Comparison of mesophilic and thermophilic feruloyl esterases: characterization of their substrate specificity for methyl phenylalkanoates.
The active sites of feruloyl esterases from mesophilic and thermophilic sources were probed using methyl esters of phenylalkanoic acids. Only 13 out of 26 substrates tested were significant substrates for all the enzymes. Lengthening or shortening the aliphatic side chain while maintaining the same aromatic substitutions completely abolished activity for both enzymes, which demonstrates the importance of the correct distance between the aromatic group and the ester bond. Maintaining the phenylpropanoate structure but altering the substitutions of the aromatic ring demonstrated that the type-A esterase from the mesophilic fungus Fusarium oxysporum (FoFaeA) showed a preference for methoxylated substrates, in contrast to the type-B esterase from the same source (FoFaeB) and the thermophilic type-B (StFaeB) and type-C (StFaeC) from Sporotrichum thermophile, which preferred hydroxylated substrates. All four esterases hydrolyzed short chain aliphatic acid (C2-C4) esters of p-nitrophenol, but not the C12 ester of laurate. All the feruloyl esterases were able to release ferulic acid from the plant cell wall material in conjunction with a xylanase, but only the type-A esterase FoFaeA was effective in releasing the 5,5' form of diferulic acid. The thermophilic type-B esterase had a lower catalytic efficiency than its mesophilic counterpart, but released more ferulic acid from plant cell walls.
Topakas
Evangelos
E
Biotechnology Laboratory, Chemical Engineering Department, National Technical University of Athens, 5 Iroon Polytechniou Str, Zografou Campus, 15700 Athens, Greece.
Christakopoulos
Paul
P
Faulds
Craig B
CB
D001665:Binding Sites; D002264:Carboxylic Acids / Q000737:chemistry; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005670:Fusarium / Q000201:enzymology; D007700:Kinetics; D015335:Molecular Probes / Q000737:chemistry; D015394:Molecular Structure; D013175:Sporothrix / Q000201:enzymology; D013379:Substrate Specificity; D013696:Temperature
D002264:Carboxylic Acids; D015335:Molecular Probes; D002265:Carboxylic Ester Hydrolases