Classical and Nonclassical Class I Major Histocompatibility Complex Molecules Exhibit Subtle Conformational Differences That Affect Binding to CD8αα
2000; Elsevier BV; Volume: 275; Issue: 20 Linguagem: Inglês
10.1074/jbc.275.20.15232
ISSN1083-351X
AutoresGeorge F. Gao, Benjamin E. Willcox, Jessica R. Wyer, Jonathan M. Boulter, Christopher A. O'Callaghan, Katsumi Maenaka, David I. Stuart, E. Yvonne Jones, P. Anton van der Merwe, John I. Bell, Bent K. Jakobsen,
Tópico(s)Reproductive System and Pregnancy
ResumoThe cell surface molecules CD4 and CD8 greatly enhance the sensitivity of T-cell antigen recognition, acting as “co-receptors” by binding to the same major histocompatibility complex (MHC) molecules as the T-cell receptor (TCR). Here we use surface plasmon resonance to study the binding of CD8αα to class I MHC molecules. CD8αα bound the classical MHC molecules HLA-A*0201, -A*1101, -B*3501, and -C*0702 with dissociation constants (K d) of 90–220 μm, a range of affinities distinctly lower than that of TCR/peptide-MHC interaction. We suggest such affinities apply to most CD8αα/classical class I MHC interactions and may be optimal for T-cell recognition. In contrast, CD8αα bound both HLA-A*6801 and B*4801 with a significantly lower affinity (≥1 mm), consistent with the finding that interactions with these alleles are unable to mediate cell-cell adhesion. Interestingly, CD8αα bound normally to the nonclassical MHC molecule HLA-G (K d ∼150 μm), but only weakly to the natural killer cell receptor ligand HLA-E (K d ≥ 1 mm). Site-directed mutagenesis experiments revealed that variation in CD8αα binding affinity can be explained by amino acid differences within the α3 domain. Taken together with crystallographic studies, these results indicate that subtle conformational changes in the solvent exposed α3 domain loop (residues 223–229) can account for the differential ability of both classical and nonclassical class I MHC molecules to bind CD8. The cell surface molecules CD4 and CD8 greatly enhance the sensitivity of T-cell antigen recognition, acting as “co-receptors” by binding to the same major histocompatibility complex (MHC) molecules as the T-cell receptor (TCR). Here we use surface plasmon resonance to study the binding of CD8αα to class I MHC molecules. CD8αα bound the classical MHC molecules HLA-A*0201, -A*1101, -B*3501, and -C*0702 with dissociation constants (K d) of 90–220 μm, a range of affinities distinctly lower than that of TCR/peptide-MHC interaction. We suggest such affinities apply to most CD8αα/classical class I MHC interactions and may be optimal for T-cell recognition. In contrast, CD8αα bound both HLA-A*6801 and B*4801 with a significantly lower affinity (≥1 mm), consistent with the finding that interactions with these alleles are unable to mediate cell-cell adhesion. Interestingly, CD8αα bound normally to the nonclassical MHC molecule HLA-G (K d ∼150 μm), but only weakly to the natural killer cell receptor ligand HLA-E (K d ≥ 1 mm). Site-directed mutagenesis experiments revealed that variation in CD8αα binding affinity can be explained by amino acid differences within the α3 domain. Taken together with crystallographic studies, these results indicate that subtle conformational changes in the solvent exposed α3 domain loop (residues 223–229) can account for the differential ability of both classical and nonclassical class I MHC molecules to bind CD8. cytotoxic T lymphocytes T-cell receptor surface plasmon resonance major histocompatibility complex T-cell recognition, nonclassical class I MHC molecules resonance unit(s) Cytotoxic T lymphocytes (CTL)1 expressing the cell surface glycoprotein CD8 play an important role in immune protection against intracellular pathogens such as viruses. CD8 greatly enhances antigen recognition by CTL (1.Janeway Jr., C.A. Annu. Rev. Immunol. 