Bertenshaw Greg P, Villa James P, Hengst Jeremy A, Bond Judith S
Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey 17033, USA.
Biol Chem. 2002 Jul-Aug;383(7-8):1175-83. doi: 10.1515/BC.2002.129.
Meprin A and B are highly regulated, secreted and cell-surface homo- and hetero-oligomeric enzymes. Meprins are abundantly expressed in kidney and intestine. The multidomain alpha and beta subunits have high sequence identity, however they have very different substrate specificities, oligomerization potentials and are differentially regulated. Here we describe that meprin subunit activities are modulated differently by physico-chemical factors. Homo-oligomeric meprin B had an acidic pH optimum. The low pH protonation indicated the existence of at least two ionizable groups. An additional ionizable group generated a shoulder in the basic pH range. Homo-oligomeric meprin A had a neutral pH optimum and the activity curve revealed that two ionizable groups might be protonated at acidic pH similar to meprin B. Increasing the concentration of salt generally inhibited meprin B activity. Meprin A was inhibited at low salt concentrations but activated as salt was increased. This work has important implications in the elucidation of the catalytic mechanisms of meprins and other metalloproteases. In addition, the activity of meprin oligomers that arise in tissues will be affected by variations in pH and NaCl. This could have profound implications because meprins are exposed to a range of conditions in the extracellular milieu of renal and intestinal tissues and in inflammation and cancer.
梅普酶A和B是受到高度调控、可分泌的细胞表面同源和异源寡聚酶。梅普酶在肾脏和肠道中大量表达。多结构域的α和β亚基具有高度的序列同一性，然而它们具有非常不同的底物特异性、寡聚化潜能且受到不同的调控。在此我们描述了梅普酶亚基的活性受到物理化学因素的不同调节。同源寡聚的梅普酶B具有酸性的最适pH值。低pH值下的质子化表明存在至少两个可电离基团。在碱性pH范围内，一个额外的可电离基团产生了一个肩峰。同源寡聚的梅普酶A具有中性的最适pH值，并且活性曲线表明在酸性pH下可能有两个可电离基团与梅普酶B类似地发生质子化。增加盐浓度通常会抑制梅普酶B的活性。梅普酶A在低盐浓度下受到抑制，但随着盐浓度升高而被激活。这项工作对于阐明梅普酶和其他金属蛋白酶的催化机制具有重要意义。此外，组织中出现的梅普酶寡聚体的活性将受到pH值和氯化钠变化的影响。这可能具有深远的影响，因为梅普酶在肾脏和肠道组织的细胞外环境以及炎症和癌症中会暴露于一系列条件下。
