Identification of the endogenous smooth muscle myosin phosphatase-associated kinase.
Ca(2+) sensitization of smooth muscle contraction involves inhibition of myosin light chain phosphatase (SMPP-1M) and enhanced myosin light chain phosphorylation. Inhibition of SMPP-1M is modulated through phosphorylation of the myosin targeting subunit (MYPT1) by either Rho-associated kinase (ROK) or an unknown SMPP-1M-associated kinase. Activated ROK is predominantly membrane-associated and its putative substrate, SMPP-1M, is mainly myofibrillar-associated. This raises a conundrum about the mechanism of interaction between these enzymes. We present ZIP-like kinase, identified by "mixed-peptide" Edman sequencing after affinity purification, as the previously unidentified SMPP-1M-associated kinase. ZIP-like kinase was shown to associate with MYPT1 and phosphorylate the inhibitory site in intact smooth muscle. Phosphorylation of ZIP-like kinase was associated with an increase in kinase activity during carbachol stimulation, suggesting that the enzyme may be a terminal member of a Ca(2+) sensitizing kinase cascade.
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Box 3813, Durham, NC 27710, USA.
J A
JA
MacDonald
M A
MA
Borman
A
A
Murányi
A V
AV
Somlyo
D J
DJ
Hartshorne
T A
TA
Haystead
D000595:Amino Acid Sequence; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002417:Cattle; D002852:Chromatography, Ion Exchange; D064550:Death-Associated Protein Kinases; D004591:Electrophoresis, Polyacrylamide Gel; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000201:enzymology*; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits
D051017:Apoptosis Regulatory Proteins; D064550:Death-Associated Protein Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases