Abstract
Depolymerization and polymerization of the actin filament are indispensable in eukaryotes. The DNase I binding loop (D-loop), which forms part of the interface between the subunits in the actin filament, is an intrinsically disordered loop with a large degree of conformational freedom. Introduction of the double mutation G42A/G46A to the D-loop of the beta cytoskeletal mammalian actin restricted D-loop conformational freedom, whereas changes to the critical concentration were not large, and no major structural changes were observed. Polymerization and depolymerization rates at both ends of the filament were reduced, and cofilin binding was inhibited by the double mutation. These results indicate that the two glycines at the tip of the D-loop are important for actin dynamics, most likely by contributing to the large degree of conformational freedom.
Highlights
Actin is an abundant protein in eukaryotes that forms a double-stranded filament. α-Skeletal and β-cytoplasmic actins from mammals share 100% identical sequences with birds and reptiles, indicating the importance of actin in the cell
Construction of a G42A/G46A mutant model based on the current actin subunit–subunit interaction structure (PDB ID: 6KP8 (Takeda et al, submitted)) revealed that the alanine side chains did not clash with other regions of the actin subunits (Figure 1h)
The current results suggest that the large conformational space sampled by the DNase I binding loop (D-loop) apart from ATPase contributes to the speed of actin dynamics
Summary
Actin is an abundant protein in eukaryotes that forms a double-stranded filament. α-Skeletal and β-cytoplasmic actins from mammals share 100% identical sequences with birds and reptiles, indicating the importance of actin in the cell. Actin is an abundant protein in eukaryotes that forms a double-stranded filament. Α-Skeletal and β-cytoplasmic actins from mammals share 100% identical sequences with birds and reptiles, indicating the importance of actin in the cell. Actin plays central roles in a wide range of cellular functions, including cell motility, the cytoskeleton, cell division and muscle contraction [1]. Actin dynamics through depolymerization and polymerization are indispensable. The monomeric state (G-form) and fibril state (F-form) of actin differ substantially in structure [2]. Actin contains two large rigid bodies [2,3]. There are two prominent structural differences between the G-form and F-form of actin. One is the relative orientation between the two rigid bodies and the other is the conformational change to the DNase I binding loop (D-loop) [4] (Figure 1e)
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