PDBsum entry 1m4j

Structural protein

PDB id

1m4j

Contents

			Protein chains

					133 a.a. *

			Waters ×107

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Structural conservation between the actin monomer-Binding sites of twinfilin and actin-Depolymerizing factor (adf)/cofilin.

Authors

V.O.Paavilainen, M.C.Merckel, S.Falck, P.J.Ojala, E.Pohl, M.Wilmanns, P.Lappalainen.

Ref.

J Biol Chem, 2002, 277, 43089-43095. [DOI no: 10.1074/jbc.M208225200]

PubMed id

12207032

Abstract

Twinfilin is an evolutionarily conserved actin monomer-binding protein that regulates cytoskeletal dynamics in organisms from yeast to mammals. It is composed of two actin-depolymerization factor homology (ADF-H) domains that show approximately 20% sequence identity to ADF/cofilin proteins. In contrast to ADF/cofilins, which bind both G-actin and F-actin and promote filament depolymerization, twinfilin interacts only with G-actin. To elucidate the molecular mechanisms of twinfilin-actin monomer interaction, we determined the crystal structure of the N-terminal ADF-H domain of twinfilin and mapped its actin-binding site by site-directed mutagenesis. This domain has similar overall structure to ADF/cofilins, and the regions important for actin monomer binding in ADF/cofilins are especially well conserved in twinfilin. Mutagenesis studies show that the N-terminal ADF-H domain of twinfilin and ADF/cofilins also interact with actin monomers through similar interfaces, although the binding surface is slightly extended in twinfilin. In contrast, the regions important for actin-filament interactions in ADF/cofilins are structurally different in twinfilin. This explains the differences in actin-interactions (monomer versus filament binding) between twinfilin and ADF/cofilins. Taken together, our data show that the ADF-H domain is a structurally conserved actin-binding motif and that relatively small structural differences at the actin interfaces of this domain are responsible for the functional variation between the different classes of ADF-H domain proteins.



	Figure 1. Fig. 1. Structure of the N-terminal ADF-H domain of mouse twinfilin. A, a schematic ribbon diagram of the N-terminal ADF-H domain of twinfilin, Twf[1-142]. The structure is color-ramped from blue (N terminus) via green to red (C terminus). B, a representative section of the 2F[o] F[c] 1.6-Å electron density map contoured at 1 centered around residue Asp-74. C, C[ ]superimposition of Twf[1-142] (red) and yeast cofilin (blue). Twf[1-142] is in the same orientation as in panel A. The strands 3 and 4 (red arrow) and the C-terminal helix 4 (blue arrow) are oriented differently in Twf[1-142] and ADF/cofilins. The superposition was produced with DALI (41).		Figure 5. Fig. 5. Comparison of the actin-binding sites of the N-terminal ADF-H domain of twinfilin, cofilin, and gelsolin. A, ribbon diagrams of mouse Twf[1-142], yeast cofilin and human gelsolin segment-1. The side chains of the residues important for actin monomer binding in these proteins are indicated by red. The side chains of the cofilin residues important for F-actin binding are indicated by blue, and the twinfilin residues mutated in this study that do not contribute to actin binding are indicated by green. The gelsolin segment-1 residues important for G-actin interaction are taken from the segment-1 actin monomer co-crystal structure (43), and the cofilin residues important for G- and F-actin interactions are taken from (32-34, 42, 44, 45). The twinfilin residues mutated in this study are indicated by letters and numbers. B, electrostatic surface potential of the actin-binding sites of Twf[1-142], yeast cofilin, and gelsolin segment-1 displayed at ± 10 kT/e^ . The orientation of the proteins is identical to panel A, and the actin monomer-binding surfaces are circled by orange dashed lines. Regions of positive and negative potential are blue and red, respectively. The surface potentials of the actin monomer-binding sites of Twf[1-142] and yeast cofilin are similar to each other, whereas this site on gelsolin segment-1 is more strongly and uniformly negatively charged. This figure was prepared with GRASP (46).