Richard
Not sure about chains but mutual hydrogen bonded networks (you mention
networks) between protein, water (and ligand) surely occur. I think most
self respecting waters would try and form more then two hydrogen bonds
(rather then just be part of a chain) though one might not see all the
(perhaps transient) bonds in an x-ray structure. These networks seem to
form very easily in computer simulations where their dynamic behavior
can be studied. Lots on "spanning water networks". So waters could link
residues a considerable distance away but some of these waters might
also join to other residues (the mutual hydrogen bonded network).

Of course you are asking about direct x-ray evidence and this is more
difficult. Fig. 1 in
http://www.lsbu.ac.uk/water/protein.html gives an example. I would hope
there are more recent ones which others will identify more easily than I
can.

Colin

-Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
Richard Gillilan
Sent: 17 June 2008 20:05
To: [log in to unmask]
Subject: [ccp4bb] Structural importance of ordered water?

Direct hydrogen bonds between sidechains are obviously important to
structural stability in proteins. From time to time I see cases of
water-mediated bonds in which a single water molecule seems to play an
important role (sometimes taking the place of a missing ligand atom in
an apo structure, for example). But what about larger chains and
networks of water? Assuming a structure is high enough in resolution and
well-ordered enough to observe such things, has anyone systematically
studied the structural importance of multiple water interactions (I do
know of a paper by Faerman and Karplus back in 94, but perhaps there is
more recent work).

Has anyone here ever seen a plausible argument that a chain of several
hydrogen-bonded waters enables residue A to interact with residue B,
some considerable distance away?

I have to say, I am skeptical of arguments based on water positions.

Thanks

Richard Gillilan
MacCHESS
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