1992; 10: 645-674Crossref PubMed Scopus (491) Google Scholar) and is referred to as a co-receptor, since it binds to the same peptide-major histocompatibility complex class I molecules as the T-cell receptor (TCR) (1.Janeway Jr., C.A. Annu. Rev. Immunol. 1992; 10: 645-674Crossref PubMed Scopus (491) Google Scholar). Generation of mature CTL also depends upon the presence of CD8 at their surface (2.Fung Leung W.P. Schilham M.W. Rahemtulla A. Kundig T.M. Vollenweider M. Potter J. van Ewijk W. Mak T.W. Cell. 1991; 65: 443-449Abstract Full Text PDF PubMed Scopus (463) Google Scholar) and upon the interaction of CD8 with MHC (3.Zuniga Pflucker J.C. Jones L.A. Chin L.T. Kruisbeek A.M. Semin. Immunol. 1991; 3: 167-175PubMed Google Scholar, 4.Aldrich C.J. Hammer R.E. Jones-Youngblood S. Koszinowski U. Hood L. Stroynowski I. Forman J. Nature. 1991; 352: 718-721Crossref PubMed Scopus (76) Google Scholar). CD8 exists at the cell surface as a homodimer of two α chains (CD8αα) and as a heterodimer or an α and a β chain (CD8αβ). Expression of the heterodimeric form of CD8 is limited to the αβ T-cell population, whereas homodimeric CD8αα is present not only on αβ T-cells but also on subsets of γδ T cells and natural killer (NK) cells (5.Moebius U. Kober G. Griscelli A.L. Hercend T. Meuer S.C. Eur. J. Immunol. 1991; 21: 1793-1800Crossref PubMed Scopus (145) Google Scholar).Direct binding of CD8αα to classical MHC alleles was initially demonstrated using cell-cell adhesion assays (6.Norment A.M. Salter R.D. Parham P. Engelhard V.H. Littman D.R. Nature. 1988; 336: 79-81Crossref PubMed Scopus (372) Google Scholar). Mutagenesis data suggested that CD8 and the TCR bind to separate sites on the MHC molecule (7.Salter R.D. Benjamin R.J. Wesley P.K. Buxton S.E. Garrett T.P. Clayberger C. Krensky A.M. Norment A.M. Littman D.R. Parham P. Nature. 1990; 345: 41-46Crossref PubMed Scopus (472) Google Scholar). Recently, crystal structures of human and murine CD8αα-MHC complexes (8.Gao G.F. Tormo J. Gerth U.C. Wyer J.R. McMichael A.J. Stuart D.I. Bell J.I. Jones E.Y. Jakobsen B.K. Nature. 1997; 387: 630-634Crossref PubMed Scopus (374) Google Scholar, 9.Kern P.S. Teng M.K. Smolyar A. Liu J.H. Liu J. Hussey R.E. Spoerl R. Chang H.C. Reinherz E.L. Wang J.H. Immunity. 1998; 9: 519-530Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar) have shown that CD8αα binds to an extended site on classical MHC molecules, which includes nonpolymorphic residues from the α2 and α3 domain as well as β2-microglobulin. The two CD8α subunits contact the α3 domain in a manner resembling antibody-antigen interaction, with their complementarity determining region-like loops forming a pocket which accommodates an exposed loop (residues 223–229) linking the C and D strands. This mode of interaction prevents the simultaneous binding of a second MHC molecule to CD8αα. Furthermore, the crystal structure also indicates that the binding of CD8αα does not induce any significant changes in the TCR-binding platform of the MHC. We have recently studied the interaction of soluble forms of these molecules by surface plasmon resonance (10.Wyer J.R. Willcox B.E. Gao G.F. Gerth U.C. Davis S.J. Bell J.I. van der Merwe P.A. Jakobsen B.K. Immunity. 1999; 10: 219-225Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). Despite the large binding interface (total surface area buried upon binding ∼2000 Å2), CD8αα binds HLA-A2 with an extremely low affinity (K d ∼200 μm). In agreement with the structural studies, binding of CD8αα to HLA-A2-peptide did not affect the binding of a TCR to the same peptide-MHC complex (10.Wyer J.R. Willcox B.E. Gao G.F. Gerth U.C. Davis S.J. Bell J.I. van der Merwe P.A. Jakobsen B.K. Immunity. 