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[ccp4bb]: Summary: Met as Zn ligand? Metal-site databases.

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A Summary of responses to my recent question:
> Dear all,
> Is there any example in which a protein binds Zn++
> via methionine SD?
> or, Is there any way to search the PDB with unix commands like
>         grep LINK *.pdb |grep MET |grep ZN
> if you don't have a local copy of the PDB?
> I've tried searching the HAD at http://www.bmm.icnet.uk/had/ ,
> but it doesn't seem to be fully functional yet.
> --
> Ed
Andy Arvai, Marieke Thayer, and Tom Brett referred me to the Metalloprotein DB 
at Scripps: 
Miriam Hirshberg  to ReliBase:
	and also performed the "grep" on their local PDB.
Flip Hoedemaeker referred me to the Jena site database:

Of these the Jena database was the easiest to use, just enter Zn and Met
in the residues textbox and submit. It found no example, but many hits
with Cu + Met or Zn + Cys, verifying the serch procedure.

The Scripps database found 1 trivial example in which the Zn is bound to
mainchain atoms of Met: 1b0n

Miriam Hirshberg wrote a script to search their local PDB for occurrence
of ZN and MET together in LINK records. There were no hits found
(1b0n has no LINK records!).

Herbert Nar referred me to Azurin structures in which the metal has 
been switched. Native has Cu, with a 3.0 A bond to MET SD.
When replaced with Zn, Met 121 is no longer coordinated to the Zn.
(This from abstract of Nar et al. 1992, Eu. J. B. 205, 1123)
So it looks as if Met doesn't bind Zn, which seems reasonable enough.
Zn is in the same column of the periodic chart as Hg, which Petsko says
doesn't react with methionines. All the zincs I've seen so far bind to
cys or his (or in 1b0n to the mainchain N and O of a methionine). 

I have this strong anomalous peak at the Zn edge in a sample soaked with 
ZnCl2, and its next to a highly conserved MET (so I don't think its a 
sequencing error) The distance is a little too long for a S-Zn bond 
(~ 2.0 A in SOD) though, so maybe there's another atom between.
Thanks to all who responded,