Tyrosine-phosphorylated calmodulin has reduced biological activity.
Calmodulin is phosphorylated by the purified insulin receptor on tyrosine residues with a maximum stoichiometry of 1 mol phosphate/mol of calmodulin. Isolated tryptic phosphopeptides were sequenced by manual Edman degradation and demonstrated that calmodulin is equally phosphorylated on tyrosine 99 and tyrosine 138. Phosphorylated calmodulin has a decreased affinity (K0.5 = 4.2 nM) for the 63-kDa isozyme of cyclic nucleotide phosphodiesterase compared to nonphosphorylated calmodulin (K0.5 = 2.1 nM). The K0.5 for Ca2+ is marginally increased from 2.8 to 3.2 microM in the presence of phosphotyrosyl calmodulin. The effect of the calmodulin antagonist, mastoparan, was investigated to determine whether mastoparan would differentially inhibit calmodulin- or phosphocalmodulin-dependent enzyme activity. The IC50 of mastoparan is fourfold lower for phosphotyrosyl calmodulin compared to nonphosphorylated calmodulin. Phosphorylation of calmodulin may provide a mechanism for the differential regulation of calmodulin-dependent enzymes. These observations further support a potentially important regulatory function of calmodulin phosphorylation in signal transduction.
Williams
J P
JP
University of Alabama at Birmingham, Department of Pathology 35294-0007.
Jo
H
H
Sacks
D B
DB
Crimmins
D L
DL
Thoma
R S
RS
Hunnicutt
R E
RE
Radding
W
W
Sharma
R K
RK
McDonald
J M
JM
D000595:Amino Acid Sequence; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D036341:Intercellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009712:Nucleotides, Cyclic / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry; D010455:Peptides; D010748:Phosphopeptides / Q000737:chemistry / Q000302:isolation & purification; D010727:Phosphoric Diester Hydrolases / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine; D011972:Receptor, Insulin / Q000378:metabolism*; D017421:Sequence Analysis; D014443:Tyrosine / Q000031:analogs & derivatives / Q000302:isolation & purification / Q000378:metabolism*; D014862:Wasp Venoms / Q000494:pharmacology
D002147:Calmodulin; D036341:Intercellular Signaling Peptides and Proteins; D009712:Nucleotides, Cyclic; D010446:Peptide Fragments; D010455:Peptides; D010748:Phosphopeptides; D014862:Wasp Venoms; D019000:Phosphotyrosine; D014443:Tyrosine; C037500:mastoparan; D011972:Receptor, Insulin; D010727:Phosphoric Diester Hydrolases; D002118:Calcium