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Crystal structure of the monoclinic form of Thermotoga maritima Acetyl Esterase TM0077 (apo structure) at 1.76 Angstrom resolution
Structural highlights
FunctionCAH_THEMA Esterase that removes acetyl groups from a number of O-acetylated small substrates, such as acetylated xylose, short xylo-oligosaccharides and cephalosporin C. Has no activity towards polymeric acetylated xylan, 4-methylumbelliferyl acetate or alpha-naphthyl acetate. Able to catalyze rapid hydrolysis of a range of substrates preferably with acetate groups, independent of the alcohol moiety. Exhibits a narrow selectivity for short chain acyl esters (C2-C3). Displays broad substrate specificity by hydrolyzing acetate at 2, 3, and 4 positions of 4-nitrophenyl-beta-D-xylopyranoside (pNP-Xyl) with similar efficiency. Cannot cleave amide linkages.[1] [2] [3] Publication Abstract from PubMedThe carbohydrate esterase family 7 (CE7) belonging to the alpha/beta hydrolase superfamily contains a structurally conserved loop extension element relative to the canonical alpha/beta hydrolase fold. This element called the beta-interface loop contributes 20-30% of the total buried surface area at intersubunit interfaces of the functional hexameric state. To test whether this loop is an enabling region for the structure and function of the oligomeric assembly, we designed a truncation variant of the thermostable CE7 acetyl esterase from Thermotoga maritima (TmAcE). Although deletion of 26 out of 40 residues in the loop had little impact on the hexamer formation, the variant exhibited altered dynamics of the oligomeric assembly and a loss of thermal stability. Furthermore, the mutant lacked catalytic activity. Crystal structures of the variant and a new crystal form of the wild type protein determined at 2.75A and 1.76A, respectively, provide a rationale for the properties of the variant. The hexameric assembly in the variant is identical to that of the wild type and differed only in the lack of buried surface area interactions at the original intersubunit interfaces. This is accompanied by disorder in an extended region of the truncated loop that consequently induces disorder in the neighboring oxyanion hole loop. Overall, the results suggest that the beta-interface loop in CE7 enzymes is dispensable for the oligomeric assembly. Rather, the loop extension event was evolutionarily selected to regulate activity, conformational flexibility and thermal stability. An extended loop in CE7 carbohydrate esterase family is dispensable for oligomerization but required for activity and thermostability.,Singh MK, Manoj N J Struct Biol. 2016 Jun;194(3):434-45. doi: 10.1016/j.jsb.2016.04.008. Epub 2016 , Apr 13. PMID:27085421[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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