Youderian The predatory Gram-negative bacterium, Myxococcus xanthus, derives its metabolic energy primarily from the oxidation of amino acids. This species is the best-characterized representative of the Myxobacteria, the only group of bacteria that respond to starvation (for proteins) by undergoing a program of multicellular development. Previous studies suggested that M. xanthus does not have a "sweet tooth". That is, simple hexose sugars including glucose do not stimulate its growth, even on defined medium. However, M. xanthus is sensitive to the glucose analogue, 2-deoxyglucose (2dGIc). This antibiotic is toxic, because it is phosphorylated by hexokinase, the first enzyme in the primary glycolytic pathway for sugar catabolism present in most organisms that utilize glucose. The isolation and characterization of spontaneous mutants of M. xanthus resistant to 2dGIc shows that M. xanthus makes a hexokinase and must transport simple sugars. This hexokinase is unusual, because it is inhibited by the two essential hexosamine sugars glucosamine and N-acetylglucosamine. Another bacterial hexokinase, made by E. coil, is also inhibited by the same sugars. The three main goals of this research are: (1) to understand why these enzymes are sensitive to 2dGIc and inhibited by hexosamines; (2), to identify the precise target of 2dGIc-6-phosphate responsible for the toxicity of 2dGIc in most organisms; and (3) to understand the regulatory mechanism in this organism that governs the preference for amino acids over glucose. To accomplish the first task, the kinetics of substrate binding and utilization of these sugars by hexokinase will be examined using kinetic and mechanistic approaches. The hexokinase gene from M. xanthus will be cloned and sequenced, and both the M. xanthus and E. coil enzymes will be purified. Second, the recent discovery that the production of intracellular 2dGIc-6-phosphate results in the depletion of ATP in M. xanthus, as it does in mammalian cells, has led to the search for the critical enzyme involved in central carbon metabolism specifically inhibited by low concentrations of 2dGIc-6-phosphate, again using traditional biochemical tactics. Third, glucose catabolism in M. virescens, which oxidizes glucose readily, and in M. xanthus, which may not, will be compared.
Many living organisms, like humans, burn sugars for energy, but prefer a rich protein diet. The soil bacterium, Myxococcus xanthus, chooses a protein-rich diet ("steak") over a carbohydrate-rich diet ("potatoes") to an extreme, because sugar doesn't stimulate its growth. The goal of this research is to understand why some individual organisms have this kind of dietary preference. Biochemical studies show that the steak-loving bacterium M. xanthus can still taste sugars, because it is fooled by the sweet poison of 2-deoxyglucose, which tastes like sweet glucose-rich Gatorade TM, but has the opposite effect. This poison, 2-deoxyglucose, has been known to be toxic to most living things for 50 years. No one really understands why, except for the finding that it drains ATP (energy) levels in many living cells, including M. xanthus. M. xanthus will be used as a model organism to figure out why this poison is a poison, and, at the same time, gain fundamental insights at a basic chemical level about how organisms choose what to eat.