FIGURE 2.

Structural details of the SH2₁ and SH2₂ domains. A, ribbon representation of the SH2₁ domain. The arginine (R817) that is invariant in canonical SH2 domains is shown as sticks. The two residues (H838 and E804) forming a canonical hydrogen bond network with Arg⁸¹⁷ are also shown as well as other residues (S820 and K840) that might be involved in recognition of an incoming phosphoresidue. The surface of the SH2₁ domain is shown, highlighting the groove formed between the two SH2 domains that define the second binding pocket generally observed in canonical SH2 domains. B, ribbon representation of the SH2₂ domain. The tyrosine (Y906) that replaces the invariant arginine of canonical SH2 domains is shown as sticks as well as the glutamate (E926) forming a hydrogen bond with the hydroxyl of this tyrosine. The serine residue (S908) from the BC₂ loop that might be involved in recognition of an incoming phosphoresidue is also displayed. C, superposition of the SH2₁ (red) and SH2₂ (blue) domains, highlighting the difference of conformation between the two αA helices. For clarity, part of the N termini and the αB helices of the two domains has been removed.