|
type |
Journal Article |
authors |
Cheng, Y.Q.
Walton, J.D.
|
title |
A eukaryotic alanine racemase gene involved in cyclic peptide biosynthesis |
journal |
J Biol Chem. |
Activity |
5.1.1.1 |
Family |
5.1.1.1.b |
sel |
selected |
ui |
10671527 |
year |
(2000) |
volume |
275 |
number |
7 |
pages |
4906-4911 |
| |
abstract |
The cyclic tetrapeptide HC-toxin is an essential virulence determinant for the plant pathogenic fungus Cochliobolus carbonum and an inhibitor of histone deacetylase. The major form of HC-toxin contains the D-isomers of Ala and Pro. The non-ribosomal peptide synthetase that synthesizes HC-toxin has only one epimerizing domain for conversion of L-Pro to D-Pro; the source of D-Ala has remained unknown. Here we present the cloning and characterization of a new gene involved in HC-toxin biosynthesis, TOXG. TOXG is present only in HC-toxin-producing (Tox2(+)) isolates of C. carbonum. TOXG is able to support D-Ala-independent growth of a strain of Escherichia coli defective in D-Ala synthesis. A C. carbonum strain with both of its copies of TOXG mutated grows normally in culture, and although it no longer makes the three forms of HC-toxin that contain D-Ala, it still makes a minor form of HC-toxin that contains Gly in place of D-Ala. The addition of D-Ala to the culture medium restores production of the D-Ala-containing forms of HC-toxin by the toxG mutant. The toxG mutant has only partially reduced virulence. It is concluded that TOXG encodes an alanine racemase whose function is to synthesize D-Ala for incorporation into HC-toxin.
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last changed |
2009/07/02 13:32 |
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