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Department of Cell Biology, and Cell Adhesion and Matrix Research Center, University of Alabama at Birmingham 35294-0019
Basement membranes contain several proteoglycans, and those bearing heparan sulfate glycosaminoglycans such as perlecan and agrin usually
predominate. Most mammalian basement membranes
also contain chondroitin sulfate, and a core protein,
bamacan, has been partially characterized. We have
now obtained cDNA clones encoding the entire bamacan core protein of Mr = 138 kD, which reveal a five
domain, head-rod-tail configuration. The head and tail
are potentially globular, while the central large rod
probably forms coiled-coil structures, with one large
central and several very short interruptions. This molecular architecture is novel for an extracellular matrix
molecule, but it resembles that of a group of intracellular proteins, including some proposed to stabilize the
mitotic chromosome scaffold. We have previously proposed a similar stabilizing role for bamacan in the basement membrane matrix. The protein sequence has low
overall homology, apart from very small NH2- and
COOH-terminal motifs.
At the junctions between the distal globular domains
and the coiled-coil regions lie glycosylation sites, with
up to three N-linked oligosaccharides and probably
three chondroitin chains. Three other Ser-Gly dipeptides are unfavorable for substitution. Fusion protein
antibodies stained basement membranes in a pattern commensurate with bamacan, and they also Western
blotted bamacan core protein from rat L2 cell cultures.
The antibodies could also specifically immunoprecipitate an in vitro transcription/translation product from a
full-length bamacan cDNA. The unusual structure of
this proteoglycan is indicative of specific functional
roles in basement membrane physiology, commensurate with its distinct expression in development and
changes in disease models.
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