Comparison of the solution conformations of a cell-adhesive peptide LBE and its reverse sequence EBL

T-cell adhesion is mediated by an ICAM-1/LFA-1 interaction; this interactio n plays a crucial role in T-cell activation during immune response. LBE pep tide, which is derived from the beta-subunit of LFA-1, has been shown to in hibit ICAM-1/LFA-1-mediated T-cell adhesion. In this work, we studied the s olution conformations of LBE peptide and its reverse sequence (EBL) by NMR, CD and molecular dynamics simulations. Reverse peptides have been used as controls in biological studies. The effect of reversing the sequence of LBE to EBL peptides on their respective conformations is important in understa nding their biological properties in vitro or in vivo. The NMR studies for these peptides were carried out in water and in TFE/water solvent systems. In 40% TFE/water, both peptides exhibited helical conformation. CD studies suggested that the LBE exhibits 30% helical conformation, while the EBL exh ibits 20% helical conformation. From the NMR and MD simulation studies, it was evident that the peptides exhibited a stable helical conformation; a st able helical structure was found at Leu6 to Leu15 for LBE and at Gly9 to Le u17 for EBL. The helical conformations of LBE and EBL may be in equilibrium with other possible conformers; the other conformers contain loop and rum structures. Both peptides bind to divalent cations because the LBE is deriv ed from the cation-binding region of the LFA-1. This study shows that rever sing the peptide sequence did not alter the secondary structure of the corr esponding sequence. Hence, caution must be exercised when using reverse pep tides as controls in biological studies. This report will improve our abili ty to design a better inhibitor of ICAM-1/LFA-1 interaction.