Amino acid sequence of the intracellular cysteine proteinase inhibitor cystatin B from human liver

The complete amino acid sequence of the cysteine proteinase inhibitor cystatin B (formerly named CPI-B) from human liver was determined. The 98-residue sequence (M r = 11,175) was obtained by automated solid-phase Edman degradation of a large cyanogen bromide fragment and peptides generated by enzymatic cleavage. The protein starts with a blocked Met-Met sequence which is presumably N-acetylated. The sequence shows that human cystatin B is a member of the family of intracellular cystatins; it is 79% identical with cystatin β from rat liver, but contains only a single cysteine. Human cystatin B is able to form a dimer stabilized by noncovalent forces.