dirigent proteins

[Pankaj Jaiswal]

Hi,

What i figured out about this enzyme is 

"Dirigent protein in the presence of an oxidase or one electron oxidant, effects
stereoselective bimolecular phenoxy radical coupling in vitro. Itself lacking a
catalytically active (oxidative) center, its mechanism of action is presumed to
involve capture of E-coniferyl alcohol-derived free-radical intermediates, with
consequent stereoselective coupling to give (+)-pinoresinol." PMID: 8994027

definition: Lacking catalytic active site, the protein in the presence of an
oxidase or one electron oxidant, effects stereoselective bimolecular phenoxy
radical coupling, thus becoming a part of holozyme. Best characterised as a
function during lignan biosynthesis.
term name: stereoselective coupling (as function) 
synonym:dirigent protein



instance of "enzyme regulator" (GO:0030234) as Michael suggested

First I thought about it as a isomerase/racemase, but since its not responsible
for this kind of an activity it can go as an enzyme regulator. Though its
clearly a part of oxidase carrying out the reaction converting E-coniferyl
alcohol to a(+)-pinoresinol


"Michael Ashburner (Genetics)" wrote:
> 
> Sorry to be so long in replying to this:
> 
> I think that we need a new function term for dirigent proteins.  I have done
> some reading and suggest this new term:
> 
> guiding stereospecific synthesis ; GO:??????? ; synonym:dirigent protein
> 
> definition: The orientation of free radical substrates in such a way that
> only a particular stereoisomer is synthesised by an enzyme. Best characterised
> as a function during lignan biosynthesis.
> 
> It is not clear where this should go, but I suggest that it could be a
> direct child of "enzyme regulator" (GO:0030234) whose definition is
> "Modulates the activity of an enzyme."
> 
> Feedback please.
> 
> Michael
> 
> > From owner-gofriends at genome.stanford.edu Thu Jun 13 18:51:43 2002
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> > From: "Hannick, Linda" <lhannick at tigr.org>
> > To: geneontology-term-request at lists.sourceforge.net,
> >         "Smith, Roger"
> >        <rsmith at tigr.org>
> > Cc: Midori A Harris <midori at genome.Stanford.EDU>, gofriend at genome.Stanford.EDU
> > Date: Thu, 13 Jun 2002 13:50:08 -0400
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> >
> > We are currently looking at dirigent proteins, and are not experts in lignan
> > biosynthesis.  Maybe someone with more expertise in this field can help us
> > come up with a GO term to accurately describe the function of this protein
> > and where it fits in the DAG (GO:0009807 accurately describes the process
> > that it is involved in).
> >
> > Dirigent proteins, in the presence of an oxidase or one electron oxidant,
> > affect stereoselective biomolecular phenoxy radical coupling (See Gang et
> > al. (1999) Chem Biol 6, 143-151).  They do not have a catalytically active
> > (oxidative) center, but they orient free radical substrates in such a way
> > that random coupling cannot occur, and only the 8-8'-coupled intermediate
> > (+)-pinoresinol is formed.  Any suggestions on where this should be added?
> >
> > Thanks
> > Roger Smith
> > The Institute for Genomic Research
> > Bioinformatics Analyst
> > rsmith at tigr.org
> >
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > Linda I. Hannick, Ph.D.
> > The Institute for Genomic Research
> > Bioinformatics Analyst
> > 9712 Medical Center Drive
> > Rockville  MD  20850
> > ~~~~~~~~~~~~~~~~~~~~
> >
> > 301-838-5857 voice
> > 301-838-0208 fax
> > lhannick at tigr.org
> >
> 
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-- 

******************************************
Pankaj Jaiswal, Ph.D.                                   
Postdoctoral Associate
Dept. of Plant Breeding                             
Cornell University                                   
Ithaca, NY-14853, USA   

Tel:+1-607-255-3103 / Fax:+1-607-255-6683
E mail: pj37 at cornell.edu
http://www.gramene.org   
******************************************

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