Oligomerization and divalent ion binding properties of the S100P protein: a Ca2+/Mg2+-switch model.
S100P is a 95 amino acid residue protein which belongs to the S100 family of proteins containing two putative EF-hand Ca2+-binding motifs. In order to characterize conformational properties of S100P in the presence and absence of divalent cations (Ca2+, Mg2+ and Zn2+) in solution, we have analyzed hydrodynamic and spectroscopic characteristics of wild-type and several variants (Y18F, Y88F and C85S) of S100P using equilibrium centrifugation, gel-filtration chromatography, circular dichroism and fluorescence spectroscopies. Analysis of the experimental data shows the following. (1) In agreement with the predictions there are two Ca2+-binding sites in the S100P molecule with different affinity; the high affinity binding site has an apparent binding constant of approximately 10(7) M-1 and the low affinity binding site has an apparent binding constant of approximately 10(4) M-1. (2) The high and low affinity Ca2+-binding sites are located in the C and N-terminal parts of the S100P molecule, respectively. (3) These C and N-terminal sites can also bind other divalent ions. The C-terminal site binds Zn2+ (with relatively low affinity approximately 10(3) M-1), but not Mg2+. The N-terminal site binds Mg2+ with the apparent binding constant approximately 10(2) M-1. (4) Binding of Ca2+ to the C-terminal site and binding of Mg2+ to the N-terminal site occur in the physiological concentration range of these ions (micromolar for Ca2+ and millimolar for Mg2+). (5) Oligomerization state of the S100P molecule appears to change upon addition of Ca2+. On the basis of these observations a plausible model for S100P as a Ca2+/Mg2+ switch has been proposed.
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA.
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Gribenko
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Makhatadze
D000595:Amino Acid Sequence; D064026:Calbindins; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002850:Chromatography, Gel; D002942:Circular Dichroism; D008274:Magnesium / Q000378:metabolism*; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D009363:Neoplasm Proteins; D011487:Protein Conformation; D064030:S100 Calcium Binding Protein G / Q000737:chemistry; D009418:S100 Proteins; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D014443:Tyrosine / Q000378:metabolism; D014461:Ultracentrifugation; D015032:Zinc / Q000378:metabolism
D064026:Calbindins; D002135:Calcium-Binding Proteins; D009363:Neoplasm Proteins; D064030:S100 Calcium Binding Protein G; D009418:S100 Proteins; C103003:S100P protein, human; D014443:Tyrosine; D008274:Magnesium; D015032:Zinc; D002118:Calcium