Arch Virol (1997) 142: 2465±2481 Demonstration of peripheral fucose units in N-linked glycans of human immunode®ciency virus type 1 gp 120: effects on glycoprotein conformation A. Bolmstedt 1 , M. Biller 1 , J.-E. S. Hansen 2 , J. P. Moore 3 , and S. Olofsson 1 1 Department of Clinical Virology, University of Go Èteborg, Go Èteborg, Sweden 2 Department of Infectious Diseases, Hvidovre Hospital, Hvidovre, Denmark 3 Aaron Diamond AIDS Research Centre, New York University School of Medicine, New York, New York, U.S.A. Accepted July 17, 1997 Summary. Fucosylated N-linked glycans are important constituents of membrane glycoproteins, owing to their signi®cance as biologically active ligands for several selectins and their role in modulating protein conformation of viral glycoproteins. The human immunode®ciency virus type 1 (HIV-1) glycoprotein contains more than 30 different glycan structures but so far fucose was found associated solely with the innermost GlcNAc of N-linked glycans. In the present report we determined whether fucose units also were linked to the distal GlcNAc via a(1±3) or a(1±4) linkages in N-linked glycans of gp 120. [ 3 H]-fucose labelled gp 120 was subjected to endoglycosidase F digestion, releasing diantennary complex type N-linked glycans, but leaving the inner polypeptide-bound carbohydrates, GlcNAc and possibly associated fucose units, intact. Gel ®ltration of the digested material revealed that [ 3 H]-fucose label was released from gp 120 by this treatment, indicating presence of peripheral fucose units. Furthermore, [ 3 H]-focuse label was also released by treatment of the labelled gp 120 with an a-L-fucosidase speci®cally removing fucose in a(1±3) and a(1±4) linkages. Altogether the results indicated presence of fucose units linked to peripheral GlcNAc of gp 120 N-linked glycans. We have earlier shown that other peripheral carbohydrate determinants, i.e. b(1±4)- galactose on N-linked glycans, maintain a correct antigenic conformation of gp 120. Using a coupled ELISA system, where changes in antigenic behaviour of a viral glycoprotein were correlated to stepwise elimination of peripheral monosaccharides from N-linked glycans, we found that treatment of gp 120 with a pan-speci®c a-fucosidase as well as an enzyme speci®c for a(1±3)- or a(1± 4)-linked fucose disclosed a hidden linear epitope situated in the gp 120 C2 region. The effects of the general fucosidase on epitope exposure was more