SOLUTION STRUCTURE BY SITE-DIRECTED TRYPTOPHAN FLUORESCENCE IN TEAR LIPOCALIN

The solution structure of the G strand of human tear lipocalin was ded uced by site directed tryptophan fluorescence (SDTF). The fluorescent amino acid, tryptophan, was sequentially substituted for each native a mino acid in the sequence of the G strand. The fluorescent properties resolved alternating periodicity as predicted for beta sheet structure , twists in the beta sheet, strand orientation in the lipocalin cavity , and the relative depth of residues in the cavity. A distribution of microstates with various orientations of dipoles in the side chain env ironments of the G strand revealed mobility on the nanosecond time sca le, SDTF is broadly applicable to most proteins and will complement x- ray crystallography, site directed spin labeling by electron paramagne tic resonance (EPR), and nuclear magnetic resonance (NMR) in the deter mination of solution structure. (C) 1997 Academic Press.