Sweet proteins retain their capability to interact with the sweet
taste receptor only when correctly folded. The possibility of their
usage as alternative sweeteners for food and beverages relies then
on the preservation of their 3D structure over a wide range of
physico-chemical conditions. Previous
structural studies, performed by CD and NMR spectroscopies in
solution at pH 7.0, revealed a high degree of similarity between
MNEI and the newly discovered sweeter mutant Y65R. In order to find the best conditions for future potential
alimentary applications, we have further investigated the structural
and functional behaviours of the two proteins in chemical
and physical conditions resembling those of common sweet drinks,
i.e. low pH and temperatures typical of coffee and fruit juices. Fig. 1
shows the overlay of far UV CD spectra at pH 3.3, 5.1 and 7.0 of
MNEI (panel A) and Y65R (panel B). Analysis of the spectra revealed
that under all the conditions explored both proteins retain very
similar secondary structure populations, characterised by a high
b-sheet and low a-helix content, coherently with the structure
determined by NMR studies at acidic and neutral pH for MNEI. Comparison of the
CD curves intensity, reported in Fig. 1, evidences a similar solubility
of the proteins at pH 5.1, but in agreement with data previously