Dear Yuli
The paper is very nice in my opinion. Its strength is probably in the interactions between the drug and
TnC, and less in the detailed mechanism of the conformational change.
I think I would rather point out more explicitely how similar
after all the cardiac and skeletal TnC are going to be upon binding to TnI ... since that is what
is the most interesting aspect of the TnC function. The two step activation you are mentioning
is fine in vitro... I am not sure it really has effect in vivo since TnI (the target) and TnC
are always so near one another. I think there is no similarity whatsoever between the pre-semi open lobe of apo-Cterm Clobe of CaM and
the Ca2+-bound N-lobe of cTnC. This shows in fact by the angle measured between helices. What the
NMR structure shows is that binding in one of the EF-hand is not enough to open the lobe. I would have
studied more profoundly than you did why is that and my guess is that this is due to the interactions between
the linker 1 (in the N-lobe) and the D-helix of TnC that are specific to TnC and stronger than those observed
for other EF-hand proteins. I think this is an important point for the function of TnC because it makes sure
the N-lobe sharpens the requirement for Ca2+ and makes sure that TnC doesn't open even if Ca2+ is close
to concentrations that would allow it to open for other proteins such as CaM. In other words, since
TnI and TnC are always close to one another, it is critical for TnC to find a way to make sure that its
target doesn't have the power to force the lobe open and interact. My guess is that the interactions between
the linker 1 of TnC and the D-helix are critical for that and are also the reason why in cTnC one sees that
binding of the Ca2+ in one lobe can't force open the EF-hand in the other lobe. I am not sure that bindind of Ca2+ and then TnI sequentially as you are making a big statement about is that
interesting in vivo. I would guess both happen really quickly after one another and do not change much the
function of TnC and the regulation by Ca2+ of the troponin complex. I really don't think that the semi-open lobe has anything to do with your structure. If you want to put
the angles, you'll have to indicate to me the precise method you used (or give me access to the programs
you used) to measure these angles). I don't think you need this for your paper though. As written it is
a very confusing paragraph and I am not sure people will gather what you are trying to say. You can call me home tonite with C2 if you want more from me. Happy new year !
All my best wishes for your life ! Anne
yuli@brandeis.edu wrote: Dear Anne Have you received the coordinates? Thanks a lot and happy new year Yu Li -- Dr. Anne Houdusse Juille Equipe ATIPE - Motilite Structurale INSTITUT CURIE - Section de recherche UMR 144 du CNRS 26, rue d'ULM 75248 Paris cedex 05 Tel: 33- 1- 42-34-63-92 Fax: 33- 1- 42-34-63-82 Anne.Houdusse@curie.fr