A Solid Phase Synthetic Study of Structure-Function Relationships in the Amino-terminal Region of Staphylococcal Nuclease

Synthetic peptides corresponding to residues (6 through 47), (9 through 47), (10 through 47), (11 through 47), (12 through 47), (16 through 47), and (18 through 47) in staphylococcal nuclease were prepared by the Merrifield solid phase method. Whereas synthetic-(6–47) and synthetic-(9–47) are about equally effective in generating both RNase and DNase activity upon mixing with native nuclease tryptic fragment nuclease-T-(49–149), synthetic-(10–47) is only partially effective and synthetic-(11–47) through synthetic-(18–47) generate essentially no activity. Synthetic-(6–47) is also the most capable of forming a stable complex with nuclease-T-(49–149), as judged by the resistance of the DNase activity of this semisynthetic nuclease-T species to destruction by trypsin in the presence of deoxythymidine 3',5'-diphosphate and Ca++, as well as by the extent of the shift and intensification of the fluorescence emission spectrum of the tryptophanyl residue in nuclease-T-(49–149). By these latter criteria, synthetic-(9–47) and synthetic-(10–47) form progressively weaker nuclease-T complexes than does synthetic-(6–47). On the other hand, all of the synthetic peptides through synthetic-(18–47) are able to bind, at least slightly, with nuclease-T-(49–149) as judged by the ability to enhance the binding of 125I-nuclease-T-(49–149) to antinuclease antibody. The results for these peptides, considered together with structural features in the 2 A model of nuclease elucidated by Dr. F. A. Cotton and his associates, suggest important structural functions for residues lysine 9 and glutamic acid 10 in both nuclease-T and nuclease.