STRUCTURE OF THE MAMMALIAN CATALYTIC SUBUNIT OF CAMP-DEPENDENT PROTEIN-KINASE AND AN INHIBITOR PEPTIDE DISPLAYS AN OPEN CONFORMATION

The crystal structure of a binary complex of the porcine heart catalytic (C) subunit of cAMP-dependent protein kinase (space group P4(1)32; a = 171.5 angstrom) complexed with a di-iodinated peptide inhibitor, PKI(5-24), has been solved and refined to 2.9 angstrom resolution with an overall R of 21.1%. The r.m.s. deviations from ideal bond lengths and angles are 0.022 angstrom and 4.3-degrees. A single isotropic B of 17 angstrom2 was used for all atoms. The structure solution was carried out initially by molecular replacement of electron density followed by refinement against atomic coordinates from orthorhombic crystals of a binary complex of the mouse recombinant enzyme previously described [Knighton, Zheng, Ten Eyck, Ashford, Xuong, Taylor & Sowadski (1991). Science, 253, 407-414]. The most striking difference between the two crystal structures is a large displacement of the small lobe of the enzyme. In the cubic crystal, the beta-sheet of the small lobe is rotated by 15-degrees and translated by 1.9 angstrom with respect to the orthorhombic crystal. Possible explanations for why this binary complex crystallized in an open conformation in contrast to a similar binary complex of the recombinant enzyme are discussed. This study demonstrates that considerable information about parts of a crystal structure can be obtained without a complete crystal structure analysis. Specifically, the six rigid-group parameters of a poly-alanine model of the beta-structure were obtained satisfactorily from a crystal structure by refinement of difference Fourier coefficients based on an approximate partial structure model.