Re: [ccp4bb]: non-flat tyrosine

["S. Ravichandran" <ravi@cmb2.saha.ernet.in>]

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Hi,

> I have a high resolution structure in which I have a tyrosine where the
> zeta carbon and the hydroxyl group is tilted a little bit and is not
> exactly in the same plane as the ring. When I look at 3 sigma, the
> density clearly supports this. Can this be the case or is it just my
> eyes that needs some maintenance ?

I can think of two possibilities:

(1) It is reported that at high radiation doses, the Tyr side-chain can
loose its -OH group [Ref: Burmeister et al. (2000). Acta Cryst D56,
328-341]. Such structural damage is pretty clearly seen at high resolution
(whether or not you flash-cool the crystal).

(2) Sometimes, at ultra-high resolution, you may have a non-ideal geometry
deviating away from your (Engh & Huber) small molecule stereochemistry.  
There is nothing to worry about it.. if resolution says everything!

Cheers,
Ravi.

======================================================================
|S.Ravichandran (Graduate student)  |E-mail: ravi@cmb2.saha.ernet.in |
|Crystallogr. & Mol. Biology Div.   |FAX:    (91)(033)-337-4637      |
|Saha Institute of Nuclear Physics  |                                |
|I/AF, Bidhan Nagar, Calcutta 700064|                                | 
|INDIA.      URL:- http://www-bsg.saha.ernet.in/ravi.html            |
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