Rockwell Nathan C, Fuller Robert S
Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA.
J Biol Chem. 2002 May 17;277(20):17531-7. doi: 10.1074/jbc.M111909200. Epub 2002 Mar 13.
Kex2 protease is the prototype for a family of proteases responsible for endoproteolytic cleavage at multi-basic motifs in the eukaryotic secretory pathway. Here we demonstrate that potassium ion can act as a modulator of Kex2 activity with an apparent affinity of approximately 20 mm. Other monovalent cations (Li(+), Na(+), etc.) display similar effects, but affinities are all over 20-fold lower. Potassium ion binding stimulates turnover at physiologically relevant Lys-Arg cleavage sites but reduces turnover with at least one incorrect sequence. Furthermore, the mammalian Kex2 homolog furin displays similar effects. In contrast, the neuroendocrine homolog PC2 is inhibited by potassium ion with all substrates examined. The pre-steady-state behavior of Kex2 is also altered upon binding of potassium ion, with opposite effects on acylation and deacylation rates. These biochemical data indicate that potassium ion concentration may function as a regulator of processing protease specificity and activity in the eukaryotic secretory pathway, with such enzymes potentially encountering compartments high in potassium ion caused by the action of antiporters such as yeast NHX1 (VPS44) or the mammalian NHE7.
Kex2蛋白酶是一类蛋白酶的原型，这类蛋白酶负责真核生物分泌途径中多碱性基序处的内切蛋白水解切割。在此我们证明，钾离子可作为Kex2活性的调节剂，其表观亲和力约为20 mM。其他单价阳离子（Li⁺、Na⁺等）表现出类似效应，但亲和力均低20倍以上。钾离子结合可刺激生理相关的Lys-Arg切割位点的周转，但会降低至少一个错误序列的周转。此外，哺乳动物Kex2同源物弗林蛋白酶也表现出类似效应。相比之下，神经内分泌同源物PC2在所有检测的底物上均受到钾离子抑制。钾离子结合后，Kex2的稳态前行为也会改变，对酰化和去酰化速率产生相反影响。这些生化数据表明，钾离子浓度可能作为真核生物分泌途径中加工蛋白酶特异性和活性的调节剂，这类酶可能会遇到由酵母NHX1（VPS44）或哺乳动物NHE7等反向转运蛋白作用导致钾离子浓度较高的区室。
