Identification of a cysteine protease responsible for degradation of sperm histones during male pronucleus remodeling in sea urchins

✍ Scribed by Maria Imschenetzky; Fredy Díaz; Martin Montecino; Felipe Sierra; Marcia Puchi

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 379 KB
• Volume: 67
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/(sici)1097-4644(19971201)67:3<304::aid-jcb3>3.0.co;2-#

✦ Synopsis

We have identified a 60-kDa cysteine protease that is associated with chromatin in sea urchin zygotes. This enzyme was found to be present as a proenzyme in unfertilized eggs and was activated shortly after fertilization. At a pH of 7.8-8.0, found after fertilization, the enzyme degraded the five sperm-specific histones (SpH), while the native cleavage-stage (CS) histone variants remained unaffected. Based on its requirements for reducing agents, its inhibition by sulfhydryl blocking compounds and its sensitivity to the cysteine-type protease inhibitors (2S,3S)-trans-epoxysuccinyl-L-leucyl-amido-3-methylbutane-ethyl-es ter (E-64 d), cystatin and leupeptin, this protease can be defined as a cysteine protease. Consistently, this protease was not affected by serine-type protease inhibitors phenylmethylsulfonyl fluoride (PMSF) and pepstatin. The substrate selectivity and pH modulation of the protease activity strongly suggest its role in the removal of sperm-specific histones, which determines sperm chromatin remodeling after fertilization. This suggestion was further substantiated by the inhibition of sperm histones degradation in vivo by E-64 d. Based on these three lines of evidence, we postulate that this cysteine protease is responsible for the degradation of sperm-specific histones which occurs during male pronucleus formation.