D. Dowbenko et al., CLONING OF A RAT HOMOLOG OF MOUSE GLYCAM-1 REVEALS CONSERVATION OF STRUCTURAL DOMAINS, The Journal of biological chemistry, 268(19), 1993, pp. 14399-14403
Recently we described the isolation of a mouse cDNA clone encoding a m
ucin-like endothelial glycoprotein that appears to function as an adhe
sive ligand for L selectin. This ligand has been named GlyCAM 1 (Gly-c
osylation-dependent Cell Adhesion Molecule 1) because its adhesive int
eractions with the L selectin lectin domain require that the GlyCAM 1
polypeptide chain be appropriately modified with carbohydrates. These
carbohydrate modifications include the addition of sialic acid as well
as sulfate residues to O-linked carbohydrate side chains that are clu
stered in two serine/threonine-rich domains of the mucin. An additiona
l interesting structure that may have relevance to the association of
GlyCAM 1 with the lumenal surface of the endothelium was a potential a
mphipathic helix at the C terminus of the glycoprotein. In order to ex
amine the importance of the postulated O-linked domains as well as the
potential amphipathic helix, we have cloned the rat homologue of GlyC
AM 1. The sequence of this clone reveals a serine/threonine-rich prote
in that is highly homologous with the mouse GlyCAM 1. As was found for
the mouse GlyCAM 1, the rat homologue shows a clustering of these pot
ential O-linked carbohydrate acceptors in two domains of the protein.
Interestingly, many of the serines and threonines are found to be spac
ed identically in the two homologues, consistent with the possibility
that both density and position of the O-linked side chains may be impo
rtant for appropriate L selectin-mediated adhesion. In support of its
postulated functional importance, the C-terminal potential amphipathic
helix is conserved in the rat homologue. Finally, immunoprecipitation
analysis of [S-35]sulfate-labeled rat lymph nodes with either a mouse
L selectin IgG chimera or a peptide antiserum directed against a rela
tively conserved portion of mouse GlyCAM 1 demonstrates a approximatel
y 45-kDa sulfated ligand in rat lymph nodes that is analogous to that
previously described for mouse lymph nodes.