Yes, it is electrostatic interaction. But when searching for a salt-bridge
in a protein structure it won't be considered a significant non-bonded
interactions at 8 A distance. Also, the electrostatic interaction extends
beyond 8 A. For a significant interaction the distance need to be < 8A.
Ibrahim
On 10/16/08 12:10 PM, "Nadir T. Mrabet" <[log in to unmask]>
wrote:
> --
>
> Pr. Nadir T. Mrabet
> Cellular & Molecular Biochemistry
> INSERM U-724
> Nancy University, School of Medicine
> 9, Avenue de la Foret de Haye, BP 184
> 54505 Vandoeuvre-les-Nancy Cedex
> France
> Phone: +33 (0)3.83.68.32.73
> Fax: +33 (0)3.83.68.32.79
> E-mail: [log in to unmask]
>
>
> Hi,
>
> Salt bridges (or ion pairs) can be long-range (up to 7-8 Ang). They obey
> Coulomb's law.
> In contrast, H-bonds are short-range and are further anisotropic.
>
> For those with general interest in electrostatics, I suggest to go back
> to the
> 1978 paper of Max Perutz:
> Electrostatic Effects in Proteins
> Science (1978) 201 (4362), 1187-1191.
>
> Nadir Mrabet
>
> Jayashankar wrote:
>> Dear Fransico,
>>
>> *Salt bridges are close range electrostatic interaction which depend
>> on conformer population.
>>
>> *S.Jayashankar
>> Research Student
>> Institute for Biophysical Chemistry
>> Hannover Medical School
>> Germany.
>>
>>
>> On Thu, Oct 16, 2008 at 8:21 AM, Chavas Leo <[log in to unmask]
>> <mailto:[log in to unmask]>> wrote:
>>
>> Dear Francisco --
>>
>> On 15 Oct 2008, at 17:05, Francisco J. Enguita wrote:
>>>
>>> how
>>>
>>> can you define a salt-bridge within a protein structure ?
>>>
>>
>> According to Wikipedia:
>> a salt bridge in proteins is "a relatively weak ionic bond between
>> positively and negatively charged side-chains of proteins."
>>
>> Now, at far as I understand (based on "Structure and Mechanism in
>> Protein Science - Alan Fersht), you have a salt bridge when two
>> groups are making an hydrogen bond that is favored by
>> electrostatic interaction, electrostatic energies being weak in
>> water. To quote the author of the book, let say you have the
>> following equilibrium:
>>
>> E-NH3+ ------- OH2 + OH2 ------- -O2C-S <==> E-NH3+
>> ------- -O2C-S + H2O ------- H2O
>>
>> The right-hand side equation would be more "favorable", as the
>> electrostatic interaction will be more stable than in the
>> left-hand side where both ions would be in contact with water
>> molecules.
>>
>> HTH
>>
>> Kind regards.
>>
>> -- Leo --
>> ------------------------------------------------------------
>> Chavas Leonard, Ph.D. @ home
>> Research Associate
>> Marie Curie Actions Fellow
>> ------------------------------------------------------------
>> Faculty of Life Sciences
>> The University of Manchester
>> The Michael Smith Building
>> Oxford Road
>> Manchester Lancashire
>> M13 9PT
>> ------------------------------------------------------------
>> Tel: +44(0)161-275-1586
>> e-mail: [log in to unmask]
>> <mailto:[log in to unmask]>
>> http://personalpages.manchester.ac.uk/staff/leonard.chavas/
>>
>>
>>
>
|