Different Active-Site Loop Orientation in Serine Hydrolases versus Acyltransferases

  1. Get@NRC: Different Active-Site Loop Orientation in Serine Hydrolases versus Acyltransferases (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1002/cbic.201000693
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Journal titleChemBioChem
Pages768776; # of pages: 9
Subjectacyltransferase; esterase; serine dehydratase; triacylglycerol lipase; amino acid sequence; article; comparative study; crystal structure; enzyme active site; enzyme structure; Haemophilus influenzae; hydrolysis; nonhuman; orientation; priority journal; Pseudomonas fluorescens; reaction analysis; X ray crystallography; Acyltransferases; Catalytic Domain; Crystallography, X-Ray; Esterases; Haemophilus influenzae; Hydrolases; Models, Molecular; Protein Conformation; Pseudomonas fluorescens; Pseudomonas fluorescens
AbstractAcyl transfer is a key reaction in biosynthesis, including synthesis of antibiotics and polyesters. Although researchers have long recognized the similar protein fold and catalytic machinery in acyltransferases and hydrolases, the molecular basis for the different reactivity has been a long-standing mystery. By comparison of X-ray structures, we identified a different oxyanion-loop orientation in the active site. In esterases/lipases a carbonyl oxygen points toward the active site, whereas in acyltransferases a NH of the main-chain amide points toward the active site. Amino acid sequence comparisons alone cannot identify such a difference in the main-chain orientation. To identify how this difference might change the reaction mechanism, we solved the X-ray crystal structure of Pseudomonas fluorescens esterase containing a sulfonate transition-state analogue bound to the active-site serine. This structure mimics the transition state for the attack of water on the acyl-enzyme and shows a bridging water molecule between the carbonyl oxygen mentioned above and the sulfonyl oxygen that mimics the attacking water. A possible mechanistic role for this bridging water molecule is to position and activate the attacking water molecule in hydrolases, but to deactivate the attacking water molecule in acyl transferases. All in the loop: A structure comparison of hydrolases and acyl transferases revealed a different conformation of the main chain in the oxyanion loop. Hydrolases point a C=O, whereas acytransferase point a NH, toward the active site. An X-ray structure of a hydrolase containing a sulfonate transition-state analogue show how this loop interacts with the attacking water. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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AffiliationNational Research Council Canada (NRC-CNRC); NRC Biotechnology Research Institute (BRI-IRB)
Peer reviewedYes
NPARC number21271407
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Record identifier62ed4eae-0863-42da-a6ed-dfd23f886e25
Record created2014-03-24
Record modified2016-05-09
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