatory pathways to downregulate intercellular adherence junctions, undergo epithelial-mesenchymal transition (EMT), and form actin-rich, matrix-degrading protrusions termed invadopodia. Consequently, pharmacological agents targeting actin regulators—such as small-molecule inhibitors of LIM kinase, Arp2/3, or the upstream GTPases Rho and Rac—are actively investigated as anti-metastatic therapeutics designed to freeze cancer dissemination.
In cardiovascular medicine, mutations in the genes encoding human cardiac alpha-actin (ACTC1) or smooth muscle alpha-actin (ACTA2) cause severe hereditary diseases. Point mutations in ACTC1 destabilize sarcomere force transmission, precipitating familial hypertrophic cardiomyopathy (HCM) or dilated cardiomyopathy (DCM), often culminating in early heart failure or sudden cardiac death. Pathogenic variants in ACTA2 cause thoracic aortic aneurysms and dissections (TAAD), underscoring the critical role of vascular actin in withstanding pulsatile hemodynamic shear stress.
In pharmacology and natural products research, actin is targeted by an array of secondary metabolites produced by marine invertebrates, fungi, and plants as defensive toxins. Cytochalasins (fungal metabolites) cap filament barbed ends and inhibit polymerization, whereas latrunculins (sponge-derived macrolides) sequester G-actin monomers, driving rapid filament disassembly. Conversely, jasplakinolide stabilizes actin filaments and promotes disordered polymerization. These small molecules serve as indispensable research reagents to systematically interrogate cytoskeletal dependencies in biological systems.
11. Research & Empirical Evidence
Decades of rigorous empirical investigation have delineated the precise chemical and mechanical rules governing actin networks. Landmark studies conducted by Thomas Pollard and John Cooper in the 1980s quantified the association and dissociation rate constants for both barbed and pointed filament ends, establishing the physical basis of actin treadmilling and cementing the concept of filament polarity.
Modern biophysical investigations using optical tweezers and atomic force microscopy (AFM) have quantified the mechanical properties of single actin filaments. Measurements indicate that actin filaments exhibit a persistence length (L_p) of approximately 10 to 17 micrometers—comparable to the physical dimensions of an animal cell—classifying them as semiflexible polymers. Under excessive mechanical strain, single filaments demonstrate a flexural rigidity that permits them to resist tensile loads on the order of hundreds of piconewtons before undergoing structural rupture.
In recent years, structural biology has leveraged advances in cryo-electron microscopy (cryo-EM) to elucidate actin filaments at near-atomic resolution (sub-3.0 Å). Landmark studies by Julian von der Ecken, Stefan Raunser, and colleagues have visually captured the precise structural rearrangements that occur within the nucleotide cleft during the transition from G- to F-actin, pinpointing the active catalytic residues that orient the nucleophilic water molecule responsible for ATP cleavage. Furthermore, structural studies have revealed how distinct actin-binding proteins recognize subtle, cooperative conformational changes across the filament lattice, explaining how binding by one factor can propagate allosteric changes along the entire length of a microfilament.
12. Cultural & Cross-Cultural Considerations
Within the context of academic nomenclature, taxonomy, and evolutionary biology, actin exhibits exceptional cross-species conservation that crosses vast phylogenetic distances. The amino acid sequence of actin is extraordinarily conserved across kingdoms; human cytoplasmic beta-actin shares over 90% identity with actin from the baker’s yeast Saccharomyces cerevisiae, and more than 85% identity with actin from the amoebozoan Dictyostelium discoideum. This extreme conservation indicates that virtually every surface residue on the actin monomer participates in essential inter-subunit interactions or contacts with indispensable actin-binding proteins, leaving minimal evolutionary tolerance for non-synonymous mutations.
Beyond eukaryotic biology, comparative genomics has identified prokaryotic ancestors and structural homologs of actin, redefining our understanding of bacterial cell biology. Bacterial proteins such as MreB, ParM, and FtsA possess structural folds—the actin-like ATPase fold—that are virtually identical to eukaryotic actin, despite exhibiting limited primary amino acid sequence homology. In bacteria, these filaments control peptidoglycan cell-wall synthesis, segregate low-copy plasmids, and anchor division machinery. The cross-cultural and international consensus regarding actin nomenclature has enabled unified, standardized research efforts, ensuring that structural coordinates cataloged in international repositories such as the Protein Data Bank (PDB) are universally applied across global biological and medical sciences.
13. Criticisms, Debates & Limitations
Despite its central position in cell biology, several aspects of actin structure and regulation remain areas of intense debate and conceptual revision.
One enduring controversy centers on nuclear actin. Historically, actin was considered exclusively cytoplasmic; observations of actin inside the nucleus were frequently dismissed as biochemical contamination or non-specific staining artifacts. However, contemporary research has demonstrated that actin is actively transported into the nuclear compartment, where it participates in chromatin remodeling complexes, interacts with RNA polymerases I, II, and III, and facilitates the spatial organization of the genome. Debates persist regarding the physical state of nuclear actin: while some investigators present evidence for conventional F-actin filaments driving nuclear structure and DNA damage repair, others argue that nuclear actin functions primarily as unconventional monomers, short oligomers, or specialized non-canonical polymers that resist detection by traditional probes such as phalloidin.
