Tryptophan mutants of intestinal XXXX -binding protein: ultraviolet absorption and circular dichroism studies.

@entity815 @entity844 @entity54044 @entity18811
An UV absorption and CD study of intestinal @entity844 -binding protein is presented. Since there are only two Trp residues in the molecule, two single-Trp mutants were prepared to deconvolute their signals. The individual contribution of the eight @entity815 and four Tyr residues was not established; however, @entity815 global contribution is relatively free of interferences from the other chromophores and was observed directly. CD spectra showed that @entity815 vibronic structure was unusually sharp and seems to monitor very specific details in the three-dimensional structure. The global signal from Tyr was assigned only approximately due to band broadening and overlapping. At the upper end of the CD spectrum, strong positive (1)L(b) Trp transitions from Trp 82 and strong negative (1)L(b) Trp transitions from @entity18811 were observed. (1)L(a) transitions were overall weak, positive for Trp 82 and negative for @entity18811 , nearly cancelling each other out in the final spectrum. The above assignment is of practical and fundamental interest to monitor folding, binding, and molecular dynamics down to microdomain resolution. The assignment of Trp bands allowed comparison with previous data from @entity54044 , another member of the IFABP family with 28% identical residues. It was found that structural homology extends beyond sequence and tertiary fold to include optical properties of equivalent Trp residues in the structure.
