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The binding of myristoylated N-terminal nonapeptide from neuron-specific protein CAP-23/NAP-22 to calmodulin does not induce the globular structure observed for the calmodulin–nonmyristoylated peptide complex

Published online by Cambridge University Press:  15 December 2000

NOBUHIRO HAYASHI
Affiliation:
Division of Biomedical Polymer Science, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan
YOSHINOBU IZUMI
Affiliation:
Graduate School of Engineering, Yamagata University, Yonezawa 992-8510, Japan
KOITI TITANI
Affiliation:
Division of Biomedical Polymer Science, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan
NORIO MATSUSHIMA
Affiliation:
School of Health Sciences, Sapporo Medical University, S-1, W-17, Sapporo 060-8556, Japan
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Abstract

CAP-23/NAP-22, a neuron-specific protein kinase C substrate, is Nα-myristoylated and interacts with calmodulin (CaM) in the presence of Ca2+ ions. Takasaki et al. (1999, J Biol Chem 274:11848–11853) have recently found that the myristoylated N-terminal nonapeptide of CAP-23/NAP-22 (mC/N9) binds to Ca2+-bound CaM (Ca2+/CaM). In the present study, small-angle X-ray scattering was used to investigate structural changes of Ca2+/CaM induced by its binding to mC/N9 in solution. The binding of one mC/N9 molecule induced an insignificant structural change in Ca2+/CaM. The 1:1 complex appeared to retain the extended conformation much like that of Ca2+/CaM in isolation. However, it could be seen that the binding of two mC/N9 molecules induced a drastic structural change in Ca2+/CaM, followed by a slight structural change by the binding of more than two but less than four mC/N9 molecules. Under the saturated condition (the molar ratio of 1:4), the radius of gyration (Rg) for the Ca2+/CaM-mC/N9 complex was 19.8 ± 0.3 Å. This value was significantly smaller than that of Ca2+/CaM (21.9 ± 0.3 Å), which adopted a dumbbell structure and was conversely 2–3 Å larger than those of the complexes of Ca2+/CaM with the nonmyristoylated target peptides of myosin light chain kinase or CaM kinase II, which adopted a compact globular structure. The pair distance distribution function had no shoulder peak at around 40 Å, which was mainly due to the dumbbell structure. These results suggest that Ca2+/CaM interacts with Nα-myristoylated CAP-23/NAP-22 differently than it does with other nonmyristoylated target proteins. The N-terminal amino acid sequence alignment of CAP-23/NAP-22 and other myristoylated proteins suggests that the protein myristoylation plays important roles not only in the binding of CAP-23/NAP-22 to Ca2+/CaM, but also in the protein–protein interactions related to other myristoylated proteins.

Type
Research Article
Copyright
© 2000 The Protein Society

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