Mutations in the cathepsin K gene are associated with pycnodysostosis, a hereditary osteopetrotic disease, characterised by a lack of functional cathepsin K expression. Knockout studies of cathepsin K in mice lead to an osteopetrotic phenotype, which, is partially compensated by increased expression of proteases other that cathepsin K and enhanced osteoclastogenesis. Cathepsin K has an optimal enzymatic activity in acidic conditions. It is synthesized as a proenzyme with a molecular weight of 37kDa, and upon activation by autocatalytic cleavage, is transformed into the mature, active form with a molecular weight of ~27kDa. Upon polarization of the osteoclast over the site of resorption, cathepsin K is secreted from the ruffled border into the resorptive pit. Cathepsin K transmigrates across the ruffled border by intercellular vesicles and is then released by the functional secretory domain. Within these intercellular vesicles, cathepsin K, along with reactive oxygen species generated by TRAP, further degrades the bone extracellular matrix. Several other cathepsins are expressed in osteoclasts including cathepsins B, C, D, E, G, and L.  The function of these cysteine and aspartic proteases is generally unknown within bone, and they are expressed at much lower levels than cathepsin K.
Studies on cathepsin L knockout mice have been mixed, with a report of reduced trabecular bone in homozygous and heterozygous cathepsin L knockout mice compared to wild-type and another report finding no skeletal abnormalities. Matrix metalloproteinases
The matrix metalloproteinases (MMPs) comprise a family of more than 20 zinc-dependent endopeptidases.
After the addition of pathogenic antibodies against the acetylcholine receptor and activation of the complement system, the neuromuscular co-culture shows symptoms such as weaker muscle contractions. References
Further reading
Zhang Z, Guo J, Su G, Li J, Wu H, Xie X (17 November 2014). "Evaluation of the quality of guidelines for myasthenia gravis with the AGREE II instrument". PLOS ONE. 9 (11): e111796. Bibcode:2014PLoSO...9k1796Z. doi:10.1371/journal.pone.0111796. PMC 4234220. PMID 25402504. "NCBI – Diagnostic". www.ncbi.nlm.nih.gov. Retrieved 11 July 2015.