title: Structure of the S100A4/myosin-IIA complex.
abstract: BACKGROUND
  S100A4, a member of the S100 family of Ca2+-binding proteins, modulates the motility of both non-transformed and cancer cells by regulating the localization and stability of cellular protrusions. Biochemical studies have demonstrated that S100A4 binds to the C-terminal end of the myosin-IIA heavy chain coiled-coil and disassembles myosin-IIA filaments; however, the mechanism by which S100A4 mediates myosin-IIA depolymerization is not well understood.
  
  
  RESULTS
  We determined the X-ray crystal structure of the S100A4Δ8C/MIIA(1908-1923) peptide complex, which showed an asymmetric binding mode for the myosin-IIA peptide across the S100A4 dimer interface. This asymmetric binding mode was confirmed in NMR studies using a spin-labeled myosin-IIA peptide. In addition, our NMR data indicate that S100A4Δ8C binds the MIIA(1908-1923) peptide in an orientation very similar to that observed for wild-type S100A4. Studies of complex formation using a longer, dimeric myosin-IIA construct demonstrated that S100A4 binding dissociates the two myosin-IIA polypeptide chains to form a complex composed of one S100A4 dimer and a single myosin-IIA polypeptide chain. This interaction is mediated, in part, by the instability of the region of the myosin-IIA coiled-coil encompassing the S100A4 binding site.
  
  
  CONCLUSIONS
  The structure of the S100A4/MIIA(1908-1923) peptide complex has revealed the overall architecture of this assembly and the detailed atomic interactions that mediate S100A4 binding to the myosin-IIA heavy chain. These structural studies support the idea that residues 1908-1923 of the myosin-IIA chain heavy represent a core sequence for the S100A4/myosin-IIA complex. In addition, biophysical studies suggest that structural fluctuations within the myosin-IIA coiled-coil may facilitate S100A4 docking onto a single myosin-IIA polypeptide chain.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA. anne.bresnick@einstein.yu.edu.
authors.forename: Udupi A
authors.initials: UA
authors.lastname: Ramagopal
authors.forename: Natalya G
authors.initials: NG
authors.lastname: Dulyaninova
authors.forename: Kristen M
authors.initials: KM
authors.lastname: Varney
authors.forename: Paul T
authors.initials: PT
authors.lastname: Wilder
authors.forename: Sridevi
authors.initials: S
authors.lastname: Nallamsetty
authors.forename: Michael
authors.initials: M
authors.lastname: Brenowitz
authors.forename: David J
authors.initials: DJ
authors.lastname: Weber
authors.forename: Steven C
authors.initials: SC
authors.lastname: Almo
authors.forename: Anne R
authors.initials: AR
authors.lastname: Bresnick
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009154:Mutation; D009218:Myosins / Q000378:metabolism; D024507:Nonmuscle Myosin Type IIA / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins; C077591:S100A4 protein, human; D024507:Nonmuscle Myosin Type IIA; D009218:Myosins