Deletion of the Ω-loop in the active site of staphylococcal nuclease. 1. Effect on catalysis and stability

The high-resolution X-ray structure of wild-type staphylococcal nuclease (E43 SNase) suggests that Glu 43 acts a general basic catalyst to assist the attack of water on a phosphodiester substrate. Glu 43 is located at the base of the solvent-exposed and conformationally mobile Ω-loop in the active site of E43 SNase having the sequence Glu 43 -Thr 44 -Lys 45 -His 46 -Pro 47 -Lys 48 -Gly 50 -Val 51 -Glu 52 , where the γ-carboxylate of Glu 52 is bonded to the amide hydrogen of Glu 43.