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

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• CD8 is a crucial T cell coreceptor binding to pHLA I, essential for cytotoxic T lymphocyte activation.
• Soluble CD8 alphaalpha can inhibit T cell activation but requires high concentrations due to low pHLA I affinity.

Purpose of the Study:

• To design and produce a mutated soluble CD8 alphaalpha with enhanced binding affinity for pHLA I.
• To characterize the binding and structural properties of the high-affinity CD8 mutant.

Main Methods:

• Protein engineering to create a high-affinity CD8 alphaalpha mutant.
• Surface plasmon resonance (SPR) for binding characterization.
• X-ray crystallography to determine the mutant's structure at 2.1 A resolution.

Main Results:

• A mutated soluble CD8 alphaalpha exhibiting approximately fourfold higher affinity for pHLA I was successfully produced.
• Structural analysis revealed that increased affinity is mediated by an optimized interaction between the HLA alpha3 loop and mutated CD8 CDR-like loops.
• The mutation involves a larger side chain facilitating enhanced contact with the HLA alpha3 loop.

Conclusions:

• The engineered high-affinity CD8 alphaalpha mutant demonstrates improved binding to pHLA I.
• This enhanced binding is structurally explained by optimized molecular interactions.
• The findings suggest potential for developing more effective CD8-based therapeutics for T cell-related conditions.