Characterization of human brain S100 protein fraction: amino acid sequence of S100 beta

Two major components of human brain S100 fraction were purified by HPLC and an amino acid sequence was elucidated for the S100 beta component. Human S100 proteins showed absorption spectra and amino acid compositions similar to S100 alpha and S100 beta from bovine brain. However, the relative amounts of the human proteins were 4% S100 alpha and 96% S100 beta by weight, while the bovine protein distribution was 47% S100 alpha and 53% S100 beta by weight. An amino acid sequence of human S100 beta was established by analysis of overlapping fragments generated by cyanogen bromide and trypsin cleavage. Three amino acid sequence differences between the human and bovine S100 beta were found at residues 7, 62, and 80. These differences were chemically conservative and compatible with minimum single base changes in the codon structures. These results document that S100 beta is a conserved protein among mammals and provide the necessary foundation for current clinical studies.