Computcational design and crystal structure of an enhanced affinity mutant human CD8 alpha alpha coreceptor

Human CD8 is a T cell coreceptor, which binds to pHLA I and plays a pivotal role in the activation of cytotoxic T lymphocytes. Soluble recombinant CD8 alpha alpha has been shown to antagonize T cell activation, both in vitro and in vivo. However, because of a very low affinity for pHLA 1, high concentrations of soluble CD8 alpha alpha are required for efficient inhibition. Based upon our knowledge of the wild-type CD8/pHLA I structure, we have designed and produced a mutated form of soluble CD8 alpha alpha that binds to pHLA I with approximately fourfold. higher affinity. We have characterized the binding of the high affinity CD8 mutant using surface plasmon resonance and determined its structure at 2.1 angstrom resolution using X-ray crystallography. The analysis of this structure suggests that the higher affinity is achieved by providing a larger side chain that allows for an optimal contact to be made between the HLA alpha 3 loop and the mutated CDR-like loops of CD8. Proteins 2007;67:65-74. (c) 2007 Wiley-Liss, Inc.