PRECISION SUBSTRATE TARGETING OF PROTEIN-KINASES V-ABL AND C-SRC

The active site substrate specificities of v-Abl and c-Src are compare d and contrasted, Both enzymes catalyze the phosphorylation of a broad assortment of peptide-bound aliphatic and aromatic alcohols, such as achiral and simple straight chain residues, In addition, both protein kinases exhibit a ''dual specificity'' with respect to the ability to utilize D- and L-configurational isomers as substrates, However, c-Src and v-Abl are extremely inefficient as catalysts for certain structur al arrangements, including secondary alcohols and primary alcohols con taining large substituents in close proximity to the hydroxyl moiety. In addition to these similarities, these enzymes also display notewort hy differences in catalytic behavior, Whereas c-Src exhibits a modest preference for aromatic versus aliphatic alcohols, v-Abl does not, Mos t dramatic is the ability of c-Src to utilize short chain alcohols as substrates, an activity virtually absent from the catalytic repertoire of v-Abl, The implications of these observations are 2-fold. First, b ecause both enzymes are able to accommodate a wide variety of structur al variants within their respective active site regions, there exists a substantial degree of flexibility with respect to inhibitor design, Second, because these enzymes exhibit disparate active site specificit ies, it is possible that other tyrosine-specific protein kinases will display unique substrate specificities as well, Consequently, it may u ltimately be possible to exploit these differences to generate inhibit ors that precisely target specific protein kinases.