Structural and biochemical characterization of inhibitor-1α

Inhibitor-.1 alpha is one of the isoforms of human protein phosphatase inhibitor-1. It is a product of alternative splicing of inhibitor-] gene and lacks 51 internal amino acids from residue 84 to 134 of inhibitor-L Here we have characterized the structural and biochemical properties of inhibitor-ii. Structural analysis of recombinant inhibitor-Ii by NMR spectroscopy revealed that inhibitor-ii adopts apredominantly random coil conformation. Excluding the region from residue 84 to 134 of inhibitor.1, the structural features of inhibitor-] and inhibitor-1 alpha are almost the same as each other. The IC50 value of inhibitor-1 alpha in inhibition of Protein phosphatase-1 (PPI) is comparable to that of inhibitor-1, indicating that inhibitor-1 alpha is a potent inhibitor of PPI when Thr-35 is phosphorylated by PKA. For phosphorylation by PKA and dephosphorylation by protein phosphatase-1, -2A, and -2B, the measured kinetic parameters of inhibitor-1 alpha very close to those of inhibitor-L Taken together, these results suggest that inhibitor-1 alpha preserves the structure of inhibitor- L the PPI inhibitory activity and the functional specificities toward phosphorylation by PKA and dephosphorylation by proteinphosphatase-1, -2A, and -2B.