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ThrH, a homoserine kinase isozyme with in vivo phosphoserine phosphatase activity in Pseudomonas aeruginosa

Christian Clepet^1,

Françoise Borne^1,

LCB, Centre National de la Recherche Scientifique, 31 chemin J Aiguier, BP71, 13277 Marseille, France
LISM, Centre National de la Recherche Scientifique, 31 chemin J Aiguier, BP71, 13277 Marseille, France

Author for correspondence: Jean-Claude Patte. Tel: +33 4 91 16 41 99. Fax: +33 4 91 71 89 14. e-mail: patte@ibsm.cnrs-mrs.fr

ABSTRACT

Summary: Homoserine kinase, the product of the thrB gene, catalyses an obligatory step of threonine biosynthesis. In Pseudomonas aeruginosa, unlike Escherichia coli, inactivation of the previously identified thrB gene does not result in threonine auxotrophy. A new gene, named thrH, was isolated that, when expressed in E. coli thrB mutant strains, results in complementation of the mutant phenotype. In P. aeruginosa, threonine auxotrophy is observed only when both thrB and thrH are simultaneously inactivated. Thus, thrH encodes a protein with an in vivo homoserine-kinase-like activity. Surprisingly, thrH overexpression allows complementation of serine auxotrophy of E. coli and P. aeruginosa serB mutants. These mutants are affected in the phosphoserine phosphatase protein, an enzyme involved in serine biosynthesis. Comparison analysis revealed sequence homology between ThrH and the SerB proteins from different organisms. This could explain the in vivo phosphoserine phosphatase activity of ThrH when overproduced. ThrH differs from the protein encoded by the serB gene which was identified in P. aeruginosa. Thus, two SerB-like proteins co-exist in P. aeruginosa, a situation also found in Mycobacterium tuberculosis.

Present address: Institut de Biochimie et Génétique Cellulaire, CNRS, 33077 Bordeaux, France.

Present address: Genomics/Rhóne-Poulenc, 91006 Evry Cedex, France.

This article has been cited by other articles:

				S. K. Singh, K. Yang, S. Karthikeyan, T. Huynh, X. Zhang, M. A. Phillips, and H. Zhang The thrH Gene Product of Pseudomonas aeruginosa Is a Dual Activity Enzyme with a Novel Phosphoserine:Homoserine Phosphotransferase Activity J. Biol. Chem., March 26, 2004; 279(13): 13166 - 13173. [Abstract] [Full Text] [PDF]