3S5L

Crystal structure of CD4 mutant bound to HLA-DR1

Summary for 3S5L

• Entry DOI: 10.2210/pdb3s5l/pdb
• Related: 3S4S
• Descriptor: HLA class II histocompatibility antigen, DR alpha chain, HLA class II histocompatibility antigen DR beta chain, HA peptide, ... (6 entities in total)
• Functional Keywords: protein-protein complex, immune system, co-receptor
• Biological source: Homo sapiens (human); More
• Cellular location: Cell membrane; Single-pass type I membrane protein: P01903 D7RIG0 3S5L
• Total number of polymer chains: 8
• Total formula weight: 133883.16

Authors

Li, Y. (deposition date: 2011-05-23, release date: 2011-09-21, Last modification date: 2023-09-13)

Primary citation

Wang, X.X.,Li, Y.,Yin, Y.,Mo, M.,Wang, Q.,Gao, W.,Wang, L.,Mariuzza, R.A.
Affinity maturation of human CD4 by yeast surface display and crystal structure of a CD4-HLA-DR1 complex.
Proc.Natl.Acad.Sci.USA, 108:15960-15965, 2011

PubMed Abstract: Helper T-cell activation generally requires the coreceptor CD4, which binds MHC class II molecules. A remarkable feature of the CD4-MHC class II interaction is its exceptionally low affinity, which ranges from K(D) = ∼200 μM to >2 mM. Investigating the biological role of the much lower affinity of this interaction than those of other cell-cell recognition molecules will require CD4 mutants with enhanced binding to MHC class II for testing in models of T-cell development. To this end, we used in vitro-directed evolution to increase the affinity of human CD4 for HLA-DR1. A mutant CD4 library was displayed on the surface of yeast and selected using HLA-DR1 tetramers or monomers, resulting in isolation of a CD4 clone containing 11 mutations. Reversion mutagenesis showed that most of the affinity increase derived from just two substitutions, Gln40Tyr and Thr45Trp. A CD4 variant bearing these mutations bound HLA-DR1 with K(D) = 8.8 μM, compared with >400 μM for wild-type CD4. To understand the basis for improved affinity, we determined the structure of this CD4 variant in complex with HLA-DR1 to 2.4 Å resolution. The structure provides an atomic-level description of the CD4-binding site on MHC class II and reveals how CD4 recognizes highly polymorphic HLA-DR, -DP, and -DQ molecules by targeting invariant residues in their α2 and β2 domains. In addition, the CD4 mutants reported here constitute unique tools for probing the influence of CD4 affinity on T-cell activation and development.

PubMed: 21900604
DOI: 10.1073/pnas.1109438108

Experimental method

X-RAY DIFFRACTION (2.1 Å)