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Determination of the dipole moments of RNAse SA wild type and a basic mutant
Author(s) -
Chari Ravi,
Singh Shubhadra N.,
Yadav Sandeep,
Brems David N.,
Kalonia Devendra S.
Publication year - 2012
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.24006
Subject(s) - dipole , chemistry , bond dipole moment , debye , transition dipole moment , isoelectric point , rnase p , moment (physics) , wild type , mutant , electric dipole moment , atomic physics , molecular physics , physics , enzyme , rna , biochemistry , quantum mechanics , gene , organic chemistry
In this study, we report the effects of acidic to basic residue point mutations (5K) on the dipole moment of RNAse SA at different pHs. Dipole moments were determined by measuring solution capacitance of the wild type (WT) and the 5K mutant with an impedance analyzer. The dipole moments were then (1) compared with theoretically calculated dipole moments, (2) analyzed to determine the effect of the point mutations, and (3) analyzed for their contribution to overall protein–protein interactions (PPI) in solution as quantitated by experimentally derived second virial coefficients. We determined that experimental and calculated dipoles were in reasonable agreement. Differences are likely due to local motions of residue side chains, which are not accounted for by the calculated dipole. We observed that the proteins' dipole moments increase as the pH is shifted further from their isoelectric points and that the wild‐type dipole moments were greater than those of the 5K. This is likely due to an increase in the proportion of one charge (either negative or positive) relative to the other. A greater charge disparity corresponded to a larger dipole moment. Finally, the larger dipole moments of the WT resulted in greater attractive overall PPI for that protein as compared to the 5K. Proteins 2011; © 2011 Wiley Periodicals, Inc.