The proteolytic maturation of prohormone convertase 2 (PC2) is a pH-driven process

被引:39
作者
Lamango, NS [1 ]
Apletalina, E [1 ]
Liu, J [1 ]
Lindberg, I [1 ]
机构
[1] Louisiana State Univ, Med Ctr, Dept Biochem & Mol Biol, New Orleans, LA 70112 USA
关键词
D O I
10.1006/abbi.1998.1033
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Recombinant proPC2 purified from the medium of CHO cells overexpressing both the prohormone convertase (PC) precursor proPC2 and the 21-kDa amino terminal portion of the neuroendocrine protein 7B2 can spontaneously convert to an active species. In the present report, we have characterized the proPC2 zymogen conversion process. Sequencing of the mature 66 kDa enzyme revealed a single site of cleavage at the paired basic site amino terminal to the GYRDI sequence. In contrast to mature PC2 activity, proPC2 conversion was inhibited neither by the eukaryotic subtilisin inhibitor pCMS nor by the specific PC2 inhibitor, 7B2 CT peptide, suggesting significant differences between the proPC2 conversion reaction and the hydrolysis of synthetic substrates by mature PC2, In support of this idea, proPC2 conversion was not calcium dependent and was unaffected by 5 mM EDTA. The rate of conversion of proPC2 remained similar with a 10-fold difference in zymogen concentration, implicating an intramolecular rather than intermolecular mechanism of activation Interestingly, the rate of proPC2 conversion was extremely pH dependent, occurring most extensively between pHs 4.0 and 4.9. Taken together, our results suggest that cellular proPC2 maturation occurs via an autocatalytic, intramolecular process controlled not by 7B2 inhibition nor by calcium levels, but by the decreasing pH gradient along the secretory pathway. (C) 1999 Academic Press.
引用
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页码:275 / 282
页数:8
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