The BION-1/D4β_c interface.

D4β_c is shown as a surface representation colored according to the functional effect of residue substitution. Blue represents residues whose substitution abrogates binding of BION-1 but does not affect affinity-conversion. Red represents residues whose substitution reduces affinity-conversion but does not affect binding of BION-1. Yellow represents residues whose substitution does not affect binding of BION-1 or cytokines. Gray represents residues that have not been examined by mutation and do not contact BION-1. The identities of key D4β_c residues are shown in italics. Residues in BION-1 that contact D4β_c are shown in stick representation and colored cyan blue (hydrophilic) or brown (hydrophobic-aromatic). The backbone atoms of residues colored gray show the connectivity of the loops.