1999; 10: 219-225Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar).To investigate further the mechanism of co-receptor function, we have determined the extent to which the affinity of CD8/class I MHC interactions varies, by analyzing the binding of CD8αα to HLA-A, -B, and -C molecules. The genes that encode these classical MHC molecules are the most polymorphic human genes described (11.Parham P. Lomen C.E. Lawlor D.A. Ways J.P. Holmes N. Coppin H.L. Salter R.D. Wan A.M. Ennis P.D. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 4005-4009Crossref PubMed Scopus (347) Google Scholar). While CD8αα can bind to most classical MHC alleles, there is evidence that some alleles, such as HLA-A68 and -B48, possess polymorphisms in the α3 domain, which make them especially poor ligands for the co-receptor (12.Salter R.D. Norment A.M. Chen B.P. Clayberger C. Krensky A.M. Littman D.R. Parham P. Nature. 1989; 338: 345-347Crossref PubMed Scopus (222) Google Scholar, 13.Martinez-Naves E. Barber L.D. Madrigal J.A. Vullo C.M. Clayberger C. Lyu S.C. Williams R.C. Gorodezky C. Markow T. Petzl-Erler M.L. Parham P. Tissue Antigens. 1997; 50: 258-264Crossref PubMed Scopus (24) Google Scholar). Therefore CD8αα binding to a number of different alleles, including HLA-A68 and -B48, was tested. Also, since our understanding of the interaction of CD8 with nonclassical MHC molecules is limited, the binding of CD8αα to the nonclassical class I MHC molecules HLA-E and HLA-G was investigated. Site-directed mutagenesis was used to establish the molecular basis of the observed differences in CD8αα binding. Cytotoxic T lymphocytes (CTL)1 expressing the cell surface glycoprotein CD8 play an important role in immune protection against intracellular pathogens such as viruses. CD8 greatly enhances antigen recognition by CTL (1.Janeway Jr., C.A. Annu. Rev. Immunol. 1992; 10: 645-674Crossref PubMed Scopus (491) Google Scholar) and is referred to as a co-receptor, since it binds to the same peptide-major histocompatibility complex class I molecules as the T-cell receptor (TCR) (1.Janeway Jr., C.A. Annu. Rev. Immunol. 1992; 10: 645-674Crossref PubMed Scopus (491) Google Scholar). Generation of mature CTL also depends upon the presence of CD8 at their surface (2.Fung Leung W.P. Schilham M.W. Rahemtulla A. Kundig T.M. Vollenweider M. Potter J. van Ewijk W. Mak T.W. Cell. 1991; 65: 443-449Abstract Full Text PDF PubMed Scopus (463) Google Scholar) and upon the interaction of CD8 with MHC (3.Zuniga Pflucker J.C. Jones L.A. Chin L.T. Kruisbeek A.M. Semin. Immunol. 1991; 3: 167-175PubMed Google Scholar, 4.Aldrich C.J. Hammer R.E. Jones-Youngblood S. Koszinowski U. Hood L. Stroynowski I. Forman J. Nature. 1991; 352: 718-721Crossref PubMed Scopus (76) Google Scholar). CD8 exists at the cell surface as a homodimer of two α chains (CD8αα) and as a heterodimer or an α and a β chain (CD8αβ). Expression of the heterodimeric form of CD8 is limited to the αβ T-cell population, whereas homodimeric CD8αα is present not only on αβ T-cells but also on subsets of γδ T cells and natural killer (NK) cells (5.Moebius U. Kober G. Griscelli A.L. Hercend T. Meuer S.C. Eur. J. Immunol. 1991; 21: 1793-1800Crossref PubMed Scopus (145) Google Scholar). Direct binding of CD8αα to classical MHC alleles was initially demonstrated using cell-cell adhesion assays (6.Norment A.M. Salter R.D. Parham P. Engelhard V.H. Littman D.R. Nature. 1988; 336: 79-81Crossref PubMed Scopus (372) Google Scholar). Mutagenesis data suggested that CD8 and the TCR bind to separate sites on the MHC molecule (7.Salter R.D. Benjamin R.J. Wesley P.K. Buxton S.E. Garrett T.P. Clayberger C. Krensky A.M. Norment A.M. Littman D.R. Parham P. Nature. 