STRUCTURAL CHARACTERIZATION OF EXTRACELLULAR RIBONUCLEASE OF BACILLUS-POLYMYXA - AMINO-ACID-SEQUENCE DETERMINATION AND SPATIAL STRUCTURE PREDICTION

The primary structure of extracellular Bacillus polymyxa ribonuclease (RNase Bpo) was established by mass spectroscopy analysis and automati c Edman degradation of the individual peptides obtained from protein d igestion with Glu-specific protease V8. RNase Bpo consists of 111 amin o acid residues, with a relative molecular weight of 12 607, RNase Bpo is a close structural homolog of RNases of B, amyloliquefaciens (RNas e Pa) and B, intermedius (RNase Bi), the similarity of their primary s tructures being 68%. Molecular modelling of the structure of the compl ex of RNase Bpo with substrate analog d(CGAC) was performed and a spat ial model based on the known crystal structure of RNase Ba complex wit h the corresponding nucleotide was constructed using the methods of in teractive computer graphics and energy minimization. The differences i n the primary and tertiary structures of the enzymes were analyzed in order to understand the substrate specificity of Bacillus RNases.