Basement membranes domains

Type XV and XVIII collagens are classified as basement membrane zone collagens or multiplexins (multiple triple helix domains and interruptions) by Olsen and coworkers. From a biological aspect, basement... 

Type XXVIII collagen belongs to the class of VWA domain-containing proteins. The primary structure is similar to type VI collagen. It is mainly a component of the basement membranes around Schwann cells in the peripheral nervous system. ... 

Siebold, B., Deutzmann, R., and Khun, K. (1988). The arrangement of inter- and intramolecular disulphide bonds in the carboxyterminal, non-collagenous aggregations and cross-linking domain of basement membrane Type IV collagen. Eur. J. Biochem. 176, 617-624. 

Sundaramoorthy, M., Meiyappan, M., Todd, P., and Hudson, B. G. (2002). Crystal structure of NCI domains Structural basis for type IV collagen assembly in basement membranes. /. Biol. Chem. 277, 31142-31153. 

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. 

Podocytes are polarized cells, so one can differentiate between luminal and abluminal (basal) membrane domains (the basal domain corresponds to the sole plates of the foot processes, which are embedded in the basement membrane). The slit diaphragm forms the border between the luminal and the abluminal membranes. 

A better understanding of the structure of collagen IV molecules explains some previous observations. The occurrence of the 7 S domain and nonhelical interruptions in the molecule can explain in part the heterogeneous mixture of collagenous components isolated from basement membrane, particularly when pepsin or other proteases are used to solubilize the protein. The molecules isolated from lathyritic basement membrane by acid extraction are truncated and lack the 7 S domain presumably due to cleavage by endogenous proteases. 

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