Single-strand-specific nuclease from Basidiobolus haptosporus (Nuclease Bh1)

Abstract

Nuclease Bh1 is a multifunctional enzyme and catalyses the hydrolysis of ssDNA, 3’AMP and RNA in a ratio of approximately 1:1:0.05. It is a single polypeptide chain of 30 kDa and contains 15% carbohydrate. All three activities of the enzyme showed the same pI, indicating that they are associated with the same protein. The ssDNase, 3’AMPase and RNase activities of nuclease Bh1 showed the same pH and temperature optima and stability. Nuclease Bh1 neither showed an obligate requirement metal ion for its activity nor the activity was stimulated in presence of metal ions but it is a zinc metallo-protein. Moreover, they exhibited similar sensitivity towards divalent cations, metal chelators, thiol reagents, protein denaturants and guanosine 5’ nucleotides. It hydrolyzed DNA endonucleolytically with a preference for guanylic acid linkages whereas; it showed an endo-exo mode of action on RNA, with a preference for adenylic acid linkages. Cytidylic acid linkages were resistant to cleavage. The phosphor-monoesterase activity of the enzyme is 3’ ribonucleotide specific. Active site nature suggested the involvement of lysine in substrate binding and carboxylate in catalysis. Key words: Basidiobolus haptosporus, single-strand-specific nuclease, nuclease Bh1, multifunctional enzyme, characteristics.