Identification of the missing trans-acting enoyl reductase required for phthiocerol dimycocerosates and phenolglycolipids biosynthesis in M. tuberculosis

Département Mécanismes Moléculaires des Infections Mycobactériennes, Institut de Pharmacologie et de Biologie Structurale, UMR 5089 du CNRS et de l'Université Paul Sabatier, Toulouse, France

^* To whom correspondence should be addressed. Email: christian.chalut{at}ipbs.fr.

	Abstract

Phthiocerol dimycocerosates (DIM) and phenolglycolipids (PGL) are functionally important surface-exposed lipids of Mycobacterium tuberculosis. Their biosynthesis involved the products of several genes clustered in a 70-kb region of the M. tuberculosis chromosome. Among these is PpsD, one of the modular type-I polyketide synthases responsible for the synthesis of the lipid core common to DIM and PGL. Bioinformatic analyses have suggested that this protein lacks a functional enoyl reductase activity domain required for the synthesis of these lipids. We have identified a gene, rv2953, that putatively encodes an enoyl reductase. Mutation in rv2953 prevents conventional DIM formation and leads to the accumulation of a novel DIM-like product. This product is unsaturated between carbons C4 and C5 of phthiocerol. Consistently, complementation of the mutant with a functional pks15/1 gene from M. bovis BCG, resulted in the accumulation of an unsaturated PGL-like substance. When an intact rv2953 gene was re-introduced in the mutant strain, the phenotype reverted to wild-type. These findings indicate that rv2953 encodes a trans-acting enoyl reductase that acts with PpsD in phthiocerol and phenolphthiocerol biosynthesis.