Actin monomer illustration

Fig. 8. Illustration of the actin monomer structure solved by X-ray crystallography (Kabsch et al, 1990) showing the four structural subdomains of the actin monomer, labeled, in the front (A) and back (B) view with N, C-termini labeled 1-4. Also labeled is the loop linking residues 262 and 309 between subdomains 3 and 4.

Fig. 9. Representation of a 13/6 actin filament together with its illustration by means of a radial net. In (A) an imaginary piece of paper is wrapped round the filament and on it are marked all the positions of the actin monomers. The paper is then unwrapped as in (B) and the helical tracks in (A) become straight lines. The final result in (C) is the radial projection or radial net. The 59 A pitch length (P) and 27.5 A subunit axial translation (h) are indicated in (C).

Figure 9 Illustration of sliding movements of F-actin on fixed myosin coupled with the ATP hydrolysis the conformation of actin monomers during and after interaction with myosin may be changing.

Table I illustrates the variability of the amino-terminal residues of several different actin isoforms. Mutagenesis in this region can result in partial or complete inhibition of F-actin motility (Sutoh, 1993), consistent with the site being a likely initial target for myosin during the cross-bridge cycle (Rayment et al., 1993b). In fact, numerous studies also have identified several domains of the actin molecule representing clusters of amino acids specifically involved in monomer-monomer interactions (Holmes et al., 1990 Hennessey et al., 1993 Khaitlina et al., 1993 Labbe et al., 1994), actin-myosin interactions (Holmes and Kabsch, 1991 Hennessey et al., 1993 Schroder et al.,...

Figure 2 (a) A two-strand helical polymer structure of F-actin. (b) and (c) Illustration of hypothetical conformational changes of F-actin caused by weakening of the monomer-monomer bond possibly coupled with the ATP hydrolysis cycle. 

When we reached the idea of helical polymerization, we imagined immediately that the partial breaking or weakening of monomer-monomer bonds may produce a large conformational change of F-actin, keeping its filamentous continuity, as illustrated in Fig. 2 [12, 13], Since then, we have been very interested in dynamic behaviors of helical polymers. 

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