Substrate Promiscuity: AglB, the Archaeal Oligosaccharyltransferase, Can Process a Variety of Lipid-Linked Glycans

Abstract

ABSTRACTAcross evolution, N-glycosylation involves oligosaccharyltransferases that transfer lipid-linked glycans to selected Asn residues of target proteins. While these enzymes catalyze similar reactions in each domain, differences exist in terms of the chemical composition, length and degree of phosphorylation of the lipid glycan carrier, the sugar linking the glycan to the lipid carrier, and the composition and structure of the transferred glycan. To gain insight into how oligosaccharyltransferases cope with such substrate diversity, the present study analyzed the archaeal oligosaccharyltransferase AglB from four haloarchaeal species. Accordingly, it was shown that despite processing distinct lipid-linked glycans in their native hosts, AglB fromHaloarcula marismortui,Halobacterium salinarum, andHaloferax mediterraneicould readily replace their counterpart fromHaloferax volcaniiwhen introduced intoHfx. volcaniicells deleted ofaglB. As the four enzymes show significant sequence and apparently structural homology, it appears that the functional similarity of the four AglB proteins reflects the relaxed substrate specificity of these enzymes. Such demonstration of AglB substrate promiscuity is important not only for better understanding of N-glycosylation inArchaeaand elsewhere but also for efforts aimed at transformingHfx. volcaniiinto a glycoengineering platform.