Specificity and symmetry in the interaction of calmodulin domains with the skeletal muscle myosin light chain kinase target sequence.
The specificity of interaction of the isolated N- and C-terminal domains of calmodulin with peptide WFFp (Ac-KRRWKKNFIAVSAANRFK-amide) and variants of the target sequence of skeletal muscle myosin light chain kinase was investigated using CD and fluorescence. Titrations show that two molecules of either domain bind to 18-residue target peptides. For WFFp, the C-domain binds with 4-fold higher affinity to the native compared with the non-native site; the N-domain shows similar affinity for either site. The selectivity of the C-domain suggests that it promotes occupancy of the correct binding site for intact calmodulin on the target sequence. Far UV CD spectra show the extra helicity induced in forming the 2:1 C-domain-peptide or the 1:1:1 C-domain-N-domain-peptide complex is similar to that induced by calmodulin itself; binding of the C-domain to the Trp-4 site is essential for developing the full helicity. Calmodulin-MLCK-peptide complexes show an approximate two-fold rotational relationship between the two highly homologous domains, and the 2:1 C (or N)-domain-peptide complexes evidently have a similar rotational symmetry. This implies that a given domain can bind sequences with opposite peptide polarities, significantly increasing the possible range of conformations of calmodulin in its complexes, and extending the versatility and diversity of calmodulin-target interactions.
Barth
A
A
Division of Physical Biochemistry, National Institute for Medical Research, London, United Kingdom.
Martin
S R
SR
Bayley
P M
PM
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002942:Circular Dichroism; D004331:Drosophila melanogaster; D004789:Enzyme Activation; D004926:Escherichia coli; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000201:enzymology; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
D002147:Calmodulin; D009842:Oligopeptides; D009219:Myosin-Light-Chain Kinase; D002118:Calcium