Structural analysis of protein kinase A mutants with Rho-kinase inhibitor specificity.

Controlling aberrant kinase-mediated cellular signaling is a major strategy in cancer therapy; successful protein kinase inhibitors such as Tarceva and Gleevec verify this approach. Specificity of inhibitors for the targeted kinase(s), however, is a crucial factor for therapeutic success. Based on homology modeling, we previously identified four amino acids in the active site of Rho-kinase that likely determine inhibitor specificities observed for Rho-kinase relative to protein kinase A (PKA) (in PKA numbering: T183A, L49I, V123M, and E127D), and a fifth (Q181K) that played a surprising role in PKA-PKB hybrid proteins.

Crystallography for protein kinase drug design: PKA and SRC case studies.

Protein crystallography can be used throughout the drug discovery process to obtain diverse information critical for structure based drug design. At a minimum, a single target structure may be available. Optimally, and especially for protein kinases, a broad range of crystal structures should be obtained to characterize target flexibility, structure modulation via co-factor binding or posttranslational modification, ligand induced conformational changes, and off-target complex structures for selectivity optimization.

Crystal structures of active SRC kinase domain complexes.

c-Src was the first proto-oncoprotein to be identified, and has become the focus of many drug discovery programs. Src structures of a major inactive form have shown how the protein kinase is rigidified by several interdomain interactions; active configurations of Src are generated by release from this "assembled" or "bundled" form. Despite the importance of Src as a drug target, there is relatively little structural information available regarding the presumably more flexible active forms.

Design and crystal structures of protein kinase B-selective inhibitors in complex with protein kinase A and mutants.

Protein kinase B (PKB)-selective inhibitors were designed, synthesized, and cocrystallized using the AGC kinase family protein kinase A (PKA, often called cAMP-dependent protein kinase); PKA has been used as a surrogate for other members of this family and indeed for protein kinases in general. The high homology between PKA and PKB includes very similar ATP binding sites and hence similar binding pockets for inhibitors, with only few amino acids that differ between the two kinases. A series of these sites were mutated in PKA in order to improve the surrogate model for a design of PKB-selective inhibitors.

Structural insights into AGC kinase inhibition.

The AGC group of protein kinases comprises several targets for small molecule inhibitors of therapeutic significance. Crystal structure data facilitate the design or improvement of selective inhibitory molecules. Cross-selectivity of kinase inhibitors is often observed among closely related enzymes.

The typically disordered N-terminus of PKA can fold as a helix and project the myristoylation site into solution.

Protein kinases comprise the major enzyme family critically involved in signal transduction pathways; posttranslational modifications affect their regulation and determine signaling states. The prototype protein kinase A (PKA) possesses an N-terminal alpha-helix (Helix A) that is atypical for kinases and is thus a major distinguishing feature of PKA. Its physiological function may involve myristoylation at the N-terminus and modulation via phosphorylation at serine 10.

Structure-based optimization of novel azepane derivatives as PKB inhibitors.

Novel azepane derivatives were prepared and evaluated for protein kinase B (PKB-alpha) and protein kinase A (PKA) inhibition. The original (-)-balanol-derived lead structure (4R)-4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzoic acid (3R)-3-[(pyridine-4-carbonyl)amino]-azepan-4-yl ester (1) (IC(50) (PKB-alpha) = 5 nM) which contains an ester moiety was found to be plasma unstable and therefore unsuitable as a drug. Based upon molecular modeling studies using the crystal structure of the complex between PKA and 1, the five compounds N-[(3R,4R)-4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzoylamino]-azepan-3-yl]-isonicotinamide (4), (3R,4R)-N-[4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzyloxy]-azepan-3-yl]-isonicotinamide (5), N-[(3R,4S)-4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-phenylamino]-methyl]-azepan-3-yl)-isonicotinamide (6), N-[(3R,4R)-4-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-benzylamino]-azepan-3-yl]-isonicotinamide (7), and N-[(3R,4S)-4-(4-[trans-2-[4-(2-fluoro-6-hydroxy-3-methoxy-benzoyl)-phenyl]-vinyl]-azepan-3-yl)-isonicotinamide (8) with linkers isosteric to the ester were designed, synthesized, and tested for in vitro inhibitory activity against PKA and PKB-alpha and for plasma stability in mouse plasma.

The protein kinase C inhibitor bisindolyl maleimide 2 binds with reversed orientations to different conformations of protein kinase A.

As the key mediators of eukaryotic signal transduction, the protein kinases often cause disease, and in particular cancer, when disregulated. Appropriately selective protein kinase inhibitors are sought after as research tools and as therapeutic drugs; several have already proven valuable in clinical use. The AGC subfamily protein kinase C (PKC) was identified early as a cause of cancer, leading to the discovery of a variety of PKC inhibitors.

Protein kinase A in complex with Rho-kinase inhibitors Y-27632, Fasudil, and H-1152P: structural basis of selectivity.

Protein kinases require strict inactivation to prevent spurious cellular signaling; overactivity can cause cancer or other diseases and necessitates selective inhibition for therapy. Rho-kinase is involved in such processes as tumor invasion, cell adhesion, smooth muscle contraction, and formation of focal adhesion fibers, as revealed using inhibitor Y-27632. Another Rho-kinase inhibitor, HA-1077 or Fasudil, is currently used in the treatment of cerebral vasospasm; the related nanomolar inhibitor H-1152P improves on its selectivity and potency.

Mutants of protein kinase A that mimic the ATP-binding site of protein kinase B (AKT).

The mutation of well behaved enzymes in order to simulate less manageable cognates is the obvious approach to study specific features of the recalcitrant target. Accordingly, the prototypical protein kinase PKA serves as a model for many kinases, including the closely related PKB, an AGC family protein kinase now implicated as oncogenic in several cancers. Two residues that differ between the alpha isoforms of PKA and PKB at the adenine-binding site generate differing shapes of the binding surface and are likely to play a role in ligand selectivity.

Phosphorylation and flexibility of cyclic-AMP-dependent protein kinase (PKA) using (31)P NMR spectroscopy.

Cell signaling pathways rely on phosphotransfer reactions that are catalyzed by protein kinases. The protein kinases themselves are typically regulated by phosphorylation and concurrent structural rearrangements, both near the catalytic site and elsewhere. Thus, physiological function requires posttranslational modification and deformable structures.