Which glycosidic bond is found in the pseudomurein of archaea?
Glycosidic bond specificity determines susceptibility to host defenses and bacteriophages. Bacterial peptidoglycan uses beta-1,4 linkages between N-acetylglucosamine and N-acetylmuramic acid, a substrate efficiently cleaved by hen egg white lysozyme and human lysozyme in tears and mucus, which hydrolyzes between C1 of MurNAc and C4 of GlcNAc. Archaeal pseudomurein in methanogens such as Methanobacterium and Methanobrevibacter employs beta-1,3 linkage between N-acetylglucosamine and N-acetyltalosaminuronic acid. This change in linkage position alters orientation of sugar residues and active site complementarity, rendering bond refractory to lysozyme and to many bacterial autolysins that recognize beta-1,4. Alpha-linked variants such as alpha-1,4 found in starch and alpha-1,6 in glycogen are characteristic of storage polysaccharides, not wall polymers. Beta-1,3 linkage also affects cell wall flexibility and recognition by innate immune lectins. Hence presence of beta-1,3 rather than beta-1,4 is diagnostic feature underlying lysozyme resistance of pseudomurein-containing archaea and informs use of pseudomurein-specific endopeptidases like PeiW. Structural modeling demonstrates altered distance between anomeric carbons, affecting hydrogen bonding network that stabilizes wall, and this change has biotechnological implication because pseudomurein-specific hydrolases are used as tools for archaeal cell wall disruption in laboratories studying methanogenesis and for controlling bloating in ruminant animals.
Ref: Sekh et al., Extremophiles 2020, Pseudomurein Linkages; Leahy et al., Front Microbiol 2020, Archaeal Wall.