Arabinogalactan

The mycobacterial arabinogalactan is recognized by a putative immune lectin intelectin present in chordates.

[6] The reducing end of microbial arabinogalactan consists of the terminal sequence →5)-D-Galf-(1→4)-L-Rhap-(1→3)-D-GlcNAc[citation needed].

[3] The non-reducing end of arabinogalactan is covalently attached to the mycolic acids of the outer membrane.

The mycolyl substituents are selectively and equally distributed on the 5-hydroxyl functions of terminal- and the penultimate 2-linked Araf residues.

The mycolyl residues are clustered in groups of four on the non reducing terminal pentaarabinosyl unit (β-Araf-(1→2)-α-Araf)2-3,5-α-Araf .

Thus, the majority (66%) of the pentaarabinosyl units are substituted by mycolic acids, leaving the minority (33%) available for interaction with the immune system.