Cyanophycinase, a peptidase degrading the cyanobacterial reserve material multi‐L‐arginyl‐poly‐L‐aspartic acid (cyanophycin)

Abstract

The branched polypeptide multi‐ l ‐arginyl‐poly‐ l ‐aspartic acid, also called cyanophycin, is a water‐insoluble reserve material of cyanobacteria. The polymer is degraded by a specific hydrolytic enzyme called cyanophycinase. By heterologous expression in Escherichia coli , a gene encoding cyanophycinase has been identified in the sequenced genome of Synechocystis sp. PCC 6803. The gene, designated cphB , codes for a protein of 29.4 kDa. The high level of expression of active cyanophycinase in E. coli from the Synechocystis gene allowed for its purification to electrophoretic homogeneity. The enzyme, which appears to be specific for cyanophycin, hydrolysed the polymer to a dipeptide consisting of aspartic acid and arginine. Based on inhibitor sensitivity and primary sequence, cyanophycinase appears to be a serine‐type exopeptidase related to dipeptidase E [Conlin, C.A., Haakensson, K., Liljas, A. & Miller, C.G. (1994) J. Bacteriol. 176 , 166–172].