Crystallization studies of cAMP-dependent protein kinase. Cocrystals of the catalytic subunit with a 20 amino acid residue peptide inhibitor and MgATP diffract to 3.0 A resolution.

Crystallographic studies of the catalytic subunit of cAMP-dependent protein kinase demonstrate that the presence of a 20 amino acid residue peptide inhibitor and MgATP during crystallization yields crystals with a different space group and, more significantly, makes an important difference in the quality of the resulting crystals. Under identical experimental conditions, the kinase crystallizes in a cubic space group P4(1)32 (a = b = c = 169.24 A), when no substrates or inhibitors are present, and in the hexagonal space group P6(1)22 (or P6(5)22) (a = b = 80.16 A, c = 288.07 A, alpha = beta = 90 degrees, gamma = 120 degrees) when a 20-amino acid residue peptide inhibitor and MgATP are present. Moreover, the hexagonal crystal diffracts to a resolution of 3.0 A, while the cubic crystals diffract to a resolution of 4.0 A.