Mycobacterium tuberculosis β-gentiobiosyl diacylglycerides signal through the pattern recognition receptor Mincle: total synthesis and structure activity relationships

Abstract

Mycobacterium tuberculosis H37Ra produces a range of immunogenic β-gentiobiosyl diacylglycerides. We report the total synthesis of several candidate structures and show that these compounds signal weakly through mouse, but not human, Mincle. Structure-activity relationships reveal a striking dependence upon acyl chain length for gentiobiosyl diacylglyceride signalling through Mincle. Significantly, a truncated β-glucosyl diglyceride was shown to provide potent signalling through both human and mouse Mincle and could activate murine bone marrow derived dendritic cells.

Intracellular metabolite β-glucosylceramide is an endogenous Mincle ligand possessing immunostimulatory activity

“…As another example, epidermis has a unique GlcCer epidermoside, which is composed of a longer unsaturated ω-hydroxy FA that functions to maintain the epidermal permeability barrier (39,40). Given that glycolipids with longer FA have potent activities (10,11,34,35), epidermosides might be recognized by Mincle on dermal Mϕ/DCs and thereby modulate immune responses in skin. Interestingly, Mincle is involved in the immune response against fungi that causes skin disease (41) through the recognition of its unique glycolipids (7,42).…”

“…A common Mincle ligand signature structure has been predicted based on a number of identified ligands (6,7,(33)(34)(35) in combination with the Mincle protein structure (9)(10)(11)(12). A polar head consisting of glucose or mannose and a hydrophobic chain appear to be the minimum requirement for ligand activity.…”

Sensing Lipids with Mincle: Structure and Function

“…A related series of gentiobiosides were isolated by Brennan and co-workers from M. tuberculosis H37Ra ( 56 ). In order to determine whether these compounds can signal through Mincle, Williams and co-workers synthesized a series of related gentiobiosides representing those isolated, namely four lipoforms bearing C 18 , iso-C 17 , iso-C 18 , and iso-C 19 fatty acids (Figure 5 B) ( 57 ). Like the Malassezia gentiobiosides, all four lipoforms signaled only weakly through mouse Mincle and did not signal through human Mincle.…”

Quantitation in the regioselectivity of acylation of glycosyl diglycerides: total synthesis of a Streptococcus pneumoniae α-glucosyl diglyceride

“…In previous work, we prepared a range of glycosyl diglycerides including b-gentiobiosyl diglycerides, 15 a-glucosyl diglycerides, 16 and a-glucuronosyl diglycerides. 11 We consistently observed a chemical shift difference for the carbonyl group of an ester attached as a primary ester at the glycerol sn-1 position (d B 173 ppm), versus a secondary ester at the sn-2 position (d B 172.5 ppm), which was independent of the length of or functionalization within the fatty acyl chain.…”

“…Using a representative glycosyl diglyceride from previous work (1,2-di-O-[13-methyltetradecanoyl]-sn-glyceryl-2,3,4,6-tetra-O-benzyl-b-D-glucopyranoside) 15 T 1 relaxation times of the ester carbonyls were estimated using the sign-inversion recovery method. 17 In the absence of PRE agent, carbonyl 13 C T 1 relaxation times of around 15 s were observed; however, in samples containing 0.05 M Cr(acac) 3 T 1 relaxation times were reduced to 0.5-1.0 s, comparable to published values.…”