Structural elucidation of novel methylglucose-containing polysaccharides from Mycobacterium xenopi.

The structures of methylglucose-containing polysaccharides (MeGlc PS) from Mycobacterium xenopi were investigated using high-pH anion-exchange chromatography and liquid secondary-ion mass spectrometry. We report the structure of two novel MeGlc PS, referred to as A and B. MeGlc PS A is composed of 16 D-glucopyranose residues, 11 of which are methylated, and MeGlc PS B contains 15 D-glucopyranose residues, 10 of which are methylated. The main structural feature of both MeGlc PS A and B, compared to the previously described structures, is the absence of the tetrasaccharide non-reducing end 3-O-Me-D-Glcp-[alpha(1-->4)-D-Glcp]3. The MeGlc PS A structure is similar to the synthetic polysaccharide [Saïer, M. H. & Ballou, C. E. (1968) J. Biol. Chem. 243, 992-1005], having a lower affinity for fatty acids than the MeGlc PS of Mycobacterium smegmatis [Kiho, T. & Ballou, C. E. (1988) Biochemistry 27, 5824-5828]. Thus, the occurrence of MeGlc PS A and the consequences on the regulation of fatty acid synthetase I activity involved in the biosynthesis of fatty acids, precursors of mycolic acid biosynthesis, is discussed.