A pickup in pseudokinase activity

Kinases catalyse the phosphorylation of target substrates on hydroxy group-containing residues as a means to nucleate multi-component complexes or to stabilize unique conformational states. Through this biochemical activity, kinases play critical roles in many signal transduction and disease pathways. Pseudokinases constitute a subclass of these enzymes that were originally predicted as inactive on the basis of mutations of key conserved active-site residues. However, recent biochemical and structural analyses have revealed several enzymatically active pseudokinases, suggesting either that novel mechanisms of phosphorylation are at play or that the constraints for highly conserved active-site residues are looser than originally anticipated. The purpose of the present review is to summarize several of the active pseudokinases, and one in particular termed KSR (kinase suppressor of Ras), which was recently found to possess a kinase activity that can become accelerated through an allosteric mechanism. Utilization of catalytic activity or structural features of the kinase fold may be key to the function of many pseudokinases.