The crystal structure of the C-terminus of adseverin reveals the actin-binding interface.
Adseverin is a member of the calcium-regulated gelsolin superfamily of actin severing and capping proteins. Adseverin comprises 6 homologous domains (A1-A6), which share 60% identity with the 6 domains from gelsolin (G1-G6). Adseverin is truncated in comparison to gelsolin, lacking the C-terminal extension that masks the F-actin binding site in calcium-free gelsolin. Biochemical assays have indicated differences in the interaction of the C-terminal halves of adseverin and gelsolin with actin. Gelsolin contacts actin through a major site on G4 and a minor site on G6, whereas adseverin uses a site on A5. Here, we present the X-ray structure of the activated C-terminal half of adseverin (A4-A6). This structure is highly similar to that of the activated form of the C-terminal half of gelsolin (G4-G6), both in arrangement of domains and in the 3 bound calcium ions. Comparative analysis of the actin-binding surfaces observed in the G4-G6/actin structure suggests that adseverin in this conformation will also be able to interact with actin through A4 and A6, whereas the A5 surface is obscured. A single residue mutation in A4-A6 located at the predicted A4/actin interface completely abrogates actin sequestration. A model of calcium-free adseverin, constructed from the structure of gelsolin, predicts that in the absence of a gelsolin-like C-terminal extension the interaction between A2 and A6 provides the steric inhibition to prevent interaction with F-actin. We propose that calcium binding to the N terminus of adseverin dominates the activation process to expose the F-actin binding site on A2.
Chumnarnsilpa
Sakesit
S
Institute of Molecular and Cell Biology, Agency for Science, Technology, and Research (ASTAR), 61 Biopolis Drive, Proteos, Singapore 138673.
Lee
Wei Lin
WL
Nag
Shalini
S
Kannan
Balakrishnan
B
Larsson
Mårten
M
Burtnick
Leslie D
LD
Robinson
Robert C
RC
D000199:Actins / Q000737:chemistry*; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry; D018360:Crystallography, X-Ray / Q000379:methods; D018260:Gelsolin / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008856:Microscopy, Fluorescence / Q000379:methods; D008968:Molecular Conformation; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry
D000199:Actins; D018260:Gelsolin; D007477:Ions; D011994:Recombinant Proteins; C065395:scinderin; D002118:Calcium