Molecular cloning and expression of the cDNA coding for a new member of the S100 protein family from porcine cardiac muscle

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Abstract
We isolated a new calcium-binding protein from porcine cardiac muscle by calcium-dependent hydrophobic and dye-affinity chromatography. It showed an apparent molecular weight of 11 000 on SDS-PAGE. Amino acid sequence determination revealed that the protein contained two calcium-binding domains of the EF-hand motif. The cDNA gene coding for this protein was cloned from the porcine lung cDNA library. Sequence analysis of the cloned cDNA showed that the protein was composed of 99 amino acid residues and its molecular weight was estimated to be 11 179. Immunological and functional characterization showed that the recombinant S100C protein expressed in Escherichia coli was identical to the natural protein. Homologies to calpactin light chain, S100α and β protein were 41.1%, 40.9% and 37.5%, respectively. The protein was expressed at high levels in lung and kidney, and low levels in liver and brain. The tissue distribution was apparently different from those of the other S100 protein family. These results indicate that this protein represents a new member of the S100 protein family, and thus we refer to it as S100C protein