Alternative titles; symbolsSMALL SERINE/THREONINE PROTEIN KINASE; SSTKTSSK4HGNC Approved Gene Symbol: TSSK6Cytogenetic location: 19p13.11 Genomic coordinates...
Alternative titles; symbols
HGNC Approved Gene Symbol: TSSK6
Cytogenetic location: 19p13.11 Genomic coordinates (GRCh38): 19:19,514,218-19,515,547 (from NCBI)
TSSK6 is a serine/threonine protein kinase that is required for postmeiotic chromatin remodeling and male fertility (Spiridonov et al., 2005).
▼ Cloning and Expression
By searching databases using a protein kinase catalytic domain as query, Spiridonov et al. (2005) identified TSSK6, which they called SSTK. EST analysis suggested the existence of 3 TSSK6 splice variants that use 2 different polyadenylation sites. The deduced 273-amino acid TSSK6 protein has a calculated molecular mass of 30.3 kD and consists almost entirely of the N and C lobes of a protein kinase domain. TSSK6 possesses several essential protein kinase features, including a conserved active site, ATP-binding region, and potential activation loop phosphorylation motif. Northern blot analysis detected high expression of a 1.5-kb transcript in adult testis, with lower expression in colon, small intestine, ovary, prostate, thymus, spleen, and peripheral blood leukocytes. A 3-kb transcript was expressed in spinal cord and medulla oblongata. RT-PCR analysis confirmed that highest TSSK6 expression was in testis.
▼ Gene Function
Using wildtype TSSK6 and TSSK6 mutants expressed and immunopurified from 293T cells for in vitro protein kinase assays, Spiridonov et al. (2005) found that TSSK6 had protein kinase activity against myelin basic protein (MBP; 159430), as well as autophosphorylation activity. Lys41 and asp135 of TSSK6 were essential for MBP phosphorylation. TSSK6 phosphorylation of MBP occurred almost entirely on serines, and further studies using synthetic peptides showed that TSSK6 displayed highest phosphorylation activity on peptides containing a common RxxSxxR sequence. Coimmunoprecipitation analysis of TSSK6 expressed in 293T cells showed that TSSK6 bound heat-shock proteins HSP90-1-beta (HSPCB; 140572), HSC70 (HSPA8; 600816), and HSP70-1 (HSPA1A; 140550). In vitro phosphorylation studies showed that TSSK6 phosphorylated histones H1 (see 142711), H2A (see 613499), H2AX (H2AFX; 601772), and H3 (see 602810), but not H2B (see 602803), H4 (see 602822), or TP1 (TNP1; 190231).
By yeast 2-hybrid screening, Jha et al. (2010) identified human SIP (TSACC; 619679) as an SSTK-interacting protein. Immunohistochemical analysis of adult mouse testis showed that Sstk and Sip colocalized in the cytoplasm of elongated spermatids undergoing restructuring and chromosome condensation. In vitro analysis with purified recombinant proteins and coimmunoprecipitation analysis of transfected 293T cells confirmed direct interaction between SIP and SSTK. SIP inhibited SSTK catalytic activity in a dose-dependent manner in vitro, but it facilitated SSTK activation without affecting AKT (164730) or MAPK (see 176948) activity in transfected 293T cells, indicating that other proteins were involved in cellular activation of SSTK. Further analysis revealed that SIP interacted directly with HSP70 and recruited SIP to HSP90, thereby allowing SIP and HSP90 to work together in functional maturation of SSTK.
▼ Gene Structure
Spiridonov et al. (2005) determined that the TSSK6 gene contains 2 exons.
By genomic sequence analysis, Spiridonov et al. (2005) mapped the TSSK6 gene to chromosome 19. They mapped the mouse Tssk6 gene to chromosome 8. Hao et al. (2004) reported that the TSSK6 gene, which they called TSSK4, maps to chromosome 19p13.11, and that the mouse Tssk6 gene maps to chromosome 8B3.3.
▼ Animal Model
Spiridonov et al. (2005) found that Tssk6-null female mice were fertile, but Tssk6-null males were sterile and had reduced sperm counts, decreased sperm motility, and a dramatic increase in the percentage of sperm with abnormal morphology. Beginning at stage 10, Tssk6-null elongating spermatids displayed abnormal sperm head development characterized by increased space between the nuclear envelope and condensing nucleus of the posterior head. Stage-12 Tssk6-null elongating spermatids showed expansion of the perinuclear and subacrosomal space and accumulation of electron dense matter between the membranes of the head and nucleus. Spiridonov et al. (2005) concluded that Tssk6-null spermatozoa have impaired DNA condensation.