IDENTIFICATION OF -R-X-(X)-S T-X(3)-S/T- AS CONSENSUS SEQUENCE MOTIF FOR AUTOPHOSPHORYLATION-DEPENDENT PROTEIN-KINASE/

To identify consensus sequence motif for a new family of protein kinas e termed autophosphorylation-dependent protein serine/threonine kinase (auto-kinase), we have tested several synthetic peptides. The well es tablished protein serine/threonine kinases such as cAMP-dependent prot ein kinase, Ca2+/calmodulin-dependent protein kinase (CaM-kinase), and protein kinase C were found to be inactive toward phosphorylation of syntide-3 (RPRPASVPPSPSLSRHA), which turned out to be an excellent sub strate only for auto-kinase, indicating that syntide-3 is a specific s ubstrate for auto kinase. Modification of syntide-3 to become RPRPASVP PS/T did not affect the activity of auto-kinase. By contrast, autokina se became rather or almost inactive when the peptide was modified to b ecome RPRPASVPPA/G/F/K/R/D/E/Y, indicating that amino acid number 10 i n syntide-3 is crucial to the sequence motif recognized by auto-kinase . Phosphorylation of myelin basic protein (MBP) by autokinase revealed that auto-kinase predominantly phosphorylates MBP on one particular s ite with RTT(p)HYGS as the phosphorylation site sequence, which could not be phosphorylated by any other reported MBP kinases including cAMP -dependent protein kinase, CaM-kinase, protein kinase C, mitogen-activ ated protein kinase, and kinase FA/GSK-3. Taken together, the results provide initial evidence that -Arg-X-(X)-Ser/Thr-X(3)-Ser/Thr- may rep resent a unique consensus sequence motif specifically recognized by au tophosphorylation-dependent protein kinase, a new family of multisubst rate/multifunctional protein serine/threonine kinase.