realistic amino acid subst. models

[Marc Robinson]

Structure-based amino acid substitution matrices have been developped. I
know some articles that describe such matrices (there may be others):


Overington J., Johnson M.S., Sali A. & Blundell T.L. (1990) Tertiary structural 
constraints on protein evolutionary diversity: templates, key residues and structure 
prediction. Proc. R. Soc. Lond. B 241:132-145 

Overington J., Donnelly D., Johnson M.S., Sali A. & Blundell T.L. (1992) 
Environment-specific amino acid substitution tables: Tertiary templates and 
prediction of protein folds. Prot. Sci. 1:216-226 

Risler J.L., Delorme M.O., Delacroix H. & Henaut A. (1988) Amino acid substitutions 
in structurally related proteins a pattern recognition approach. 
J. Mol. Biol. 204:1019-1029 


Hope this helps,

Laurent Duret


================================================================
Laurent Duret			    duret at biomserv.univ-lyon1.fr
Tel: 	+33 72.44.81.42		    Fax:	+33 78.89.27.19
Laboratoire de Biometrie, Genetique et Biologie des Populations
Bat 741 - URA CNRS 243 Universite Claude Bernard - Lyon I
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69622 Villeurbanne cedex FRANCE
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In article 38556 at ac.dal.ca, aroger at ac.dal.ca writes:
>I'm interested in improving empirically-based amino acid
>substitution model for use in phylogenetic analysis. 
>
>One method which may improve upon existing models (like
>the Dayhoff models which programs like PROTDIST and
>PROTML use) is to determine whether the propensity
>of an amino acid (say X) to change to another amino acid
>(Y) depends upon the structural context in which it is
>found.  For instance, it may be the case that the
>transition X<-->Y is very frequent in a secondary
>structural element like an alpha helix, but is very
>rare in a beta-sheet or a beta-turn.  Similarly
>a hydrophobic amino acid (lets call it Z) may
>frequently change to another hydrophobic amino acid (say Q (
>keep in mind that I'm not using the one-letter amino acid code))
>in a core region of a protein while the change to a charged
>or "hydrophilic" amino acid in this region may be very rare.
>The dynamics of change are likely going to be very different
>on a solvent accessible region of a protein.
>Thus it is possible that "averaged" substitution models
>like that of Dayhoff, may be very poor approximations of 
>the actual site by site frequencies simply because they
>are averages of many dissimilar models.
>
>If what I say is possibly true, it should be of interest
>to develop structure-based amino acid substitution matrices
>for a whole variety of proteins for which one of the homologues
>has been crystallized (making the assumption that the structures
>have not changed too much).  Doing this may allow us to develop
>general substitution matrices for structural elements and to
>test whether the different matrices are significantly
>different from one another (this may in turn help those
>interested in protein engineering) and in what way.
>The application of these models to protein phylogeny would
>only require the user, to provide structural information in addition
>to an alignment.
>
>Is someone already doing this?  Does anyone know of references
>to any such investigation?
>
>I'd be interested to hear what those involved in development of
>phylogenetic methods have to say about this idea
>
>Cheers
>Andrew Roger
>Dept. of Biochemistry
>Halifax, N.S.
>B3H 4H7
>aroger at ac.dal.ca