Keywords : phosphotransferase system, inducer expulsion, carbon and energy metabolism OverviewOver the past quarter of a century, tremendous effort has allowed elucidation of crucial aspects of the mechanisms of catabolite repression and cytoplasmic inducer control in Escherichia coli and other Gram-negative enteric bacteria (Botsford & Harman, 1992;Postma et al., 1993; Saier, 1989Saier et al., 1996). The extent of this effort reflected in part the belief that 'What is true for E. coli is also true for elephants' (J. Monod), and that the mechanism observed for E. coli would therefore prove to be universal. The observation that catabolite repression and inducer exclusion (Magasanik, 1970) are universal phenomena, documented in phylogenetically distant bacteria as well as in eukaryotes, seemed to substantiate this suggestion . Early investigations consequently focused on E. coli for a detailed understanding of the mechanisms involved. More recently, several research groups have begun to examine the mechanisms controlling carbohydrate catabolism in bacteria other than E. coli. In most cases, clear mechanistic concepts have not yet crystallized. However, in one group of prokaryotes, the low-GC Gram-positive bacteria, crucial aspects of the underlying mechanism are emerging. The proposed mechanism involves the proteins of the phosphoenolpyruvate (PEP)-dependent sugar transporting phosphotransferase system (PTS) as in E. coli, but the proteins that are directly involved in regulation and the mechanisms responsible for this control are completely different. This review provides a synopsis of recent advances concerned with the details of this process. The bacterial phosphotransferase system catalyses the concomitant uptake and phosphorylation (group translocation) of its sugar substrates (PTS sugars) via the PTS phosphoryl transfer chain as follows : PEP + Enzyme I + HPr + Enzyme IIASUg"' + Enzyme IIBCSUgar + sugar-P Virtually all low-GC Gram-positive bacteria that have been examined, including species of Bacilhs, Stapbylococczis, Streptococczrs, Lactococcus, Lactobacillzrs, Enterococczrs, Mycoplasma, Acboleplasma, Clostridizrm and Listeria, possess the enzymes of the PTS. In select Gram-positive bacteria, glucose has been shown to repress synthesis of both PTS and non-PTS carbohydrate catabolic enzymes ; it also inhibits the uptake of both PTS and non-PTS sugars (inducer exclusion) while stimulating dephosphorylation of intracellular sugar-Ps and/or efflux of the free sugars (inducer expulsion) (Fig. 1). Substantial evidence supports the contention that a metabolite-activated ATP-dependent protein kinase phosphorylates a seryl residue in HPr to regulate enzyme synthesis, inducer exclusion and inducer expulsion. A single allosteric regulatory mechanism acting on different target proteins is probably involved (Deutscher e t

The structure of Clostridium thermocellum endoglucanase CelC, a member of the largest cellulase family (family A), has been determined at 2.15 A resolution. The protein folds into an (alpha/beta)8 barrel, with a deep active-site cleft generated by the insertion of a helical subdomain. The structure of the catalytic core of xylanase XynZ, which belongs to xylanase family F, has been determined at 1.4 A resolution. In spite of significant differences in substrate specificity and structure (including the absence of the helical subdomain), the general polypeptide folding pattern, architecture of the active site and catalytic mechanism of XynZ and CelC are similar, suggesting a common evolutionary origin.

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Rhodococcus ruber (formerly