Subject: histidine state

From: "[email-masked]" <[email-masked]>
Date: Tue, 19 Mar 2002 03:53:49 -0500

Dear CCLers,

I have some questions regarding the state of histidine in proteins. I know that histidine can exist as with a weak positive charge in pH7, but also it might depend on the surrounding environment and neighbours. Is there a way that I can find out how the neighbouring residues can affect histidine? If I take my protein to be at pH7, can I assume that histidine will have a positive charge?  Both NE1 and ND1 will have hydrogens then. From what I've read, either one can be protonated or both will be. 
Also, from the structures that I've found, the double bonds exist in the side chain between CG=CD2 and ND1=CE1. Would the double bond exist for NE1=CE1 instead ? I would like to get more information about this as I'm not sure how to treat the histidine residues in my protein. 

Thank you for your time.

Regards,
Rowyna

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From: David van der Spoel <[email-masked]>
Date: Tue, 19 Mar 2002 14:02:01 +0100 (CET)

On Tue, 19 Mar 2002, [email-masked] wrote:

>Dear CCLers,
>
>I have some questions regarding the state of histidine in proteins. I 
>know that histidine can exist as with a weak positive charge in pH7, but 
>also it might depend on the surrounding environment and neighbours. Is 
>there a way that I can find out how the neighbouring residues can affect 
>histidine? If I take my protein to be at pH7, can I assume that histidine 
>will have a positive charge?  Both NE1 and ND1 will have hydrogens then. 
>From what I've read, either one can be protonated or both will be. 
In a protein you can check the hydrogen bonding network. In solution 90% 
is NE1 and 10% ND1 (at pH7)

Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
[email-masked]	[email-masked]   http://zorn.bmc.uu.se/~spoel
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