Structural features of the arabinan component of the lipoarabinomannan of Mycobacterium tuberculosis

D Chatterjee,C.M Bozic,M Mcneil,P.J Brennan

doi:10.1016/s0021-9258(18)92870-x

D Chatterjee, C.M Bozic + Show 2 more

Open Access

https://doi.org/10.1016/s0021-9258(18)92870-x

Copy DOI

Abstract

The recent availability of pure lipoarabinomannan (LAM) from Mycobacterium spp. has resulted in its implication in host-parasite interaction, which events may be mediated by the presence of a phosphatidylinositol unit at the reducing end of LAM. Herein we address the structure of the antigenic, nonreducing end of the molecule. Through the process of 13C NMR analysis of the whole molecule and gas chromatography/mass spectrometry of alditol acetates derived from the differential per-O-alkylated lipopolysaccharide, the majority of the arabinosyl residues were recognized as furanosides. Second, through analysis of per-O-alkylated oligoarabinosyl arabinitol fragments of partially hydrolyzed LAM, it was established that the internal segments of the arabinan component consists of branched 3,5-linked alpha-D-arabinofuranosyl (Araf) units with stretches of linear 5-linked alpha-D-Araf residues attached at both branch positions, whereas the nonreducing terminal segments of LAM consist of either of the two arrangements, beta-D-Araf-(1----2)-alpha-D-Araf-(1----5)- alpha-D-Araf---- or [beta-D-Araf-(1----2)-alpha-D-Araf-(1----]2---- (3 and 5)-alpha-D-Araf----. Since this latter arrangement also characterizes the terminal segments of the peptidoglycan-bound arabinogalactan of Mycobacterium spp., we propose that mycobacteria elaborate unique terminal arabinan motifs in two distinct settings. In the case of the bound arabinogalactan, these motifs provide the nucleus for the esterified mycolic acids, entities which dominate the physicochemical features of mycobacteria and their peculiar pathogenesis. In the case of LAM, these motifs, non-mycolylated, are the dominant B-cell antigens responsible for the majority of the copious antibody response evident in most mycobacterial infections.

Highlights

The recent availability of pure lipoarabinomannan antigenic, excreted in copious quantities, and with many of (LAM) from Mycobacterium spp. has resulted in its the biological attributes long associated with the likes of the implication in host-parasite interaction, which events 0-antigenic lipopolysaccharides (l),such as suppression of T - may be mediated by the presence of a phosphatidyl- lymphocyte activation [2, 3], inhibition of y-interferon actiinositol unit at the reducing end ofLAM
Since thislatter arrange- The older literature hadclearly demonstrated that the arabiment characterizes the terminal segments of the nan segments of LAM were the basis of its profound B-cell peptidoglycan-bound arabinogalactan of Mycobacte- antigenicity in that serological activity was ablated by the rium spp., we propose that mycobacteriaelaborate action of endoarabinases and mildacidhydrolysis [12, 13] unique terminal arabinan motifs in two distinct set- and the fact that lipomannan, essentially an arabinose-free tings
Motifs provide the nucleus for the esterified mycolic we address theissue of the structural basisof the antigenicity eafmamescroaiaeisdsjt.otutsIhrm,rneieetnyystdtcoihoootfiefmbemastihccwyntaecaehosnoricefictboahBaLpldcA-iotiocenMmeurflsie,litanchaatanenaitstotneiienbtgdhsoem.endthsyoetrriiefersssp,pppooenhnncoyssuniselb-iicmleaeovrycficodhporeealnmttyhhtlieoaicntgaeledn, -bpmos(1ofeaa5mpsLji)toAsei.drWoiMootffyg,e,tlwyhwsrhcepehavieecndecnh-aoublmlhioanaauitgpdennpadtnbehnDoaeatv-retiaiemntnrlhargmeeboascuilnesoingogtooh-ngDameiezr-ntaoegebidtacriimflinpastoyrcipefntruvaoaonriflvoaniLnudoosAeolnsyMfyraelta,mhrdsrewuyacsncphitogeanrbrerugeatmcaoctsfetusenttrerhhtaigsaeel, ments of arabinogalactan, provide the templatesfor esterified mycolic acid, theoneentitythatdominatesthe physical properties of mycobacteria, their peculiar pathogenesis and Within Mycobacterium spp. there existas dominant soluble persistence. polysaccharide, termedlipoarabinomannan(LAM),’ highly

Summary

Introduction

The recent availability of pure lipoarabinomannan antigenic, excreted in copious quantities, and with many of (LAM) from Mycobacterium spp. has resulted in its the biological attributes long associated with the likes of the implication in host-parasite interaction, which events 0-antigenic lipopolysaccharides (l),such as suppression of T - may be mediated by the presence of a phosphatidyl- lymphocyte activation [2, 3], inhibition of y-interferon actiinositol unit at the reducing end ofLAM. Purification of LAM-The isolation of LAM-containing fractions from Mycobacterium tuberculosis H37Ra and primary resolution on columns of DEAE-Sephacel in detergent-containing buffehrave been described [9, 10]. To these steps, preparationosf LAM, recovered from columnsof DEAE-Sephacel andhighly pure according to polyacrylamide gel electrophoresis [9],were dialyzed, concentrated on anAmicon flow cell (Amicon 8200; Danvers, MA; 10kDa molecular mass cut-off membrane), precipitated with 85% ethanol, redissolved in 0.01 M TrisHCl(pH 7.4) containing 0.1% Triton X-100 and applied to a HYDROPORE AX HPLC column (121.4 mm x 25 cm, Rainin, Woburn, MA) equilibrated in the same buffer. Pure LAM obtained was the subject of the analyses described below

Methods

Results

Conclusion