3.1.1 JAK and STAT structure
JAK kinases’ molecular weights are rigged 120-140kDa. They both contain seven conserved JH regions (JH1 ± JH7). They have four domains: FERM domain (a N-terminal four-point-one, ezrin, radixin, and meson; JH4~7), SH2 domain (JH3~4), a pseudo kinase domain (JH2), and a classical protein tyrosine kinase (PTK) domain (JH1)(Cai, Cai, Luo, Chen & Zhang, 2015). The JAK kinase mediated the signal transduction of almost 60 cytokines, hormones, and growth factors (GF)(O’Shea & Plenge, 2012).
The molecular weights of STAT proteins range from 79 to 113kDa, and they contain six domains: a N-terminal conserved domain, a DNA-binding domain, a SH3-like domain, a SH2 domains, and a C-terminal transcription domain. The N-terminal domain is vital for the STAT phosphorylation and the dimer-dimer interactions. The DNA binding domain usually locates between amino acids 400 and 500 and its function is to form a complex of DNA with the STAT protein. The SH2 domain has been reported contribute to the protein-protein interactions of STATs and other proteins. The C-terminal transcription domain is required for the activation of STATs with highly conserved phosphorylated tyrosine (Y) and serine (S) residues(Gao, Liang, Shaikh, Zang, Xu & Zhang, 2018). Besides transduction of JAK signals, the STATs are also found directly transcriptional inducted by STAT target genes.
FIGURE 1 JAK and STAT structure.