ENZYMATIC EVIDENCE FOR THE PRESENCE OF A CRITICAL TERMINAL HEXA-ARABINOSIDE IN THE CELL-WALLS OF MYCOBACTERIUM-TUBERCULOSIS

A species of Cellulomonas was isolated from soil by enrichment culture and shown to secrete enzymes capable of degrading mycobacterial cell wall arabinogalactan, both the insoluble peptidoglycan-bound and base- solubilized forms. The major degradation product was purified and char acterized as a hexa-arabinofuranoside, -Araf-(1-->](2)-->3,5-alpha-D-A raf-(1-->5)-D-Araf. The non-reducing ends of this unit are the sites o f mycolic acid attachment and, as they also appear in lipoarabinomanna n (LAM), the point of mannose capping in some mycobacteria. Thus, elab oration of the structure of this focal hexasaccharide is critical to o ur understanding of much of the physiology and pathogenesis of mycobac teria. The extracellular enzymes of Cellulomonas sp. also released the disaccharide, alpha-D-Araf-(1-->5)-D-Araf, from internal linear regio ns of arabinan and, surprisingly, convert the linear galactan backbone into cyclic oligosaccharides of the structure [-->5-D-Galf-(1-->6)-be ta-D-Galf(1--> ](n) where n is 2, 3 or 4. Thus, the preparation contai ns Schardinger-like enzyme activity. This group of enzymes are powerfu l tools for the dissection of the mycolylarabino-galactan-peptidoglyca n (mAGP) complex of mycobacteria towards understanding its role in dru g resistance, disease processes and mycobacterial physiology.