Agersnap Mikkel, Rehfeld Jens F
Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen , Denmark.
Scand J Clin Lab Invest. 2014 Aug;74(5):424-31. doi: 10.3109/00365513.2014.900695. Epub 2014 Apr 15.
Most proteins undergo posttranslational modifications that govern the function of the protein. In synchrony, correspondingly unmodified proteins that are functionally silent or act differently may also be synthesized. The gut hormone precursor, procholecystokinin (proCCK) is an example of a protein that is heavily modified. An essential modification is O-sulfation of Y₇₇, which is necessary for the gallbladder emptying effect of CCK peptides via the CCKA-receptor. In order to examine possible in vivo synthesis also of nonsulfated CCK, we have established a two-step analysis that requires tryptic cleavage at a defined processing site in proCCK (R₇₅-D₇₆) followed by monospecific RIA-measurement of the then exposed nonsulfated N-terminal sequence of CCK-8 (DYMGW…). The analysis shows that endocrine cells in the gut synthesize nonsulfated CCK peptides (-58, -33, -22, and -8) in the order of 20-35% of the corresponding sulfated CCKs. Since nonsulfated CCK peptides are full agonists of the CCKB-receptor, the assay has revealed a hitherto unrecognized gut hormonal peptide system. The assay may prove useful in the diagnosis and control of diseases with hyperCCKemia. This includes CCK-producing neuroendocrine tumors such as the recently described CCKomas and medullary thyroid C-cell carcinomas.
大多数蛋白质会经历影响其功能的翻译后修饰。与此同时，功能沉默或作用不同的相应未修饰蛋白质也可能被合成。肠道激素前体，即前胆囊收缩素（proCCK）就是一种经过大量修饰的蛋白质。一个关键修饰是Y₇₇的O-硫酸化，这对于胆囊收缩素肽通过CCKA受体产生胆囊排空作用是必需的。为了研究非硫酸化胆囊收缩素在体内的可能合成情况，我们建立了一种两步分析法，该方法需要在proCCK中一个确定的加工位点（R₇₅-D₇₆）进行胰蛋白酶切割，然后通过单特异性放射免疫分析测定随后暴露的非硫酸化胆囊收缩素-8（DYMGW…）的N端序列。分析表明，肠道内分泌细胞合成的非硫酸化胆囊收缩素肽（-58、-33、-22和-8）的量约为相应硫酸化胆囊收缩素肽的20 - 35%。由于非硫酸化胆囊收缩素肽是CCKB受体的完全激动剂，该检测方法揭示了一个迄今未被认识的肠道激素肽系统。该检测方法可能对高胆囊收缩素血症相关疾病的诊断和控制有用。这包括产生胆囊收缩素的神经内分泌肿瘤，如最近描述的胆囊收缩素瘤和甲状腺髓样C细胞癌。
