P14317

HS1 also known as p75, LckBP1, HCLS1 is a protein kinase substrate that is expressed only in tissues and cells of hematopoietic origin. HS1 plays a crucial role in T cell activation by associating directly with the Src homology 3 (SH3) domain of the Lck tyrosine kinase, which is essential for T cell receptor (TCR) signaling. This interaction is facilitated by two proline-rich regions within HS1, highlighting its importance in the modulation of T cell responses. Additionally, HS1 contains four tandem 37 amino acid repeats that form a putative helix-loop-helix DNA binding motif, suggesting a potential role in gene regulation following T cell activation. Notably, HS1 is tyrosine phosphorylated in T cells after TCR engagement, indicating its involvement in downstream signaling pathways that are critical for T cell proliferation and differentiation.