FSCB phosphorylation in mouse spermatozoa capacitation.

It is generally accepted that spermatozoa capacitation is associated with protein kinase A-mediated tyrosine phosphorylation. In our previous study, we identified the fibrous sheath CABYR binding protein (FSCB), which was phosphorylated by PKA. However, the phosphorylation status of FSCB protein during spermatozoa capacitation should be further investigated. To this aim, in this study, we found that phosphorylation of this 270-kDa protein occurred as early as 1 min after mouse spermatozoa capacitation, which increased over time and remained stable after 60 min. Immunoprecipitation assays demonstrated that the tyrosine and Ser/Thr phosphorylation of FSCB occurred during spermatozoa capacitation. The extent of phosphorylation and was closely associated with the PKA activity and spermatozoa motility characteristics. FSCB phosphorylation could be induced by PKA agonist DB-cAMP, but was blocked by PKA antagonist H-89.Therefore, FSCB contributes to spermatozoa capacitation in a tyrosine-phosphorylated format, which may help in further elucidating the molecular mechanism of spermatozoa capacitation.