Conformational analysis of biologically active truncated linear analogs ofendothelin-1 using NMR and molecular modeling

Some linear truncated analogs of endothelin-l display potent agonistic acti vity at the ETB receptor, especially when the side chain of Trp(21) is N-fo rmylated. Then, the three-dimensional arrangements of six structurally redu ced linear analogs, three formylated and three nonformylated, have been inv estigated by high resolution NMR spectroscopy and molecular modeling, in or der to pinpoint the conformational features related to the biological activ ity. Two-dimensional double-quantum-filtered correlation spectroscopy (DQFC OSY), total correlation spectroscopy (TOCSY) and nuclear Overhauser enhance ment spectroscopy (NOESY) were recorded and analyzed for each molecule. Int erspatial distance constraints were derived from the intensity of the NOESY connectivities. The formation of hydrogen bonding was monitored from the t emperature dependence of the NH chemical shifts. Molecular models calculate d by means of: distance geometry, simulated annealing and energy minimizati on, using the NMR constraints, strongly suggested a global elongated struct ure for the formylated analogs exhibiting biological activity, and a folded arrangement for the unformylated derivatives. Homology comparisons allowed the identification of a beta -turn-like folding of the C-terminal segment Asp(18)-Trp(21) as a probable key-factor for activity.