Peptides 24 (2003) 827–835 Solution structure of a peptide derived from the  subunit of LFA-1 Zhang Shuxing a , Wong S. Ying b , Teruna J. Siahaan c , Seetharama D.S. Jois a,∗ a Department of Pharmacy, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore b Department of Chemistry, National University of Singapore, 18 Science Drive 4, Singapore 117543, Singapore c Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence, KS 66047, USA Received 21 February 2003; accepted 15 May 2003 Abstract Cell-adhesion molecules are critical for immune response. It is well known that the inhibition of adhesion is very effective in immuno- therapy and that the peptides derived from leukocyte function associated antigen (LFA-1) and intercellular adhesion molecule (ICAM-1) modulate cell-adhesion interaction. The three-dimensional structure of a cyclic peptide, Cyclo(1,12)Pen 1 -Asp 2 -Leu 3 -Ser 4 -Tyr 5 -Ser 6 -Leu 7 - Asp 8 -Asp 9 -Leu 10 -Arg 11 -Cys 12 (cLBEL) derived from the  subunit of LFA-1 which is known to modulate homotypic T-cell-adhesion process has been studied using NMR, CD and molecular dynamics (MD) simulation. The peptide exhibits two possible conformations in solution. Structure I has a conformation with two consecutive -turns involving residues Tyr 5 -Ser 6 -Leu 7 -Asp 8 and Asp 9 -Leu 10 -Arg 11 -Cys 12 . Structure II has a -turn at Tyr 5 -Ser 6 -Leu 7 -Asp 8 and forms a -hairpin type of conformation. © 2003 Elsevier Inc. All rights reserved. Keywords: Leukocyte function associated antigen-1 (LFA-1); MIDAS domain; Peptide conformation; T-cell adhesion; -Turn 1. Introduction Accessory molecules play a major role in the cell-adhesion process, which is important for immune response. Leuko- cyte function associated antigen-1 (LFA-1) is one of the accessory molecules which binds to its ligand intercellular adhesion molecule-1 (ICAM-1) in the adhesion process and is responsible for the inflammatory and immune response [11,19,29,30]. Anti-adhesion therapy using antibodies to these accessory molecules has been used in developing therapeutic agents for autoimmune diseases like rheumatoid arthritis, diabetes and for the survival of transplanted organs [1,12,26]. In recent years, there have been a number of stud- ies on the use of antibodies to modulate LFA-1/ICAM-1 adhesion interaction. Promising results from such stud- ies have lead to the development of small molecules that might be used as anti-adhesive agents [18]. Our group and others have earlier shown that peptides derived from LFA-1 or ICAM-1 can modulate cell-adhesion interaction [8,13,27,33,34]. In order to understand how these peptide molecules modulate these interactions and to design bet- ter inhibitors of cell-adhesion process, we have studied the three-dimensional structure of LFA-1 derived peptides ∗ Corresponding author. Tel.: +65-6-874-2653; fax: +65-6-779-1554. E-mail address: phasdsj@nus.edu.sg (S.D.S. Jois). by NMR, CD, molecular dynamics (MD) simulations and energy minimization [14,15]. Here, we report our results on the structure of cLBEL peptide Cyclo(1,12)Pen 1 -Asp 2 -Leu 3 -Ser 4 -Tyr 5 -Ser 6 -Leu 7 - Asp 8 -Asp 9 -Leu 10 -Arg 11 -Cys 12 (cLBEL) derived from the -subunit of LFA-1 protein (sequence number 134–143). The peptide was cyclized by introducing penicillamine (Pen) and Cys at the N-terminal and C-terminal of the se- quence, respectively, and by forming a disulfide bond. Pen is used in position-1 because in previous work we have been successful in improving conformational stability of the cyclic peptide by using Pen at position 1 in the pep- tide sequence [13,34]. Penicillamine is also shown to be important in inducing conformational rigidity of the cyclic peptide [9]. Because the cLBEL peptide is derived from the -subunit I-like domain and can inhibit T-cell adhesion [33,34], the structure of this peptide may provide insight to the function of this sequence in ICAM-1/LFA-1 inter- action. There are several studies indicating that I-domain of LFA-1 and an allosteric domain from the -subunit are important in LFA-1/ICAM-1 interactions [4,10]. In the I-domain, the metal-ion dependent site (MIDAS) of the I-domain which is known to bind cations, seems to be important for ICAM-1/LFA-1 interactions [23]. However, the exact mechanism of the importance of -subunit mo- tif that is similar to I-domain in binding to ICAM-1 is not known. 0196-9781/$ – see front matter © 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0196-9781(03)00170-0