Primary structure and binding properties of calgranulin C, a novel S100-like calcium-binding protein from pig granulocytes.
In this paper we report the biochemical characterization of calgranulin C, a new member of the S100 protein family. The protein is highly abundant in the cytosol of pig granulocytes, with relatively small amounts in lymphocytes. A simple protocol for the rapid purification of calgranulin C is described. The purified protein migrates as a single entity on SDS-polyacrylamide gel electrophoresis while it has two isoforms focusing at pH 5.8 and 5.5. Gel filtration and cross-linking experiments indicate that calgranulin C is capable of dimerization. The complete amino acid sequence was determined by Edman degradation of peptides generated by trypsin and V8 protease digestion. Calgranulin C consists of 91 residues and has a calculated molecular mass of 10,614 daltons. This value is virtually identical to that obtained by electrospray mass spectrometry. Sequence analysis predicts two EF-hand calcium-binding motifs, the first having an extended loop that is distinctive of the S100 protein family. The metal-binding properties were studied by means of a direct 45Ca(2+)-binding assay and by tyrosine fluorescence titration. Calgranulin C binds not only calcium but also zinc ions. A single high affinity Zn(2+)-binding site per monomer was evidenced by fluorimetric titration. Zinc binding to calgranulin C induces a remarkable increase in the protein affinity for calcium; in the absence of zinc, the protein binds 1 Ca2+/monomer with a binding constant of about 2 x 10(4) M-1, whereas the Zn(2+)-loaded form binds 2 Ca2+/monomer with Ka values of approximately 3 x 10(7) and 6 x 10(4) M-1. Circular dichroism analysis showed that the binding of calcium to calgranulin C induces a 15% decrease in the apparent alpha-helix content. This result and the calcium-dependent binding of the protein to a phenyl-Superose column strongly suggest that calgranulin C undergoes a gross conformational change upon calcium binding, thus supporting the idea that this protein may be involved in Ca(2+)-dependent signal transduction events.
Instituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina.
E C
EC
Dell'Angelica
C H
CH
Schleicher
J A
JA
Santomé
D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006098:Granulocytes / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011487:Protein Conformation; D009418:S100 Proteins / Q000737:chemistry / Q000378:metabolism; D000067616:S100A12 Protein; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013552:Swine; D014443:Tyrosine / Q000737:chemistry
D002135:Calcium-Binding Proteins; D009418:S100 Proteins; D000067616:S100A12 Protein; C090441:S100A12 protein, human; D014443:Tyrosine