Mycobacterium tuberculosis Glucosyl-3-Phosphoglycerate Synthase: Structure of a Key Enzyme in Methylglucose Lipopolysaccharide Biosynthesis

Tuberculosis constitutes today a serious threat to human health worldwide, aggravated by the increasing number of identified multi-resistant strains of Mycobacterium tuberculosis, its causative agent, as well as by the lack of development of novel mycobactericidal compounds for the last few decades. The increased resilience of this pathogen is due, to a great extent, to its complex, polysaccharide-rich, and unusually impermeable cell wall. The synthesis of this essential structure is still poorly understood despite the fact that enzymes involved in glycosidic bond synthesis represent more than 1% of all M. tuberculosis ORFs identified to date. One of them is GpgS, a retaining glycosyltransferase (GT) with low sequence homology to any other GTs of known structure, which has been identified in two species of mycobacteria and shown to be essential for the survival of M. tuberculosis. To further understand the biochemical properties of M. tuberculosis GpgS, we determined the three-dimensional structure of the apo enzyme, as well as of its ternary complex with UDP and 3-phosphoglycerate, by X-ray crystallography, to a resolution of 2.5 and 2.7 Å, respectively. GpgS, the first enzyme from the newly established GT-81 family to be structurally characterized, displays a dimeric architecture with an overall fold similar to that of other GT-A-type glycosyltransferases. These three-dimensional structures provide a molecular explanation for the enzyme's preference for UDP-containing donor substrates, as well as for its glucose versus mannose discrimination, and uncover the structural determinants for acceptor substrate selectivity. Glycosyltransferases constitute a growing family of enzymes for which structural and mechanistic data urges. The three-dimensional structures of M. tuberculosis GpgS now determined provide such data for a novel enzyme family, clearly establishing the molecular determinants for substrate recognition and catalysis, while providing an experimental scaffold for the structure-based rational design of specific inhibitors, which lay the foundation for the development of novel anti-tuberculosis therapies

Is obesity associated with reduced health-related quality of life in Latino, black and white children in the community?

OBJECTIVE: Few studies have examined the impact of obesity on health-related quality of life (HRQOL) in non-clinical community samples of children, and methodological limitations have hindered drawing firm conclusions, especially whether the impact is similar across racial/ethnic groups. The present aims were to examine at what levels of non-normal weight, school-aged children experience lower HRQOL and whether this differs among racial/ethnic groups, when controlling for socioeconomic status (SES) differences. DESIGN: Cross-sectional community cohort survey. SUBJECTS AND METHODS: Data are from the Healthy Passages, reporting on 4824 Latino, black and white 5th graders in a population-based survey conducted in three United States metropolitan areas. Children's weight status was classified from measured weight and height into underweight (1%), normal weight (52%), overweight (19%), obese (13%) and extremely obese (14%). Children reported their own HRQOL using the Pediatric Quality of Life Inventory and additional scales addressing global self-worth, physical appearance and body satisfaction. Parents reported children's overall health status. RESULTS: Each increment in higher non-healthy weight class—overweight to obese to extremely obese—was associated with significantly lower scores in more domains of psychosocial HRQOL compared with that in normal weight. However, only extremely obese children reported significantly lower physical HRQOL. Differences among weight classes remained when adjusting for SES and were independent of race/ethnicity. Underweight children generally reported HRQOL that was not significantly different from normal weight children. CONCLUSIONS: Overweight, obese and extremely obese 5th graders on average experience worse HRQOL than normal weight children, especially in psychosocial domains including self-worth and peer relationships, regardless of race/ethnicity. If messages can be conveyed in a sensitive and supportive manner, the desire to improve HRQOL could provide additional motivation for children and their parents in addressing unhealthy weight

Octanoylation of early intermediates of mycobacterial methylglucose lipopolysaccharides

Mycobacteria synthesize unique intracellular methylglucose lipopolysaccharides (MGLP) proposed to modulate fatty acid metabolism. In addition to the partial esterification of glucose or methylglucose units with short-chain fatty acids, octanoate was invariably detected on the MGLP reducing end. We have identified a novel sugar octanoyltransferase (OctT) that efficiently transfers octanoate to glucosylglycerate (GG) and diglucosylglycerate (DGG), the earliest intermediates in MGLP biosynthesis. Enzymatic studies, synthetic chemistry, NMR spectroscopy and mass spectrometry approaches suggest that, in contrast to the prevailing consensus, octanoate is not esterified to the primary hydroxyl group of glycerate but instead to the C6 OH of the second glucose in DGG. These observations raise important new questions about the MGLP reducing end architecture and about subsequent biosynthetic steps. Functional characterization of this unique octanoyltransferase, whose gene has been proposed to be essential for M. tuberculosis growth, adds new insights into a vital mycobacterial pathway, which may inspire new drug discovery strategies