Serine/threonine kinase which is involved in male germ cell development and in mature sperm function (By similarity). May be involved in the Cre/Creb signaling pathway (By similarity). Phosphorylates CREB1 on 'Ser-133' in vitro and can stimulate Cre/Creb pathway in cells (PubMed:15964553). Phosphorylates CREM on 'Ser-116' in vitro (By similarity). Phosphorylates ODF2 on 'Ser-95' (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phosphorylation on Thr-197. Homodimer (By similarity). Interacts with HSP90; this interaction stabilizes and activates TSSK4 (By similarity). Interacts with ODF2 (via C-terminus); this interaction promotes ODF2 phosphorylation on 'Ser-95' (By similarity). May interact with CREM (By similarity). Interacts with CREB1; this interaction facilitates phosphorylation on 'Ser-133' (PubMed:15964553). Interacts with QRICH2 (PubMed:30683861). In spermatozoa, present in the sperm head and in the flagellum. Expressed only in the testis. Activated by autophosphorylation on Thr-197. ODF2 potentiates the autophosphorylation activity of TSSK4 at Thr-197. Ubiquitinated; HSP90 activity negatively regulates ubiquitination and degradation. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family.