CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
Stochastic study of the Effect of Ionic Strength on Non-Covalent Interactions in Protein Pores
Qitao Zhao 1, Dilani A Jayawardhana 1 and Xiyun Guan 1*
1 The University of Texas at Arlington
* To whom correspondence should be addressed. E-mail: xguan{at}uta.edu.
Submitted on July 16, 2007
Revised on August 25, 2007
Accepted on 18 October 2007
 |
Abstract |
|---|
Salt plays a critical role in the physiological activities of cells. Here we demonstrate that ionic strength significantly affects the kinetics of non-covalent interactions in protein channels, as observed in stochastic studies of the transfer of various analytes through pores of wild-type and mutant alpha-hemolysin proteins. As the ionic strength increased, the association rate constant of electrostatic interactions was accelerated, while those of both hydrophobic and aromatic interactions were retarded. Dramatic decreases in the dissociation rate constants, and thus increases in the overall reaction formation constants, were observed for all non-covalent interactions studied. The results suggest that with the increase of salt concentration, the streaming potentials for all the protein pores decrease, while the preferential selectivities of the pores for either cations or anions drop. Furthermore, results also demonstrate that the salt effect on the rate of association of analytes to a pore differs significantly depending on the nature of the non-covalent interactions occurring in the protein channel. In addition to providing new insights into the nature of analyte-protein pore interactions, the salt-dependence of non-covalent interactions in protein pores observed provides a useful means to greatly enhance the sensitivity of the nanopore, which may find useful application in stochastic sensing.
Key Words:
alpha-hemolysin, charge selectivity, ionic strength, kinetics, non-covalent interactions, stochastic sensing
