Mannan core branching of lipo(arabino)mannan is required for mycobacterial virulence in the context of innate immunity

Esther J M Stoop,Nicole N Driessen,Maaike Van Zon,Gurdyal S Besra,Wilbert Bitter,Pascale Bouchier,Nicole N Van Der Wel,Lisanne M Van Leeuwen,Gunny Van Stempvoort,Arun K Mishra,Theo Verboom,Astrid M Van Der Sar,Susanne A Raadsen,Ben J Appelmelk,Jeroen Geurtsen,Marion Sparrius

doi:10.1111/cmi.12175

Abstract

The causative agent of tuberculosis (TB), Mycobacterium tuberculosis, remains an important worldwide health threat. Although TB is one of the oldest infectious diseases of man, a detailed understanding of the mycobacterial mechanisms underlying pathogenesis remains elusive. Here, we studied the role of the α(1→2) mannosyltransferase MptC in mycobacterial virulence, using the Mycobacterium marinum zebrafish infection model. Like its M. tuberculosis orthologue, disruption of M. marinum mptC (mmar_3225) results in defective elongation of mannose caps of lipoarabinomannan (LAM) and absence of α(1→2)mannose branches on the lipomannan (LM) and LAM mannan core, as determined by biochemical analysis (NMR and GC-MS) and immunoblotting. We found that the M. marinum mptC mutant is strongly attenuated in embryonic zebrafish, which rely solely on innate immunity, whereas minor virulence defects were observed in adult zebrafish. Strikingly, complementation with the Mycobacterium smegmatis mptC orthologue, which restored mannan core branching but not cap elongation, was sufficient to fully complement the virulence defect of the mptC mutant in embryos. Altogether our data demonstrate that not LAM capping, but mannan core branching of LM/LAM plays an important role in mycobacterial pathogenesis in the context of innate immunity.

Highlights

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a successful pathogen which has infected approximately one-third of the world’s population (Dye et al, 1999)
We studied the role of the α(1→2) mannosyltransferase MptC in mycobacterial virulence, using the Mycobacterium marinum zebrafish infection model
LAM can be devoid of any capping motif, resulting in AraLAM such as in Mycobacterium chelonae cellular microbiology (Guerardel et al, 2002), capped by phosphoinositol (PI) units leading to PILAM as found in Mycobacterium smegmatis (Khoo et al, 1995), or further modified by manp capping units resulting in ManLAM as is the case in M. tuberculosis and Mycobacterium marinum (Appelmelk et al, 2008; Kaur et al, 2008)

Summary

Introduction

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a successful pathogen which has infected approximately one-third of the world’s population (Dye et al, 1999). The lipid rich cell envelope serves as a template for glycoconjugates, such as phosphatidyl-myo-inositol mannosides (PIMs), lipomannan (LM) and lipoarabinomannan (LAM) (Briken et al, 2004; Mishra et al, 2011a). PIMs are composed of a mannosylphosphatidyl-myo-inositol (MPI) anchor substituted with one to five mannose residues (PIM1 to PIM6). LM probably serves as a precursor of LAM that is further glycosylated by arabinan residues leading to a highly branched arabinan domain (Birch et al, 2010; Alderwick et al, 2011) (Fig. S1). Mannose caps of ManLAM vary in length and consist of a single α(1→5)-manp that can be elongated with one or two α(1→2)-manp units (Besra et al, 1997; Nigou et al, 2003) (Fig. S1)

Results

Discussion

Conclusion