Determination of the structure of the novel polypeptide containing aspartic acid and arginine which is found in Cyanobacteria.

The polypeptide contained in the cyanophycin granule, a characteristic cyanobacterial subcellular inclusion, is shown to be a highly branched structure consisting of a polyaspartic acid core to which arginyl residues are attached at each free carboxyl group of the polyaspartic acid. The evidence supporting such a model includes: (i) The resistance of the polypeptide to a variety of enzymatic procedures commonly used to degrade linear polypeptide chains. (ii) The inability to degrade the polypeptide from the amino terminal using sequential Edman degradation. (iii) The preferential relase of arginine following hydrolysis of the polypeptide in dilute acid (0.03 M acetic acid, 105 degrees C). (iv) The demonstration by chemical linkage analysis that both the carboxyl groups of aspartic acid are unavailable for reduction and must therefore by involved in covalent linkages and that many arginyl residues can be reduced and therefore must not be involved in covalent linkage. (v) The removal of approximately 75% of the arginine from the polypeptide by chemical treatment of the polypeptide using methods designed to cleave carboxyl-terminal amino acids. The highly branched structure of the cyanophycin granule polypeptide is similar in form to synthetically produced multichain polyamino acids, and using the nomenclature for describing multichain polyamino acids, it is proposed that the cyanophycin granule polypeptide be called multi-L-arginyl- -polyaspartic acid.