NMR-derived three-dimensional solution structure of protein S complexed with calcium

Structure. 1994 Feb 15;2(2):107-22. doi: 10.1016/s0969-2126(00)00013-7.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Calcium / metabolism*
  • Computer Graphics
  • Crystallins / chemistry*
  • Magnetic Resonance Spectroscopy / methods
  • Models, Molecular
  • Molecular Sequence Data
  • Myxococcus xanthus / metabolism
  • Protein Conformation*
  • Protein Folding*
  • Protein S / chemistry*
  • Protein S / metabolism*
  • Protein Structure, Secondary*
  • Solutions


  • Crystallins
  • Protein S
  • Solutions
  • Calcium