Blanco Elias H, Peinado Juan R, Martín Martín G, Lindberg Iris
Department of Anatomy and Neurobiology (E.H.B., J.R.P., I.L.), University of Maryland Medical School, Baltimore, Maryland 21201; and Department of Pediatrics (M.G.M.), Division of Gastroenterology and Nutrition, Mattel Children's Hospital and the David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095.
Endocrinology. 2014 Sep;155(9):3434-47. doi: 10.1210/en.2013-2151. Epub 2014 Jun 16.
Satiety and appetite signaling are accomplished by circulating peptide hormones. These peptide hormones require processing from larger precursors to become bioactive, often by the proprotein convertase 1/3 (PC1/3). Several subcellular maturation steps are necessary for PC1/3 to achieve its optimal enzymatic activity. Certain PC1/3 variants found in the general population slightly attenuate its enzymatic activity and are associated with obesity and diabetes. However, mutations that increase PC1/3 activity and/or affect its specificity could also have physiological consequences. We here present data showing that the known human Ser357Gly PC1/3 mutant (PC1/3(S357G)) represents a PC1/3 hypermorph. Conditioned media from human embryonic kidney-293 cells transfected with PC1/3(WT) and PC1/3(S357G) were collected and enzymatic activity characterized. PC1/3(S357G) exhibited a lower calcium dependence; a higher pH optimum (neutral); and a higher resistance to peptide inhibitors than the wild-type enzyme. PC1/3(S357G) exhibited increased cleavage to the C-terminally truncated form, and kinetic parameters of the full-length and truncated mutant enzymes were also altered. Lastly, the S357G mutation broadened the specificity of the enzyme; we detected PC2-like specificity on the substrate proCART, the precursor of the cocaine- and amphetamine regulated transcript neuropeptide known to be associated with obesity. The production of another anorexigenic peptide normally synthesized only by PC2, αMSH, was increased when proopiomelanocortin was coexpressed with PC1/3(S357G). Considering the aberrant enzymatic profile of PC1/3(S357G), we hypothesize that this enzyme possesses unusual processing activity that may significantly change the profile of circulating peptide hormones.
饱腹感和食欲信号传导是通过循环肽激素来实现的。这些肽激素通常需要从前体蛋白加工成生物活性形式，这一过程往往由前蛋白转化酶1/3（PC1/3）完成。PC1/3要达到最佳酶活性需要几个亚细胞成熟步骤。在普通人群中发现的某些PC1/3变体可略微减弱其酶活性，并与肥胖症和糖尿病相关。然而，增加PC1/3活性和/或影响其特异性的突变也可能产生生理后果。我们在此展示的数据表明，已知的人类Ser357Gly PC1/3突变体（PC1/3(S357G)）代表一种PC1/3超形态。收集用PC1/3(WT)和PC1/3(S357G)转染的人胚肾293细胞的条件培养基，并对酶活性进行表征。与野生型酶相比，PC1/3(S357G)表现出较低的钙依赖性、更高的最适pH值（中性）以及对肽抑制剂更高的抗性。PC1/3(S357G)对C末端截短形式的切割增加，全长和截短突变体酶的动力学参数也发生了改变。最后，S357G突变拓宽了该酶的特异性；我们在底物proCART上检测到了PC2样特异性，proCART是已知与肥胖症相关的可卡因和苯丙胺调节转录物神经肽的前体。当阿黑皮素原与PC1/3(S357G)共表达时，另一种通常仅由PC2合成的厌食肽αMSH的产生增加。考虑到PC1/3(S357G)异常的酶谱，我们推测这种酶具有不寻常的加工活性，可能会显著改变循环肽激素的谱。
