Structural and ICAM-1-docking properties of a cyclic peptide from the I-domain of LFA-1: An inhibitor of ICAM-1/LFA-1-mediated T-cell adhesion

The purpose of this work was to study the conformation of cyclic peptide 1, cyclo(1,12)Pen] -Ile2-Thr3-Asp4-Gly5-Glu6-Ala7-Thr8-Asp9-Ser10-Gly11-Cys12-OH, derived from the 1-domain of the LFA-1 alpha-subunit, We found that cyclic peptide I can bind to the D1-domain of ICAM-1 and inhibit ICAM-1/LFA-1-mediated homotypic and heterotypic T-cell adhesion. To understand the bioactive conformation and binding requirements for cyclic peptide 1, its solution structure was studied using NMR, CD. and molecular dynamics simulations. Furthermore, possible binding proper-ties between the cyclic peptide and the D1-domain of ICAM-I were evaluated using docking experiments. This cyclic peptide has a stable betaII'-turn at Asp4-Gly5-Glu6-Ala7 and a betaI-turn at Pen1-Ile2-Thr3-Asp4; a less stable betaV-turn is found at the C-terminal region. The beta-turn at Asp4-Gly5-Glu6-Ala7 was also found in the X-ray structure of the 1-domain of LFA-1. Our CD studies showed that the peptide binds to calcium/magnesium and forms a 1:1 (peptide:calcium/magnesium) complex with low cation concentrations and multiple types of complexes with higher cation concentrations. Binding to divalent cations causes a conformational change in peptide 1; this is consistent with our previous study that binding of peptide 1 to ICAM-1 was influenced by divalent cations. Docking studies show the interaction between cyclic peptide 1 and the D1-domain of ICAM-1 it indicates that the Ile2-Thr3-Asp4-Gly4-Glu6-Ala7-Thr8 sequence interacts with the F and C strands of the D I-domain. Finally, these studies will help us design a new generation of selective peptides that may bind better to the D1-domain of ICAM-1.