Chorismate mutase of<Emphasis Type="Italic"> Thermus thermophilus</Emphasis> is a monofunctional AroH class enzyme inhibited by tyrosine |
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Authors: | Kerstin?Helmstaedt Gabriele?Heinrich Rainer?Merkl Email author" target="_blank">Gerhard?H?BrausEmail author |
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Institution: | (1) Abteilung Molekulare Mikrobiologie und Genetik, Institut für Mikrobiologie und Genetik, Grisebachstrasse 8, 37077 Göttingen, Germany;(2) Abteilung Molekulare Genetik und Präparative Molekularbiologie, Georg-August-Universität, Grisebachstrasse 8, Institut für Mikrobiologie und Genetik, 37077 Göttingen, Germany |
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Abstract: | aroG, encoding the monofunctional chorismate mutase (TtCM) of the thermophilic gram-negative bacterium Thermus thermophilus, was cloned and its gene product characterized. TtCM was purified to homogeneity on an SDS polyacrylamide gel as a His-fusion protein with a deduced molecular mass of 15.8 kDa. The enzyme belongs to the rare group of AroH-type chorismate mutases which are mainly found in gram-positive bacteria of the Bacillus/Clostridia group and have recently also been described for gram-negative organisms. The native molecular mass is consistent with a pseudo- / barrel enzyme that is organized as a trimer. Comparison of the enzyme s structure with that of its mesophilic counterpart from Bacillus revealed an increase in hydrophilicity on the protein s surface, greater hydrophobicity in cavities within the protein, and greater restriction of conformational freedom, features that contribute to the thermal stability of this chorismate mutase. The kinetic data show Michaelis-Menten substrate saturation with a K
m of 290 M, and a k
cat/K
m value of 180 s–1 mM–1. TtCM was inhibited by tyrosine with a K
i
=34 M, possibly in a competitive manner. |
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Keywords: | Chorismate mutase aroG TtCM BsCM AroH AroQ |
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