New structural insights into the molecular deciphering of mycobacterial lipoglycan binding to C-type lectins: Lipoarabinomannan glycoform characterization and quantification by capillary electrophoresis at the subnanomole level

Lipoarabinomannans are key molecules of the mycobacterial envelopes involve d in many steps of tuberculosis immunopathogenesis. Several of the biologic al activities of lipoarabinomannans are mediated by their ability to bind h uman C-type lectins, such as the macrophage mannose receptor, the mannose-b inding protein and the surfactant proteins A and D. The lipoarabinomannan m annooligosaccharide caps have been demonstrated to be involved in the bindi ng to the lectin carbohydrate recognition domains. We report an original an alytical approach, based on capillary electrophoresis monitored by laser-in duced fluorescence, allowing the absolute quantification, in nanomole quant ities of lipoarabinomannan, of the number of mannooligosaccharide units per lipoarabinomannan molecule. Moreover, this analytical approach was success ful for the glycosidic linkage determination of the mannooligosaccharide mo tifs and has been applied to the comparative analysis of parietal and cellu lar Lipoarabinomannans of Mycobacterium bovis BCG and Mycobacterium tubercu losis H37Rv, H37Ra and Erdman strains. Significant differences were observe d in the amounts of the various mannooligosaccharide units between lipoarab inomannans of different strains and between parietal and cellular lipoarabi nomannans of the same strain. Nevertheless, no relationship was found betwe en the number of mannooligosaccharide caps and the virulence of the corresp onding strain. The results of the present study should help us to gain more understanding of the molecular basis of Lipoarabinomannan discrimination i n the process of binding to C-type lectins. (C) 2000 Academic Press.