J. Biol. Chem., Vol. 263, Issue 21, 10481-10488, 07, 1988
Structural heterogeneity of the noncollagenous domain of basement membrane collagen
JP Langeveld, J Wieslander, J Timoneda, P McKinney, RJ Butkowski, BJ Wisdom Jr and BG Hudson
Department of Biochemistry, University of Kansas Medical Center, Kansas City 66103.
The noncollagenous domain of collagen from three different basement
membranes of bovine origin (glomerular, lens capsule, and placental) was
excised with bacterial collagenase, purified under nondenaturing
conditions, and characterized. In each case the domain existed as a hexamer
comprised of four distinct subunits (alpha 1 (IV) NC1, alpha 2 (IV) NC1,
M2*, and M3). Each subunit exists in both monomeric and dimeric
(disulfide-cross-linked) forms. Certain dimers also exist which contain
nonreducible cross-links. The hexamers from the three membranes differ with
respect to stoichiometry of subunits and subunit isoforms and to the degree
of cross-linking of monomers into dimers. The minor subunits, M2* and M3,
vary in quantity over a 20-fold range relative to the major ones among the
three hexamers. The results indicate that: 1) at least two populations of
triple-helical collagen molecules, differing in chain composition, exist in
each membrane and that their relative proportions are tissue-specific; and
2) the chemical nature of the noncollagenous domain of these populations is
tissue-specific with regard to subunit isoforms and relative proportion of
reducible and nonreducible cross-links in dimers. A novel structural
feature of the noncollagenous domain of basement membrane collagen was also
evinced from these studies. Namely, that each of the four monomeric
subunits exists in charge isoforms.
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