Cathepsin membrane binding

Vitamin B12. Vitamin B12 is a larger molecule than the other vitamins, and it can be absorbed via the intestine, which involves binding to specialized transport proteins.44 After oral administration, vitamin B12 binds to intrinsic factor (IF) produced from the parietal cells in the stomach and proximal cells in the duodenum. The vitamin B12—IF complex passes down the small intestine until it reaches the ileum, where the complex binds to a specific IF receptor located on the apical membrane of the villous enterocyte. The complex is then internalized via RME, vitamin B12 is released from IF by the action of cathepsin L on IF, and free vitamin B12 consequently forms the complex with transcobal-amin II to be delivered into the basolateral side of the membrane via the transcytotic pathway. 

When the ODF/ODAR complex activates c-src to form a ruffled membrane, it also activates NFkB to activate the transcription factors that induce cathepsin K and acid phosphatase expression. Because ODF binds to ODAR/RANK, it is also known as the RANK ligand (RANKL). OCIF (OPG), the ODF decoy receptor, is RANK without its transmembrane and cytosolic domains. Thus OCIF = OPG and OPG ligand (OPGL) = RANKL = ODF. ODF, ODAR, and OCIF are related to TNFa or its receptor, TNFa family molecules (Table 10.1). 

E.J. Campbell, C.A. Owen, The sulfate groups of chondroitin sulfate- and heparan sulfate-containing proteoglycans in neutrophil plasma membranes are novel binding sites for human leukocyte elastase and cathepsin G, J. Biol. Chem. 282 (19) (2007) 14645-14654. 

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