A novel engineered subtilisn BPN' lacking a low barrier hydrogenbond in the catalytic triad
The low-barrier hydrogen bond (LBHB) between the Asp and Hisresidues of the catalytic triad in a serine protease was perturbed via the D32C mutation in subtilisin BPN' (Bacillus protease N'). This mutant enzyme catalyzes the hydrolysis of N-Suc-Ala-Ala-Pro-Phe-SBzl with ak(cat)/K(m) value that is only 8-fold reduced from that of the wild-type(WT) enzyme. The value of k(cat)/K(m) for the corresponding p-nitroanilide (pNA) substrate is only 50-fold lower than that of the WT enzyme (DeltaDeltaG++ =2.2 kcal/mol). The pK(a) controlling the ascending limb of the pH versus k(cat)/K(m) profile is lowered from 7.01 (WT) to6.53 (D32C),implying that any hydrogen bond replacing that between Asp32 and His64 of the WT enzyme most likely involves the neutral thiol rather than the thiolate form of Cys32. It is shown by viscosity variation that the reaction of WT subtilisin with N-Suc-Ala-Ala-Pro-Phe-SBzl is 50 percent (sucrose) to 100 percent (glycerol) diffusion-controlled, while that of the D32C construct is 29 percent (sucrose) to 76 percent (glycerol) diffusion-controlled. The low-field NMR resonance of 18 ppm that has been assigned to a proton shared by Asp32 and His64, and is considered diagnostic of a LBHB in the WT enzyme, is not present in D32C subtilisin. Thus, the LBHB is not an inherent requirement for substantial rate enhancement for subtilisin.
- Research Organization:
- COLLABORATION - UCBerkeley
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 892205
- Report Number(s):
- LBNL--51094; BnR: 400412000
- Journal Information:
- Biochemistry, Journal Name: Biochemistry Journal Issue: 35 Vol. 40
- Country of Publication:
- United States
- Language:
- English
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