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Salt bridge exchange binding mechanism between streptavidin and its DNA aptamer - thermodynamics and spectroscopic evidences.
MedLine Citation:
PMID:  23345105     Owner:  NLM     Status:  In-Data-Review    
Abstract/OtherAbstract:
Protein-nucleic acids binding driven by electrostatic interactions typically are characterized by the release of counter ions, and the salt-inhibited binding association constant (K(a) ) and the magnitude of exothermic binding enthalpy (ΔH). Here, we report a non-classical thermodynamics of streptavidin (SA)-aptamer binding in NaCl (140-350 mM) solutions near room temperatures (23-27 °C). By using isothermal titration calorimetry (ITC) and circular dichroism (CD)/fluorescence spectroscopy, we found that the binding was enthalpy driven with a large entropy cost (ΔH -20.58 kcal mol(-1) , TΔS -10.99 kcal mol(-1) , and K(a) 1.08 × 10(7)  M(-1) at 140 mM NaCl 25 °C). With the raise of salt concentrations, the ΔH became more exothermic, yet the K(a) was almost unchanged (ΔH -26.29 kcal mol(-1) and K(a) 1.50 × 10(7)  M(-1) at 350 mM NaCl 25 °C). The data suggest that no counter Na(+) was released in the binding. Spectroscopy data suggest that the binding, with a stoichiometry of 2, was accompanied with substantial conformational changes on SA, and the changes were insensitive to the variation of salt concentrations. To account for the non-classical results, we propose a salt bridge exchange model. The intramolecular binding-site salt bridge(s) of the free SA and the charged phosphate group of aptamers re-organize to form the binding complex by forming a new intermolecular salt bridge(s). The salt bridge exchange binding process requires minimum amount of counter ions releasing but dehydration of the contacting surface of SA and the aptamer. The energy required for dehydration is reduced in the case of binding solution with higher salt concentration and account for the higher binding exothermic mainly. Copyright © 2013 John Wiley & Sons, Ltd.
Authors:
Tai-Chih Kuo; Peng-Chen Lee; Ching-Wei Tsai; Wen-Yih Chen
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of molecular recognition : JMR     Volume:  26     ISSN:  1099-1352     ISO Abbreviation:  J. Mol. Recognit.     Publication Date:  2013 Mar 
Date Detail:
Created Date:  2013-01-24     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9004580     Medline TA:  J Mol Recognit     Country:  England    
Other Details:
Languages:  eng     Pagination:  149-59     Citation Subset:  IM    
Copyright Information:
Copyright © 2013 John Wiley & Sons, Ltd.
Affiliation:
Department of Biochemistry, Taipei Medical University, Taipei, 11031, Taiwan.
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