3hi4

Switching catalysis from hydrolysis to perhydrolysis in P. fluorescens esterase

spinqualitylabelsall models 3hi4, resolution 2.25Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 3hi4 is a 6 chain structure with sequence from Pseudomonas fluorescens. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Ligands: ACT, GOL, SO4 Related: 1va4 Resources: FirstGlance, OCA, RCSB, PDBsum Function [ESTE_PSEFL] Bifunctional enzyme, capable of both ester hydrolysis and halogenation. Has a low bromoperoxidase activity. Acts on many phenolic esters. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMed Many serine hydrolases catalyze perhydrolysis, the reversible formation of peracids from carboxylic acids and hydrogen peroxide. Recently, we showed that a single amino acid substitution in the alcohol binding pocket, L29P, in Pseudomonas fluorescens (SIK WI) aryl esterase (PFE) increased the specificity constant of PFE for peracetic acid formation >100-fold [Bernhardt et al. (2005) Angew. Chem., Int. Ed. 44, 2742]. In this paper, we extend this work to address the three following questions. First, what is the molecular basis of the increase in perhydrolysis activity? We previously proposed that the L29P substitution creates a hydrogen bond between the enzyme and hydrogen peroxide in the transition state. Here we report two X-ray structures of L29P PFE that support this proposal. Both structures show a main chain carbonyl oxygen closer to the active site serine as expected. One structure further shows acetate in the active site in an orientation consistent with reaction by an acyl-enzyme mechanism. We also detected an acyl-enzyme intermediate in the hydrolysis of epsilon-caprolactone by mass spectrometry. Second, can we further increase perhydrolysis activity? We discovered that the reverse reaction, hydrolysis of peracetic acid to acetic acid and hydrogen peroxide, occurs at nearly the diffusion limited rate. Since the reverse reaction cannot increase further, neither can the forward reaction. Consistent with this prediction, two variants with additional amino acid substitutions showed 2-fold higher k(cat), but K(m) also increased so the specificity constant, k(cat)/K(m), remained similar. Third, how does the L29P substitution change the esterase activity? Ester hydrolysis decreased for most esters (75-fold for ethyl acetate) but not for methyl esters. In contrast, L29P PFE catalyzed hydrolysis of epsilon-caprolactone five times more efficiently than wild-type PFE. Molecular modeling suggests that moving the carbonyl group closer to the active site blocks access for larger alcohol moieties but binds epsilon-caprolactone more tightly. These results are consistent with the natural function of perhydrolases being either hydrolysis of peroxycarboxylic acids or hydrolysis of lactones. Switching Catalysis from Hydrolysis to Perhydrolysis in Pseudomonas fluorescens Esterase (,).,Yin DL, Bernhardt P, Morley KL, Jiang Y, Cheeseman JD, Purpero V, Schrag JD, Kazlauskas RJ Biochemistry. 2010 Feb 10. PMID:20112920 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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