Another active debate involves the mechanochemical plasticity of the actin filament. For decades, the actin filament was modeled as an invariant, uniform cable. Emerging evidence suggests the F-actin lattice is fundamentally polymorphic, capable of adopting distinct structural states characterized by variable helical pitch and mechanical flexibility depending on nucleotide state, applied mechanical tension, and the binding of specific crosslinkers. The debate centers on whether these structural transitions represent genuine biological regulatory switches that govern accessory protein recruitment, or whether they simply reflect thermal fluctuations and stochastic noise intrinsic to flexible protein polymers.
Finally, researchers frequently encounter limitations when translating in vitro reconstitution assays to native in vivo cellular physiology. Purified actin in a buffer exhibits predictable treadmilling and assembly kinetics; however, inside the living cytoplasm, macromolecular crowding (where proteins occupy over 30% of total volume), severe monomer competition, localized pH gradients, and spatial confinement create complex emergent behaviors that frequently diverge from predictions derived from dilute solution biochemistry.
14. Related Terms & Distinctions
To prevent conceptual ambiguity, actin must be clearly distinguished from other major cytoskeletal and structural proteins:
- Actin vs. Myosin: Actin is the track-forming structural filament that provides architectural scaffolding, whereas myosin is a superfamily of ATP-dependent molecular motor proteins that physically bind to actin filaments and convert chemical energy into mechanical force to drive contraction or vesicular transport.
- Actin vs. Tubulin: While both are dynamic, nucleotide-binding cytoskeletal polymers, tubulin is a GTP-binding heterodimer (α/β-tubulin) that polymerizes into rigid, hollow cylinders (microtubules, ~25 nm diameter) utilized primarily for chromosome segregation and long-distance trafficking, in contrast to the thinner, flexible, ATP-driven helical actin microfilaments (~7 nm diameter).
- Actin vs. Intermediate Filaments: Unlike actin microfilaments and microtubules, intermediate filaments (e.g., keratins, vimentin, lamins) are non-polar, do not bind or hydrolyze nucleotides (ATP/GTP), and assemble into tough, elastic fibers primarily dedicated to resisting passive mechanical stress rather than facilitating active dynamic motility.
- G-Actin vs. F-Actin: G-actin refers explicitly to the single, unpolymerized globular monomer (~42 kDa), whereas F-actin refers to the assembled, polar, multi-subunit filamentous polymer.
15. Summary / Key Takeaways
Actin is a central structural and mechanical protein of the eukaryotic cell. Assembling from 42-kilodalton globular monomers (G-actin) into polar, dynamic microfilaments (F-actin), it harnesses ATP binding and hydrolysis to drive continuous filament remodeling via treadmilling. Orchestrated by a vast array of specialized actin-binding proteins, actin builds structures ranging from branched leading-edge lamellipodia and rigid filopodia to muscle sarcomeres and cytokinetic contractile rings.
Beyond its classic structural role, actin functions as a dynamic mechanical transducer and signaling hub. The profound evolutionary conservation of its structure—and the presence of related homologs across the bacterial domain—underscores its essential role in maintaining cellular life. Ongoing investigations into its nuclear roles, lattice mechanics, and involvement in oncogenesis continue to uncover new facets of this essential biological macromolecule.
In conclusion, actin represents much more than a passive internal skeleton; it is an active, self-assembling motor substrate and mechanical engine that governs the shape, movement, and division of eukaryotic cells. From the subtle crawling of embryonic fibroblasts to the forceful beating of the mammalian heart, the dynamic transitions between G-actin and F-actin form the fundamental biophysical foundation for life in motion.
References
- Holmes, K. C., Popp, D., Gebhard, W., & Kabsch, W. (1990). Atomic model of the actin filament. Nature, 347(6288), 44–49. https://doi.org/10.1038/347044a0
- Huxley, H., & Hanson, J. (1954). Changes in the cross-striations of muscle during contraction and stretch and their structural interpretation. Nature, 173(4412), 973–976. https://doi.org/10.1038/173973a0
- Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F., & Holmes, K. C. (1990). Atomic structure of the actin: DNase I complex. Nature, 347(6288), 37–44. https://doi.org/10.1038/347037a0
- Pollard, T. D., & Cooper, J. A. (2009). Actin, a central player in cell shape and movement. Science, 326(5957), 1208–1212. https://doi.org/10.1126/science.1175862
- Straub, F. B. (1942). Actin. Studies from the Institute of Medical Chemistry University Szeged, 2, 3–15.
- Wegner, A. (1976). Head to tail polymerization of actin. Journal of Molecular Biology, 108(1), 139–150. https://doi.org/10.1016/S0022-2836(76)80102-1