Carbon and energy metabolism in Chlamydia trachomatis

Abstract

For years, the obligate intracellular eubacteria chlamydiae, were speculated to be energy parasites, completely dependent on the host cell for high-energy intermediates. In order to gain a better understanding of chlamydial biochemistry and intracellular parasitism, carbon and energy metabolism was studied. Four ' C. trachomatis' genes encoding energy-producing enzymes of the glycolytic and pentose phosphate pathways specifically, glyceraldehyde-3-phosphate dehydrogenase (GA3PDH), phosphoglycerate kinase (PGK), pyruvate kinase (PK) and glucose-6-phosphate dehydrogenase or zwichenferment (ZWF) were cloned, sequenced and expressed as recombinant proteins in 'Escherichia coli'. Res lts indicate that the deduced amino acid sequence obtained showed high homology to other respective GA3PDH, PGK, PK, and ZWF enzymes, all four genes were expressed during the chlamydial life cycle and the recombinant proteins were active. The key, regulatory enzyme PK was further analyzed and kinetic studies showed that 'C. trachomatis' PK (CTPK) requires cations for activity, can use alternative NDPs as phosphate acceptors and is allosterically inhibited by ATP, GTP and AMP, a metabolite that normally activates bacterial PKs. Surprisingly, CTPK is also allosterically activated by fructose-2,6-bisphosphate, a metabolite found only in eukaryotes. Studies on glycogen and carbon metabolism in ' C. trachomatis' indicated that chlamydia was capable of limited growth in the presence of certain gluconeogenic substrates but was not able to synthesize glycogen from these substrates. In addition, unlike other bacteria, ' C. trachomatis' was unable to regulate transcription of central metabolism genes in response to type or amount of carbon found in its growth environment. Information generated from these studies can be used towards the development of new treatments for chlamydial diseases and towards the development of a cell-free growth system for chlamydiae.