Site-specific phosphorylation and point mutations of telokin modulate its Ca2+-desensitizing effect in smooth muscle

J Biol Chem. 2001 Jul 6;276(27):24519-24. doi: 10.1074/jbc.M103560200. Epub 2001 May 9.


Forskolin and 8-bromoguanosine 3'-5'-cyclic monophosphate (8-Br-cGMP) induce phosphorylation of Ser-13 of telokin and relaxation of smooth muscle at constant calcium. Comparison with the effect of wild type with aspartate (D; to mimic phosphorylation) and alanine (A; non-phosphorylatable) mutants of telokin showed that the S13D mutant was more effective than wild type in relaxing smooth muscle at constant calcium. The efficacy of the Ser-13A, S12A, and S12D mutants was not significantly different from that of wild-type telokin. The effect of neither S13D nor Ser-13A was affected by 8-Br-cGMP, whereas the effect of wild type, S12A, and S12D was enhanced by 8-Br-cGMP, indicating the specificity of Ser-13 charge modification. Mutation of Ser-19 (a mitogen-activated protein kinase site) showed the S19A to be more effective than, and S19D to be not different from, wild-type telokin. The effect of both mutants was slightly enhanced by 8-Br-cGMP. A truncated (residues 1-142) form lacking the acidic C terminus had the same relaxant effect as wild-type telokin, whereas the C-terminal peptide (residues 142-155) had no effect. We conclude that site-specific modification of the N terminus modulates the Ca2+ -desensitizing effect of telokin on force.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Aspartic Acid / metabolism
  • Binding Sites
  • Calcium / metabolism*
  • Colforsin / pharmacology
  • Culture Techniques
  • Cyclic GMP / analogs & derivatives
  • Cyclic GMP / pharmacology
  • Ileum / drug effects
  • Ileum / metabolism
  • Microcystins
  • Microscopy, Electron
  • Muscle Proteins / genetics*
  • Muscle Proteins / metabolism*
  • Muscle Relaxation / drug effects
  • Muscle, Smooth / drug effects*
  • Muscle, Smooth / metabolism
  • Muscle, Smooth / ultrastructure
  • Myosin-Light-Chain Kinase
  • Peptide Fragments
  • Peptides
  • Peptides, Cyclic / pharmacology
  • Phosphorylation
  • Point Mutation*
  • Rabbits
  • Serine / metabolism


  • Microcystins
  • Muscle Proteins
  • Peptide Fragments
  • Peptides
  • Peptides, Cyclic
  • Colforsin
  • Aspartic Acid
  • 8-bromocyclic GMP
  • telokin
  • Serine
  • microcystin
  • Myosin-Light-Chain Kinase
  • Cyclic GMP
  • Calcium