Affinity maturation of human CD4 by yeast surface display and crystal structure of a CD4-HLA-DR1 complex.

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TitleAffinity maturation of human CD4 by yeast surface display and crystal structure of a CD4-HLA-DR1 complex.
Publication TypeJournal Article
Year of Publication2011
AuthorsWang, XXiang, Li, Y, Yin, Y, Mo, M, Wang, Q, Gao, W, Wang, L, Mariuzza, RA
JournalProc Natl Acad Sci U S A
Date Published2011 Sep 20
KeywordsAmino Acid Sequence, Animals, Antigens, CD4, Binding Sites, Binding, Competitive, Cell Line, Crystallization, Crystallography, X-Ray, HIV Envelope Protein gp120, HLA-DR1 Antigen, Humans, Models, Molecular, Mutation, Peptide Library, Protein Binding, Protein Conformation, Protein Multimerization, Protein Structure, Tertiary, Sequence Homology, Amino Acid, Spodoptera, Surface Plasmon Resonance, Yeasts

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.

Alternate JournalProc. Natl. Acad. Sci. U.S.A.
PubMed ID21900604
PubMed Central IDPMC3179091
Grant ListAI036900 / AI / NIAID NIH HHS / United States
AI073654 / AI / NIAID NIH HHS / United States
P30 EB009998 / EB / NIBIB NIH HHS / United States