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Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a major pathogen responsible for 1.5 million deaths annually. This bacterium is characterized by a highly unusual and impermeable cell envelope, which plays a key role in mycobacterial survival and virulence. Although many studies have focused on the composition and functioning of the mycobacterial cell envelope, the capsular α-glucan has received relatively minor attention. Here we show that a murine monoclonal antibody (Mab) directed against glycogen cross-reacts with mycobacterial α-glucans, polymers of α(1-4)-linked glucose residues with α(1-6)-branch points. We identified the Mab epitope specificity by saturation transfer difference NMR and show that the α(1-4)-linked glucose residues are important in glucan-Mab interaction. The minimal epitope is formed by (linear) maltotriose. Notably, a Mycobacterium mutant lacking the branching enzyme GlgB does not react with the Mab; this suggests that the α(1-6)-branches form part of the epitope. These seemingly conflicting data can be explained by the fact that in the mutant the linear form of the α-glucan (amylose) is insoluble. This Mab was subsequently used to develop several techniques helpful in capsular α-glucan research. By using a capsular glucan-screening methodology based on this Mab we were able to identify several unknown genes involved in capsular α-glucan biogenesis. Additionally, we developed two methods for the detection of capsular α-glucan levels. This study therefore opens new ways to study capsular α-glucan and to identify possible targets for further research.

facile accretion.34 Cd(II) complexes with yEC peptides longer than = 4 are predicted to be less effective in nucleating CdS crystallite formation perhaps by virtue of enhanced stability of Cd-cysteinyl thiolate clusters. The importance of sulfide in metal detoxification is highlighted by the isolation of sulfide-deficient S. pombe mutants that exhibit cadmium hypersensitivity.15The increased stability of S. pombe CdS crystallites does not imply that 5. pombe is more resistant to cadmium salts than C.glabrata. The yeast C. glabrata is highly resistant to toxicity of cadmium salts. Formation of CdS crystallites is only one cellular detoxification mechanism in this organism. The other mechanisms have not been elucidated.The crystallites exhibit properties analogous to those of semiconductor clusters. The yeast CdS particles are quantum crystallites that luminesce and mediate electron transfer to methyl viologen. The latter two properties are attributed to the localization of excited electrons on the surface of the particles.31 Luminescence in synthetic CdS semiconductor clusters is attributed to the recombination of a photogenerated electron and an existing hole.28 The electronic state of the electron is not apparent in the absorption spectrum.28 Luminescence correlates with particle size and is influenced by surface adsorbed cations. Cations are known (34) Dameron, C. T.; Winge, D. R. J. Biol. Chem., in press.to quenched the luminescence of synthetic colloidal CdS.30 The effect is attributed to electron scavenging at the surface of the particles. Electrons are also scavenged by methyl viologen at the surface. Under anaerobic conditions, the reduced dye is stable against facile oxidation, but a significant back-reaction occurs that is attributed to reoxidation of the dye by trapped holes (h+) in the particle.30 The presence of hole scavengers has been shown to inhibit this route of oxidation in some but not all studies.35•36 Crystallites formed in vitro with yEC peptides exhibit corresponding excited electronic state properties.The effectiveness of 7EC peptides in stabilizing discrete sizes of CdS crystallites either in vivo or in vitro may enable the peptides to be used as a matrix for other types of mineralization where discrete particle size is desired. As metal-sulfide clusters are used as photosensitizing and catalytic agents,30•37 discrete sizes of these quantum particles may yield more predictable properties. Presently, synthetic semiconductor clusters are typically coated with nonspecific organic polymers, leading to a wide spectrum of particle sizes.