title: NMR-derived three-dimensional solution structure of protein S complexed with calcium.
abstract: BACKGROUND
  Protein S is a developmentally-regulated Ca(2+)-binding protein of the soil bacterium Myxococcus xanthus. It functions by forming protective, multilayer spore surface assemblies which may additionally act as a cell-cell adhesive. Protein S is evolutionarily related to vertebrate lens beta gamma-crystallins.
  
  
  RESULTS
  The three-dimensional solution structure of Ca(2+)-loaded protein S has been determined using multi-dimensional heteronuclear NMR spectroscopy. (Sixty structures were calculated, from which thirty were selected with a root mean square difference from the mean of 0.38 A for backbone atoms and 1.22 A for all non-hydrogen atoms.) The structure was analyzed and compared in detail with X-ray crystallographic structures of beta gamma-crystallins. The two internally homologous domains of protein S were compared, and hydrophobic cores, domain interfaces, surface ion pairing, amino-aromatic interactions and potential modes of multimerization are discussed.
  
  
  CONCLUSIONS
  Structural features of protein S described here help to explain its overall thermostability, as well as the higher stability and Ca2+ affinity of the amino-terminal domain relative to the carboxy-terminal domain. Two potential modes of multimerization are proposed involving cross-linking of protein S molecules through surface Ca(2+)-binding sites and formation of the intramolecular protein S or gamma B-crystallin interdomain interface in an intermolecular content. This structural analysis may also have implications for Ca(2+)-dependent cell-cell interactions mediated by the vertebrate cadherins and Dictyostelium discoideum protein gp24.
authors.affiliation: Division of Molecular and Structural Biology, Ontario Cancer Institute, Toronto, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Bagby
authors.forename: T S
authors.initials: TS
authors.lastname: Harvey
authors.forename: S G
authors.initials: SG
authors.lastname: Eagle
authors.forename: S
authors.initials: S
authors.lastname: Inouye
authors.forename: M
authors.initials: M
authors.lastname: Ikura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D003196:Computer Graphics; D003459:Crystallins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016941:Myxococcus xanthus / Q000378:metabolism; D011487:Protein Conformation; D017510:Protein Folding; D017293:Protein S / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D012996:Solutions
chemical_list: D003459:Crystallins; D017293:Protein S; D012996:Solutions; D002118:Calcium