Haloferax volcanii N-glycosylation: delineating the pathway of dTDP-rhamnose biosynthesis.
In the halophilic archaea Haloferax volcanii, the surface (S)-layer glycoprotein can be modified by two distinct N-linked glycans. The tetrasaccharide attached to S-layer glycoprotein Asn-498 comprises a sulfated hexose, two hexoses and a rhamnose. While Agl11-14 have been implicated in the appearance of the terminal rhamnose subunit, the precise roles of these proteins have yet to be defined. Accordingly, a series of in vitro assays conducted with purified Agl11-Agl14 showed these proteins to catalyze the stepwise conversion of glucose-1-phosphate to dTDP-rhamnose, the final sugar of the tetrasaccharide glycan. Specifically, Agl11 is a glucose-1-phosphate thymidylyltransferase, Agl12 is a dTDP-glucose-4,6-dehydratase and Agl13 is a dTDP-4-dehydro-6-deoxy-glucose-3,5-epimerase, while Agl14 is a dTDP-4-dehydrorhamnose reductase. Archaea thus synthesize nucleotide-activated rhamnose by a pathway similar to that employed by Bacteria and distinct from that used by Eukarya and viruses. Moreover, a bioinformatics screen identified homologues of agl11-14 clustered in other archaeal genomes, often as part of an extended gene cluster also containing aglB, encoding the archaeal oligosaccharyltransferase. This points to rhamnose as being a component of N-linked glycans in Archaea other than Hfx. volcanii.
Department of Life Sciences, Ben Gurion University, Beersheva, Israel.
Lina
L
Kaminski
Department of Life Sciences, Ben Gurion University, Beersheva, Israel.
Jerry
J
Eichler
D019843:Archaeal Proteins / Q000737:chemistry*; D002237:Carbohydrate Dehydrogenases / Q000737:chemistry*; D002238:Carbohydrate Epimerases / Q000737:chemistry*; D002482:Cellulose / Q000737:chemistry; D019295:Computational Biology; D019848:Gene Expression Regulation, Archaeal; D005947:Glucose / Q000737:chemistry; D006031:Glycosylation; D019622:Haloferax volcanii / Q000201:enzymology*; D008562:Membrane Glycoproteins / Q000737:chemistry; D005810:Multigene Family; D009713:Nucleotidyltransferases / Q000737:chemistry*; D009844:Oligosaccharides / Q000737:chemistry; D010957:Plasmids; D011134:Polysaccharides / Q000737:chemistry; D012210:Rhamnose / Q000096:biosynthesis*; D001426:Bacterial Proteins
D019843:Archaeal Proteins; D002237:Carbohydrate Dehydrogenases; D002238:Carbohydrate Epimerases; D002482:Cellulose; D005947:Glucose; D008562:Membrane Glycoproteins; D009713:Nucleotidyltransferases; D009844:Oligosaccharides; D011134:Polysaccharides; D012210:Rhamnose; C107144:dTDP-4-dehydrorhamnose reductase; C020587:glucose-1-phosphate thymidylyltransferase; C020092:dTDP-4-ketorhamnose 3,5-epimerase; D001426:Bacterial Proteins