Journal
JOURNAL OF STRUCTURAL BIOLOGY
Volume 131, Issue 1, Pages 44-55Publisher
ACADEMIC PRESS INC
DOI: 10.1006/jsbi.2000.4252
Keywords
atomic force microscopy (AFM); basal lamina; entropic brush; extracellular matrix (ECM); heparan sulfate proteoglycan (HSPG); laminin-1 (Ln-1); molecular volumes; type IV collagen (Col IV); scanning force microscope (SFM); scanning probe microscopy (SPM)
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The major macromolecules of basement membranes-collagen IV laminin-1, and heparan sulfate proteoglycan (HSPG)-have been analyzed by atomic force microscopy (AFM), both individually and in combination with each other. The positions of laminin binding to collagen TV were mapped and compared with the positions of imperfections in the amino acid sequence of collagen IV; the apparent molecular volumes of the HSPG proteoglycans were measured and used to estimate the corresponding molecular weights. Even the thin, thread-like strands of the polyanion heparan sulfate can be visualized with AFM without staining, coating, or fixation. These strands are single polysaccharide chains and are thus thinner than single-stranded DNA. The heparan sulfate strands in HSPG are necessary for protein filtration in kidney basement membranes. We propose that these thin strands filter proteins by functioning as an entropic brush-i.e., that they filter proteins by their constant thermally driven motion in the basement membrane. These AFM analyses in air are a step toward AFM analyses under fluid of basement membrane macromolecules interacting with each other. (C) 2000 Academic Press.
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