According to the models of divergent molecular evolution, the evolvability of new protein function may depend on the induction of new phenotypic traits by a small number of mutations of the binding site residues. Evolutionary relationships between protein kinases are often employed to infer inhibitor binding profiles from sequence analysis. However, protein kinases binding profiles may display inhibitor selectivity within a given kinase subfamily, while exhibiting cross-activity between kinases that are phylogenetically remote from the prime target. The emerging insights into kinase function and evolution combined with a rapidly growing number of publically available crystal structures of protein kinases complexes have motivated structural bioinformatics analysis of sequence-structure relationships in determining the binding function of protein tyrosine kinases.