Computational design and crystal structure of an enhanced affinity mutant human CD8 αα coreceptor

AbstractHuman 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 αα has been shown to antagonize T cell activation, both in vitro and in vivo. However, because of a very low affinity for pHLA I, high concentrations of soluble CD8 αα 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 αα 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 Å 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 α3 loop and the mutated CDR‐like loops of CD8. Proteins 2007. © 2007 Wiley‐Liss, Inc.