Journal article
Paramecium Calmodulin Mutants Defective in Ion Channel Regulation Associate with Melittin in the Absence of Calcium but Require It for Tertiary Collapse
Biochemistry (Easton), Vol.40(4), pp.896-903
01/30/2001
DOI: 10.1021/bi0023091
PMID: 11170410
Abstract
Calmodulin (CaM) is a small acidic protein essential to calcium-mediated signal transduction. Conformational change driven by calcium binding controls its selective activation of myriad target proteins. In most well characterized cases, both homologous domains of CaM interact with a target protein. However, physiologically separable roles for the two domains were demonstrated by mutants of Paramecium tetraurelia [Kung, C. et al. (1992) Cell Calcium 13, 413], some of which have altered calcium affinities [Jaren, O. R. et al. (2000) Biochemistry 39, 6881]. To determine whether these mutants can associate with canonical targets in a calcium-dependent manner, their ability to bind melittin was assessed using analytical gel permeation chromatography, analytical ultracentrifugation, and fluorescence spectroscopy. The Stokes radius of wild-type PCaM and 11 of the mutants decreased dramatically upon binding melittin in the presence of calcium. Fluorescence spectra and sedimentation velocity studies showed that melittin bound to wild-type PCaM and mutants in a calcium-independent manner. However, there were domain-specific perturbations. Mutations in the N-domain of PCaM did not affect the spectrum of melittin (residue W19) under apo or calcium-saturated conditions, whereas most of the mutations in the C-domain did. These data are consistent with a calcium-dependent model of sequential target association whereby melittin (i) binds to the C-domain of PCaM in the absence of calcium, (ii) remains associated with the C-domain upon calcium binding to sites III and IV, and (iii) subsequently binds to the N-domain upon calcium binding to sites I and II of CaM, causing tertiary collapse.
Details
- Title: Subtitle
- Paramecium Calmodulin Mutants Defective in Ion Channel Regulation Associate with Melittin in the Absence of Calcium but Require It for Tertiary Collapse
- Creators
- Brenda R SorensenJason-Thomas EppelMadeline A Shea
- Resource Type
- Journal article
- Publication Details
- Biochemistry (Easton), Vol.40(4), pp.896-903
- Publisher
- American Chemical Society
- DOI
- 10.1021/bi0023091
- PMID
- 11170410
- ISSN
- 0006-2960
- eISSN
- 1520-4995
- Language
- English
- Date published
- 01/30/2001
- Academic Unit
- Molecular Physiology and Biophysics; Iowa Neuroscience Institute; Biochemistry and Molecular Biology
- Record Identifier
- 9984024410202771
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