Chronic Disease Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada.
Mol Cell Biochem. 2011 Feb;348(1-2):43-52. doi: 10.1007/s11010-010-0635-y. Epub 2010 Nov 16.
Proprotein convertase subtilisin/kexin type 4 (PCSK4), also known as proprotein convertase 4 (PC4), is a serine endoproteinase primarily expressed in testicular germ cells and in sperm. Inactivation of its gene in mouse causes male infertility. From studies of the biosynthesis of PCSK3/furin, its closest relative, it has been inferred that PCSK4 is synthesised in the endoplasmic reticulum as a zymogen; that it is rapidly matured by autocatalytic cleavage between the prodomain and the catalytic domain; that the cleaved prodomain remains attached to the mature enzyme; and that the enzyme is finally activated by the removal of the prodomain peptides following a secondary cleavage within the prodomain. In this study, we used human embryonic kidney 293 (HEK293) cells to study the biosynthesis of rat or human PCSK4. Our results show that the bulk of PCSK4 remains as an intracellular zymogen, presumably trapped in the endoplasmic reticulum, where it interacts with the general molecular chaperone glucose-regulated protein 78/Immunoglobulin heavy-chain binding protein (GRP78/BiP). These data suggest that, unlike other members of the convertase family, proPCSK4 cannot efficiently self-activate in somatic cells. These cells may lack the intracellular environment and the interacting molecules specific to testicular germ cells where this enzyme is normally expressed.
脯氨酸羧肽酶/丝氨酸内肽酶 4（PCSK4），也称为脯氨酸羧肽酶 4（PC4），是一种主要在睾丸生殖细胞和精子中表达的丝氨酸内肽酶。其基因在小鼠中的失活导致雄性不育。从对 PCSK3/弗林蛋白酶（其最接近的亲属）生物合成的研究中推断，PCSK4 在粗面内质网中作为酶原合成；它通过在原结构域和催化结构域之间的自动催化裂解迅速成熟；裂解的原结构域仍然附着在成熟酶上；并且该酶最终通过在原结构域内的二次裂解除去原结构域肽而被激活。在这项研究中，我们使用人胚肾 293（HEK293）细胞来研究大鼠或人 PCSK4 的生物合成。我们的结果表明，大部分 PCSK4 仍然作为细胞内酶原存在，可能被困在内质网中，在那里它与一般分子伴侣葡萄糖调节蛋白 78/免疫球蛋白重链结合蛋白（GRP78/BiP）相互作用。这些数据表明，与转化酶家族的其他成员不同，原 PCSK4 不能在体细胞中有效地自我激活。这些细胞可能缺乏该酶通常表达的睾丸生殖细胞特有的细胞内环境和相互作用分子。
