High-resolution cryo-EM structure of the F-actin-fimbrin/plastin ABD2 complex

• Published in: Proceedings of the National Academy of Sciences - PNAS 2008-02, Vol.105 (5), p.1494-1498
• Main Authors: Galkin, Vitold E, Orlova, Albina, Cherepanova, Olga, Lebart, Marie-Christine, Egelman, Edward H
• Format: Article
• Language: English
• Subjects: Actins; Actins - chemistry; Atomic interactions; Binding sites; Biochemistry; Biochemistry, Molecular Biology; Biological Sciences; Biopolymers; Cryoelectron Microscopy; Crystal structure; Crystals; Cytoskeleton; Humans; Life Sciences; Membrane Glycoproteins; Membrane Glycoproteins - chemistry; Microfilament Proteins; Microfilament Proteins - chemistry; Microfilaments; Nucleotides; Phosphoproteins; Phosphoproteins - chemistry; Pixels; Protein Conformation; Protein Structure, Tertiary; Protein subunits; Proteins; Yeasts
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0708667105

Many actin binding proteins have a modular architecture, and calponin-homology (CH) domains are one such structurally conserved module found in numerous proteins that interact with F-actin. The manner in which CH-domains bind F-actin has been controversial. Using cryo-EM and a single-particle approach to helical reconstruction, we have generated 12-Å-resolution maps of F-actin alone and F-actin decorated with a fragment of human fimbrin (L-plastin) containing tandem CH-domains. The high resolution allows an unambiguous fit of the crystal structure of fimbrin into the map. The interaction between fimbrin ABD2 (actin binding domain 2) and F-actin is different from any interaction previously observed or proposed for tandem CH-domain proteins, showing that the structural conservation of the CH-domains does not lead to a conserved mode of interaction with F-actin. Both the stapling of adjacent actin protomers and the additional closure of the nucleotide binding cleft in F-actin when the fimbrin fragment binds may explain how fimbrin can stabilize actin filaments. A mechanism is proposed where ABD1 of fimbrin becomes activated for binding a second actin filament after ABD2 is bound to a first filament, and this can explain how mutations of residues buried in the interface between ABD2 and ABD1 can rescue temperature-sensitive defects in actin.