Abstract
PC2 and PC3, which is also known as PC1, are subtilisin-like proteases that are involved in the intracellular processing of prohormones and proneuropeptides. Both enzymes are synthesized as propolypeptides that undergo proteolytic maturation within the secretory pathway. An in vitro translation/translocation system from Xenopus egg extracts was used to investigate mechanisms in the maturation of pro-PC3 and pro-PC2. Pro-PC3 underwent rapid (t1/2 < 10 min) processing of the 88-kDa propolypeptide at the sequence RSKR83 to generate the 80-kDa active form of the enzyme. This processing was blocked when the active site aspartate was changed to asparagine, suggesting that an autocatalytic mechanism was involved. In this system, processing of pro-PC3 was optimal between pH 7.0 and 8.0 and was not dependent on additional calcium. These results are consistent with pro-PC3 maturation occurring at an early stage in the secretory pathway, possibly within the endoplasmic reticulum, where the pH would be close to neutral and the calcium concentration less than that observed in later compartments. Processing of pro-PC2 in the Xenopus egg extract was much slower than that of pro-PC3 (t1/2 = 8 h). It exhibited a pH optimum of 5.5-6.0 and was dependent on calcium (K0.5 = 2-4 mM). The enzymatic properties of pro-PC2 processing were similar to that of the mature enzyme. Further studies using mutant pro-PC2 constructs suggested that cleavage of pro-PC2 was catalyzed by the mature 68-kDa PC2 molecule. The results were consistent with pro-PC2 maturation occurring within a late compartment of the secretory pathway that contains a high calcium concentration and low pH.
Highlights
Undergo proteolytic maturation within the secretory pathway
PC2 is synthesized as a 69-kDa prepropolypeptide
The NH2terminal signal sequence is removed during segregation within the endoplasmic reticulum, where glycosylation generates a 75-kDa propolypeptide
Summary
Vol 270, No.[3], Issue of January 20, pp. 1402-1407, 1995 Printed in U.S.A. Differences in pH Optima and Calcium Requirements for Maturation of the Prohormone Convertases PC2 and PC3 Indicates Different Intracellular Locations for These Events*. PC2 and PC3, which is known as PC1, are subtilisin-like proteases that are involved in the intracellular processing of prohormones and proneuropeptides Both enzymes are synthesized as propolypeptides that undergo proteolytic maturation within the secretory pathway. ProPC3 underwent rapid (tIh < 10 min) processing of the 88-kDa propolypeptide at the sequence RSKR83 to generate the 80-kDa active form of the enzyme This processing was blocked when the active site aspartate was changed to asparagine, suggesting that an autocatalytic mechanism was involved. Expression ofPC2 and PC3 is restricted to neuroendocrine cells, which is compatible with their role in the processing of proneuropeptides and prohormones Both enzymes require pairs of basic amino acids at their cleavage site. PC3 is synthesized as an 88-kDa propolypeptide that undergoes cleavage at the sequence RSKR83 to generate an 80-kDa active form of the enzyme (Benjannet et al, 1992; Zhou and Lindberg, 1993). The results suggest that pro-PC3 may undergo autocatalytic processing within the endoplasmic reticulum or early secretory compartment where the pH is near neutral and the calcium concentration in the micromolar range, while pro-PC2 processing occurs in a late secretory compartment where the pH is low (5.5) and the calcium concentration within the millimolar range
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
