Polysaccharide length affects mycobacterial cell shape and antibiotic susceptibility

Abstract

Bacteria control the length of their polysaccharides, which can control cell viability, physiology, virulence, and immune evasion. Polysaccharide chain length affects immunomodulation, but its impact on bacterial physiology and antibiotic susceptibility was unclear. We probed the consequences of truncating the mycobacterial galactan, an essential linear polysaccharide of about 30 residues. Galactan covalently bridges cell envelope layers, with the outermost cell wall linkage point occurring at residue 12. Reducing galactan chain length by approximately half compromises fitness, alters cell morphology, and increases the potency of hydrophobic antibiotics. Systematic variation of the galactan chain length revealed that it determines periplasm size. Thus, glycan chain length can directly affect cellular physiology and antibiotic activity, and mycobacterial glycans, not proteins, regulate periplasm size.

An ABC transporter Wzm–Wzt catalyzes translocation of lipid-linked galactan across the plasma membrane in mycobacteria

“…S7), which corresponds to the expected GlcNAc-Rha-Gal n oligosaccharide. Intriguingly, the sum of the presumed galactosyl monomers, as established by MALDI-TOF MS, ranged from ∼40 to more than 50 residues, which largely exceeds the number of Galf units in the mature mycolyl-arabinogalactan complex recently established to contain ∼35 Galf residues in Msm (39). On the other hand, an examination of the E-soak extract from Msm PLJR962-wzm SM grown without ATc showed almost negligible amounts of the α-naphthol-positive material in the fractions from gel filtration.…”

Progress and challenges in the synthesis of sequence controlled polysaccharides

“…Exploitation of polysaccharides has always relied on mixtures of compounds extracted from natural sources. Much effort has been put to understand how sequence, length, and substitution pattern affect polysaccharides’ biological and material properties [ 93 , 221 , 350 ]. Therefore, well-defined polysaccharide samples become essential probes to establish structure–property correlations and for reproducible biological studies [ 93 , 221 , 350 ].…”

“…Much effort has been put to understand how sequence, length, and substitution pattern affect polysaccharides’ biological and material properties [ 93 , 221 , 350 ]. Therefore, well-defined polysaccharide samples become essential probes to establish structure–property correlations and for reproducible biological studies [ 93 , 221 , 350 ]. Polysaccharides with well-defined chemical structures can be prepared synthetically following three main approaches: i) enzymatic methods, ii) polymerization, and iii) chemical synthesis.…”

“…The cell wall of mycobacteria contains galactofuranose (Gal f )-based polysaccharides that play various functional roles based on their length [ 350 ]. These polymers are biosynthesized in a length-controlled manner by complex enzymatic machineries.…”

“…The mechanism of galactan length control may differ consistently between the in vitro and in vivo setting as the interplay between the GlfT2 enzyme, the plasma membrane and other proteins involved in transport across the membrane play a crucial role in length control [ 353 – 354 ]. Recently, it was reported that a mutation on the GlfT2 enzyme enabled the regulation of the galactan chain length (4mer or 11mer with a relatively narrow distribution) [ 350 ]. These examples suggest a potential avenue to produce length-controlled polysaccharides via glycoengineering [ 351 , 354 – 355 ].…”