The rat
core-specific lectin (CSL) or
mannan-binding protein is synthesized and secreted by rat hepatocytes and H-4-II-E
hepatoma cells. Prior to secretion
proline and
lysine residues with
collagen-like sequences undergo hydroxylation and subsequent glycosylation of
hydroxylysine to produce
glucosylgalactosylhydroxylysine. Hydroxylation and subsequent glycosylation are inhibited by
alpha,alpha'-dipyridyl (Colley, K. J., and Baenziger, U. U. (1987) J. Biol. Chem. 262, 10290-10295). We have used
alpha,alpha'-dipyridyl to investigate the role of hydroxylation and glycosylation on interchain
disulfide bond formation, assembly of subunits into high molecular weight complexes, attainment of
carbohydrate and
lipid binding ability, and secretion. Formation of
disulfide-bonded dimers and trimers in the endoplasmic reticulum, assembly into high molecular weight complexes in the Golgi, and attainment of
carbohydrate binding activity occur in either the presence or absence of these post-translational modifications. The mature fully processed form of the CSL binds hydrophobic matrices and is secreted at a slow, but linear, rate. Inhibition of
proline and
lysine hydroxylation and
hydroxylysine glycosylation prevents CSL secretion and attainment of binding activity for hydrophobic matrices. Secretion of the
lectin, although slow, appears to be an active process and may be related to the capacity to interact with membranes and/or
lipids. Other
proteins known to contain
collagen-like sequences such as
acetylcholinesterase,
pulmonary surfactant apoproteins, and C1q also interact with
lipids and/or membranes. The
collagen-like domains of these
proteins may also play a role in promoting such interactions.