Glyco‐engineering in Archaea : differential N‐glycosylation of the S‐layer glycoprotein in a transformed Haloferax volcanii strain

Archaeal glycoproteins present a variety of N-linked glycans not seen elsewhere. The ability to harness the agents responsible for this unparalleled diversity offers the possibility of generating glycoproteins bearing tailored glycans, optimized for specific functions. With a well-defined N-glycosylation pathway and available genetic tools, the haloarchaeon Haloferax volcanii represents a suitable platform for such glyco-engineering efforts. In Hfx. volcanii, the S-layer glycoprotein is modified by an N-linked pentasaccharide. In the following, S-layer glycoprotein N-glycosylation was considered in cells in which AglD, the dolichol phosphate mannose synthase involved in addition of the final residue of the pentasaccharide, was replaced by a haloarchaeal homologue of AglJ, the enzyme involved in addition of the first residue of the N-linked pentasaccharide. In the engineering strain, the S-layer glycoprotein is modified by a novel N-linked glycan not found on this reporter from the parent strain. Moreover, deletion of AglD alone and introduction of the AglJ homologue from Halobacterium salinarum, OE2528R, into the deletion strain resulted in increased biosynthesis of the novel 894 Da glycan concomitant with reduced biogenesis of the pentasaccharide normally N-linked to the S-layer glycoprotein. These findings justify efforts designed to transform Hfx. volcanii into a glyco-engineering 'workshop'.