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M28 Zn-peptidase glutaminyl cyclase Peptidase M28 family, glutaminyl cyclase (QC; EC 2.3.2.5) subfamily. QC is involved in N-terminal glutamine cyclization of many endocrine peptides and is typically abundant in brain tissue. N-terminal glutamine residue cyclization is an important post-translational event in the processing of numerous bioactive proteins, including neuropeptides, hormones, and cytokines during their maturation in the secretory pathway. The N-terminal pGlu protects them from exopeptidase degradation and/or enables them to have proper conformation for binding to their receptors. QCs are highly conserved from yeast to human. In humans, several genetic diseases, such as osteoporosis, appear to result from mutations of the QC gene. N-terminal glutamate cyclization into pyroglutamate (pGlu) is a reaction that may be related to the formation of several plaque-forming peptides, such as amyloid-(A) peptides and collagen-like Alzheimer amyloid plaque component, which play a pivotal role in Alzheimer's disease. |
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