title: Human S100b protein: formation of a tetramer from synthetic calcium-binding site peptides.
abstract: Human brain S100b protein is a unique calcium-binding protein comprised of two identical 91-amino acid polypeptide chains that each contain two proposed helix-loop-helix (EF-hand) calcium-binding sites. In order to probe the assembly of the four calcium-binding sites in S100b, a peptide comprised of the N-terminal 46 residues of S100b protein was synthesized and studied by CD and 1H NMR spectroscopies as a function of concentration and temperature. At relatively high peptide concentrations and in the absence of calcium, the peptide exhibited a significant proportion of alpha-helix (45%). Decreasing the peptide concentration led to a loss of alpha-helix as monitored by CD spectroscopy and coincident changes in the 1H NMR spectrum. These changes were also observed by 1H NMR spectroscopy as a function of temperature where it was observed that the Tm of the peptide was lowered approximately 14 degrees C with a 17-fold decrease in peptide concentration. Sedimentation equilibrium studies were used to determine that the peptide formed a tetramer in solution in the absence of calcium. It is proposed that this tetrameric fold also occurs in S100b and is a result of the interaction of portions of all four calcium-binding sites.
authors.affiliation: Department of Biochemistry and McLaughlin Macromolecular Structure Facility, University of Western Ontario, London, Canada.
authors.forename: C
authors.initials: C
authors.lastname: Donaldson
authors.forename: K R
authors.initials: KR
authors.lastname: Barber
authors.forename: C M
authors.initials: CM
authors.lastname: Kay
authors.forename: G S
authors.initials: GS
authors.lastname: Shaw
mesh_terms: D000595:Amino Acid Sequence; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D002942:Circular Dichroism; D018257:Helix-Loop-Helix Motifs; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009414:Nerve Growth Factors; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins / Q000737:chemistry*; D013696:Temperature; D014461:Ultracentrifugation
chemical_list: D002135:Calcium-Binding Proteins; D009414:Nerve Growth Factors; D010455:Peptides; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins; C579160:S100B protein, human; D002118:Calcium