although MCP hydrolases have a catalytic serine in the active site, the mechanism proceeds via a geminal diol, rather than an acyl-enzyme intermediate, reaction mechanism of the hydrolysis reaction, overview. MCP hydrolases accept alternative nucleophiles in addition to water, and accepts hydroxylamine in the C-C cleavage reaction. MhpC has a typical serine-hydrolase catalytic triad (Ser107, Asp228 and His256), but mechanistic studies indicate that the serine in the active site does not act as a nucleophile in the hydrolysis, but rather the reaction proceeds via general base catalysis.The serine in the active site might stabilise the oxyanion intermediate by hydrogen bonding
the enzyme is able to catalyse carbon-carbon bond formation. In addition to its natural substrate 2-hydroxy-6-oxonona-1,9-dienedioic acid, enzyme MhpC also hydrolyses various analogues and also the hydrolysis of ester bonds of monoethyl adipate and 4-nitrophenyl valerate. The H114A mutant of the enzyme also hydrolyses 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid, HOPDA, a substrate of enzyme BphD, EC 18.104.22.168. Incubation of monomethyl succinate and ethyl 2-hydroxypentadienoate with the wild-type freeze-dried MhpC in hexane result in C-C bond formation product
hanging-drop vapour-diffusion method. The 2.1 A resolution X-ray structure of the native enzyme determined from orthorhombic crystals confirms that it is a member of the alpha/beta hydrolase fold family, comprising eight beta-strands interconnected by loops and helices. The 2.8 A resolution structure of the enzyme cocrystallized with the non-hydrolysable substrate analogue 2,6-diketo-nona-1,9-dioic acid confirms the location of the active site in a buried channel including Ser110, His263 and Asp235, postulated contributors to a serine protease-like catalytic triad in homologous enzymes
shows twofold-reduced catalytic efficiency, ruling out a catalytic role, but shows a fivefold-reduced KM for the natural substrate, and an ability to process an aryl-containing substrate, implying a role for His114 in positioning of the substrate
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3-(3-hydroxyphenyl)propionic acid, 3-(2-hydroxyphenyl)propionic acid, 3-(2,3-dihydroxyphenyl)propionic acid or hydrocinnamic acid or cis-3-(3-carboxyethyl)-3,5-cyclohexadiene-1,2-diol are poor inducers