Basement membrane binding

Bergey, E. J., and Stinson, M. W. (1988). Heparin-inhibitable basement membrane-binding protein of Streptococcus pyogenes. Infect. Immun. 56,1715-1721. 

Speziale, P., Hook, M., Wadstrom, T., and Timpl, R. (1982). Binding of basement membrane protein laminin to Escherichia coli. FEBS Lett. 175, 55-58. 

The structure of PTPo is consistent with its role in binding ligands on the surface of other cells or in the extracellular matrix. It interacts with heparin sulphate proteoglycan in the basement membrane (Sajnani-Perez et al. 2003). It may also bind to the C-terminal domain of cell surface-exposed nucleolin, a normally nuclear protein that is presented on the surface of developing muscle cells (Alete et al. 2006). However, these complexes seem to mediate structural or long-term regulatory interactions rather than short-term signaling to the neuronal secretory machinery. 

There are many other reports arguing against this mechanism as the major pathogenetic pathway of lupus nephritis. The presence of circulating DNA/anti-DNA immune complexes is difficult to detect (B25,13). Moreover, recent studies demonstrated that the levels of circulating DNA (nucleosome) immune complexes were low (B28, F8, L14). Data also suggest that DNA/anti-DNA complexes are rapidly cleared by the liver (E5) and bind poorly to glomerular basement membrane (GBM) (12). 

Collagen IV has been found to bind to both laminin and heparan sulfate proteoglycan, whereas laminin binds both the nidogen and heparan sulfate proteoglycan. These observations suggest that multiple interactions of a specific nature could be important in determining both the composition and the deposition of basement membranes. 

In summary, both collagen IV and laminin show the ability to self-assemble. In addition, the various components of basement membrane have an affinity for one another that involves binding to specific sites. These interactions generate rather defined aggregates in solution and lead to the deposition of the components in a gel-like form whose ultrastructure resembles in some details authentic basement membranes. Such multiple interactions would be expected to be stronger than single interactions and may account for the codistributions of these components in basement membranes. 

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