Development of a trehalose 6,6'-dimycolate model which explains cord formation by Mycobacterium tuberculosis.

Trehalose 6,6'-dimycolate (TDM) is a glycolipid of mycobacteria that displays an unusual toxicity and has been reported to be a virulence factor for Mycobacterium tuberculosis. Lack of understanding of the toxicity has impeded acceptance of TDM as a virulence factor. We previously reported that the toxicity of TDM depends on its presentation as a surface monolayer consisting of 30% trehalose and 70% exposed mycolic acid moieties. This paper further investigates the structure of the TDM monolayer. It began with the observation that beads coated with TDM, but not with closely related analogs, aggregate to form organized structures resembling the cords of virulent mycobacteria. This implied that the TDM molecules in the monolayer were arranged in an organized structure. This structure was investigated by real-time kinetic microscopy, scanning electron microscopy, and gross observations of the adhesion patterns of TDM-coated beads. In each of these models, the structures induced by TDM differed from those of analogs or other amphiphiles studied. These observations were used to construct a model of the structure of TDM monolayer which envisions linear arrays of TDM molecules arranged in a circumferential pattern on beads with discontinuities only at the two poles.