P. Mishra, Q. Qiu, A. Gruslin, Y. Hidaka, M. Mbikay and A. Basak Pages 1050 - 1067 ( 18 )
PC4 or PCSK4 belongs to the 9-member superfamily of mammalian subtilases collectively called Proprotein Convertases or Proprotein Convertase Subtilisin/Kexins that convert inactive precursor proteins into their active mature forms by endoproteolytic cleavage. PC4-activity plays a crucial role in mammalian fertilization via activation of sperm surface proteins. PC4 knockout mice exhibit severely impaired male fertility due to premature sperm acrosome reaction. Regulation of sperm-PC4 activity during its storage and transport through epididymis is an important determinant for ultimate egg-binding and fertilizing capacities of sperms. Herein we show that epididymal serpin CRES (cystatin related epididymal spermatogenic) recombinant protein inhibits PC4 activity in vitro in a differential manner when measured against the fluorogenic substrate Boc- RVRR-MCA depending on its oligomeric state. Thus while CRES-dimer exhibits Ki ~8 μM, the corresponding monomer showed Ki > 100 μM. Both forms also blocked PC4-mediated processing of human proIGF-2 in human placenta tropoblast cell line with dimer being more efficient. Using specific inhibitors and substrates, we also demonstrated the presence of PC4-like activity and CRES protein in varying levels in the fluids of various epididymal compartments. Our observations suggest a potential function of CRES as a regulator of PC4 in sperm-egg interaction and fertilization.
Proprotein convertase 4, proprotein convertase subtilisin kexin 4, serpin, epididymal fluid, cystatin related epididymal spermatogenic, inhibitor, protein aggregation, proprotein processing, yeast kexin, bacterial subtilisin, proneuropeptides, prohormones, maturation, autocatalysis, fertilization.
Chronic Disease Program, Regional Protein Chemistry Center, Ottawa Hospital Research Institute, 725 Parkdale Ave, Ottawa, ON K1Y 4E9, Canada.