Oligosaccharyl transferase (OST) that catalyzes the initial transfer of a defined glycan (a GalNAc-linked heptasaccharide composed of 4 Hex, 3 dHex and a sulfate for A.fulgidus AglB-S) from the lipid carrier dolichol-monophosphate to an asparagine residue within an Asn-X-Ser/Thr consensus motif in nascent polypeptide chains, the first step in protein N-glycosylation. an archaeal dolichyl phosphooligosaccharide + [protein]-L-asparagine = an archaeal dolichyl phosphate + a glycoprotein with the oligosaccharide chain attached by N-beta-D-glycosyl linkage to a protein L-asparagine. Protein modification; protein glycosylation. Belongs to the STT3 family.