1990; 345: 41-46Crossref PubMed Scopus (472) Google Scholar). Recently, crystal structures of human and murine CD8αα-MHC complexes (8.Gao G.F. Tormo J. Gerth U.C. Wyer J.R. McMichael A.J. Stuart D.I. Bell J.I. Jones E.Y. Jakobsen B.K. Nature. 1997; 387: 630-634Crossref PubMed Scopus (374) Google Scholar, 9.Kern P.S. Teng M.K. Smolyar A. Liu J.H. Liu J. Hussey R.E. Spoerl R. Chang H.C. Reinherz E.L. Wang J.H. Immunity. 1998; 9: 519-530Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar) have shown that CD8αα binds to an extended site on classical MHC molecules, which includes nonpolymorphic residues from the α2 and α3 domain as well as β2-microglobulin. The two CD8α subunits contact the α3 domain in a manner resembling antibody-antigen interaction, with their complementarity determining region-like loops forming a pocket which accommodates an exposed loop (residues 223–229) linking the C and D strands. This mode of interaction prevents the simultaneous binding of a second MHC molecule to CD8αα. Furthermore, the crystal structure also indicates that the binding of CD8αα does not induce any significant changes in the TCR-binding platform of the MHC. We have recently studied the interaction of soluble forms of these molecules by surface plasmon resonance (10.Wyer J.R. Willcox B.E. Gao G.F. Gerth U.C. Davis S.J. Bell J.I. van der Merwe P.A. Jakobsen B.K. Immunity. 1999; 10: 219-225Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). Despite the large binding interface (total surface area buried upon binding ∼2000 Å2), CD8αα binds HLA-A2 with an extremely low affinity (K d ∼200 μm). In agreement with the structural studies, binding of CD8αα to HLA-A2-peptide did not affect the binding of a TCR to the same peptide-MHC complex (10.Wyer J.R. Willcox B.E. Gao G.F. Gerth U.C. Davis S.J. Bell J.I. van der Merwe P.A. Jakobsen B.K. Immunity. 1999; 10: 219-225Abstract Full Text Full Text PDF PubMed Scopus (164) Google Scholar). To investigate further the mechanism of co-receptor function, we have determined the extent to which the affinity of CD8/class I MHC interactions varies, by analyzing the binding of CD8αα to HLA-A, -B, and -C molecules. The genes that encode these classical MHC molecules are the most polymorphic human genes described (11.Parham P. Lomen C.E. Lawlor D.A. Ways J.P. Holmes N. Coppin H.L. Salter R.D. Wan A.M. Ennis P.D. Proc. Natl. Acad. Sci. U. S. A. 1988; 85: 4005-4009Crossref PubMed Scopus (347) Google Scholar). While CD8αα can bind to most classical MHC alleles, there is evidence that some alleles, such as HLA-A68 and -B48, possess polymorphisms in the α3 domain, which make them especially poor ligands for the co-receptor (12.Salter R.D. Norment A.M. Chen B.P. Clayberger C. Krensky A.M. Littman D.R. Parham P. Nature. 1989; 338: 345-347Crossref PubMed Scopus (222) Google Scholar, 13.Martinez-Naves E. Barber L.D. Madrigal J.A. Vullo C.M. Clayberger C. Lyu S.C. Williams R.C. Gorodezky C. Markow T. Petzl-Erler M.L. Parham P. Tissue Antigens. 1997; 50: 258-264Crossref PubMed Scopus (24) Google Scholar). Therefore CD8αα binding to a number of different alleles, including HLA-A68 and -B48, was tested. Also, since our understanding of the interaction of CD8 with nonclassical MHC molecules is limited, the binding of CD8αα to the nonclassical class I MHC molecules HLA-E and HLA-G was investigated. Site-directed mutagenesis was used to establish the molecular basis of the observed differences in CD8αα binding. We thank Linda Barber, David Allen, Liz Davies, Gavin Wright, Marion Brown, Pokrath Hansasuta, David Bainbridge, Shirley Ellis, Graham Ogg, Veronique Braud, and Andrew McMichael for generously providing materials and valuable advice.
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