The SH2 domain of SH2B1 binds phosphotyrosine-813 of JAK2 (Nishi et al. 2005, Li et al. 2007). Binding of SH2B1 to JAK2 enhances leptin-induced JAK2 activity. SH2B1 also recruits IRS1 for phosphorylation by JAK2 (Li et al. 2007).