It's probably best to look at the structure separately - using the structural restraints derived from the NMR data - NOE', J-couplings, etc. The 13C shift of glutamate C-delta atoms alone won't give the answer.

Maybe it is possible to change the pH, while monitoring NOEs and couplings?

As glutamate becomes protonated, the structural changes may happen as well - so it may be both.

Are the two changes, the protonation and change in conformation occuring simulatneously or is it question of finding out which one of the two factors is contributing to chemical shifts/variations in the shifts.

In such cases it may be better to ascertain the posssible trends/magnitudes of changes for the two causes etc., by a theoretical calculation of the relevant approximate geometries and try to follow the experimentally observed variations based on the possibilities. The guessed structure or theoretical values may not be reproducing experimental values accuartely but certain inferences can be helpful instead of relyin only the analysis of experimental spectra. look up some of the observations in my posters at crsi-13nsc and nmrs2011 at the following URL: 13nsc and nmrs2011

http://www.ugc-inno-nehu.com/crsi13nscnmrs2011.html

Aravamudhan