Figure 2.

Hydrophobic residues on the surface of the RA2 domain are critical for activation.A, the structure of H-Ras (gray) bound to the RA2 domain (blue, PDB entry 2C5L (14)) reveals conserved, hydrophobic residues (teal spheres) involved in crystal lattice contacts. Lys²¹⁷¹ and Lys²¹⁷³ (hot pink spheres) were previously reported to be required for Rap1A-dependent activation. R. norvegicus residues are in parentheses. GTP is shown as orange sticks, and Mg²⁺ is shown as a black sphere. B and C, mutation of the Lys²¹⁵⁰ or Lys²¹⁵² to alanine eliminates activation by Rap1A^G12Vin vitro (B), as does mutation of the conserved hydrophobic residues distant from the Rap1A binding surface (C).