Identification of 2 serine residues of MEK-1 that are differentially phosphorylated during activation by raf and MEK kinase.
The signal transduction kinase MEK (mitogen-activated protein (MAP) or extracellular signal-regulated (Erk) kinase)-1 is activated via phosphorylation by MEKK (MEK kinase) and raf kinases. We show here that these two kinases phosphorylate rat MEK-1 exclusively on two serine codons, Ser218 and Ser222. Phosphorylation of MEK-1 on serines 218 and 222 is both necessary and sufficient for MEK-1 to be activated and able to phosphorylate MAP kinase. A mutant form of MEK-1 that replaces these two codons with alanine cannot be activated, and one that substitutes glutamic acid residues in place of these 2 serines is active independent of activation by phosphorylation. These sites of activation occur in a region of MEK-1 that is similar to sites of activating phosphorylation in several other serine/threonine kinases, suggesting that this region may represent a conserved "activating domain" of many kinases. MEKK and raf display differences in site preference between these two codons, with MEKK showing preference for the amino acid at codon 218 and raf phosphorylating each residue approximately equally. This site preference might result in differences in the temporal or subsequent substrate patterns of MEK activation that result from these two activation pathways.
Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106.
M
M
Yan
D J
DJ
Templeton
D000595:Amino Acid Sequence; D000818:Animals; D004789:Enzyme Activation; D005971:Glutamates / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D048728:MAP Kinase Kinase Kinase 1; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D005971:Glutamates; D010455:Peptides; D011518:Proto-Oncogene Proteins; D010768:Phosphoserine; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048728:MAP Kinase Kinase Kinase 1; C482578:Map3k1 protein, mouse; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases