Characterization of the in vitro synthesized arabinan of mycobacterial cell walls

Previous studies have shown that polymerized [C-14]arabinan can be synthesized from polyprenylphosphate-[C-14]arabinose by the particulate enzymes of Mycobacterium smegmatis [R.E. Lee, K. Mikusova, P.J. Brennan and G.S Besra (1995) J. Am. Chem. Sec. 117, 11829-11832]. In the present investigation, the [C-14]arabinan product was biochemically characterized. Sizing chromatography revealed a molecular weight consistent with that expected from mature arabinan. Digestion of the [C-14]arabinan with a mixture of arabinases produced oligo[C-14]arabinoside fragments including hexa[C-14]arabinoside and tetra[C-14]arabinoside which originated from the non-reducing terminal regions of the polymer, and di[C-14]arabinoside from the internal regions of the polymer. These arabinoside fragments represent the major known structural motifs that comprise the arabinan segment of arabinogalactan and lipoarabinomannan. The presence of [C-14]arabinose in both the internal and external regions of the [C-14]arabinan suggests that polyprenylphosphate-arabinose is the major, and perhaps the only, donor of arabinosyl residues in mycobacteria.