Molecular dissection of the CD2-CD58 counter-receptor interface identifiesCD2 Tyr86 and CD58 Lys34 residues as the functional "hot spot"

The heterophilic CD2-CD58 adhesion interface contains interdigitating resid ues that impart high specificity and rapid binding kinetics. To define the hot spot of this counter-receptor interaction, we characterized CD2 adhesio n domain variants harboring a single mutation of the central Tyr86 or of ea ch amino acid residue forming a salt link/hydrogen bond. Alanine mutations at D31, D32 and K34 on the C strand and K43 and R48 on the C' strand reduce affinity for CD58 by 47-127-fold as measured by isothermal titration calor imetry. The Y86A mutant reduces affinity by similar to 1000-fold, whereas Y 86F is virtually without effect, underscoring the importance of the phenyl ring rather than the hydroxyl moiety. The CD2CD58 crystal structure offers a detailed view of this kev functional epitope: CD2 D31 and D32 orient the side-chain of CD58 Kj4 such that CD2 Y86 makes hydrophobic contact with the extended aliphatic component of CD58 K34 between CD2 Y86 and CD58 F46. The elucidation of this hot spot provides a new target for rational design of immunosuppressive compounds and suggests a general approach for other recep tors. (C) 2001 Academic Press.