Phosphorylation of Sperm Axoneme Central Apparatus Protein SPAG16L by a Testis-specific Kinase, TSSK-2.

Abstract

Mammalian SPAG16L, the orthologue of Chlamydomonas Pf20, is an axoneme central apparatus protein necessary for flagellar motility. The SPAG16L protein sequence contains multiple potential phosphorylation sites and the protein was confirmed to be phosphorylated in vivo. A yeast-two-hybrid screen identified the testis-specific kinase, TSSK-2, to be a potential SPAG16L binding partner. SPAG16L and TSSK-2 interactions were confirmed by co-immunoprecipitation of both proteins from testis extracts and from cell lysates expressing these proteins, and their co-localization was also noted by confocal microscopy in CHO cells where they were co-expressed. TSSK-2 associates with SPAG16L via its C terminal domain bearing WD repeats. The N-terminal domain containing a coiled coil motif does not associate with TSSK-2. SPAG16L can be phosphorylated by TSSK-2 in vitro. Finally, TSSK-2 is absent from the testes in approximately half of SPAG16L null mice. These data support the conclusion that SPAG16L is a TSSK-2 substrate.