1 Graduate School of Genetic Resources Technology, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581 and 2 Department of Genetics, Medical Institute of Bioregulation, Kyushu University, Maidashi,Higashi-ku, Fukuoka 812-8582, Japan
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Keywords: analogue peptide/HLA class II molecule/molecular dynamics simulation/recognition/T cell receptor
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
As a model system to examine the molecular mechanisms of TCR antagonistic activities, we used the human class II HLA-DR4, peptide YWALEAAAD (Y = position 1, p1) and a T cell clone which recognizes an index peptide (YWALEAAAD) in the context of DRB1*0405 (Tana et al., 1998; Toh et al., 1998
). HLA-DRB1*0405 is one of the DR4-associated subtypes and strongly associated with rheumatoid arthritis (Kinouchi et al., 1994
; Matsushita et al., 1994
). To determine whether the analogue peptides which induced no proliferative responses of the T cell clone functioned as TCR antagonism, proliferation of the T cell clone for the index peptide bound to HLA-DR4 was tested in the presence of various concentrations of the analogue peptides. Based on the results of this investigation, we classified the analogue peptides into three groups, agonists, antagonists or null peptides (non-agonistic and non-antagonistic peptides) (Table I
). Analogue peptides carrying single residue substitutions at p3, p4, p5, p6, p7 or p8 in the index peptide were used.
|
|
The molecular dynamics (MD) simulation technique has the attractive feature that motions on the atomic level can be monitored and analyzed in atomic detail. To study the role of water molecules in the binding of peptides to MHC (Rognan et al., 1992a,b
; Meng et al., 1997
), to predict the binding epitope sequence (Rognan et al., 1994
; Lim et al., 1996
), to design the class I MHC ligands (Rognan et al., 1995
, Krebs et al., 1998
) and to explain the existing MHC-binding motifs (Hadida et al., 1995
; Rognan et al., 1997
; Steele et al., 1998
), the MD simulations methods have been used for MHCpeptide complexes.
In our previous work, we performed MD simulation of the DR4index peptide (YWALEAAAD) and DR4analogue peptide (agonists and antagonists) complexes. The root mean square (r.m.s.) deviation between two structures is a measure of their differences. The MD simulations showed that the r.m.s. deviations of the DR4antagonist complexes in the TCR-binding regions from the DR4index peptide complex were larger than those of the DR4agonist complexes. These results indicated that subtle changes of the TCR-binding regions on HLA molecule by the antagonist peptides could induce TCR antagonistic activities (Toh et al., 1998). We report here the results of additional MD simulations of the DR4analogue peptide (including null peptide) complexes. To analyze the principal determining factor in discriminating between the strong and the weak antagonists, we calculated the r.m.s. deviations from the index complex and the exposed areas of the side chains of the bound peptide. The results show that the weak antagonistic peptides could cause larger main chain shifts of the TCR-binding regions than do the strong antagonistic peptides. The simulations also indicate that the null peptides would be treated as completely different ligands mainly through the changes of the exposed side chains at p3, p5 or p7, rather than the conformational changes of the TCR-binding surfaces on the DR4 molecule.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
All simulations were performed using the InsightII/Discover software package (Molecular Simulations, San Diego, CA). The starting structure for all simulations of the DR4 complexes was the X-ray crystal structure of HLADRB1*0401 complex with a peptide derived from human collagen II (Protein Data Bank entry 2SEB; Dessen et al., 1997). Hydrogen atoms were added to this model using the InsightII program. To save computational time, only antigen-binding sites (3
84, ß3ß94) were taken into account in the study. This approximation was shown not to alter the accuracy of molecular dynamics simulations because only limited interactions exist between the
1ß1 and
2ß2 domains that do not significantly influence the shape of the peptide-binding groove (Rognan et al., 1992a
). DRB1*0405collagen peptide complex was constructed by replacement of two DRß residues (DRß57 and DRß71) that differ between DRB1*0401 and DRB1*0405. A peptide (NH2AAYWALEAAADAACOOH) and all analogue peptides bound to DRB1*0405 molecule were similarly generated from the backbone of the bound collagen peptide (residues 11681180), QYMRADQAAGGLR, co-crystallized with DRB1*0401 by substituting by corresponding residues.
Molecular mechanics and dynamics simulation protocol
Calculations were performed using the Discover 95.0 program. The parameter used was the consistent valence force field (CVFF). No cross-terms were used in the energy expression and a simple harmonic valence potential was used to model the valence bond stretching term. The minimized structures were solvated by a 10.0 Å layer of water molecules using the SOAK option of InsightII. For the water molecule the SPC model was used (Hermans et al., 1984; Berendesen et al., 1987
). During the molecular dynamics and minimization, a dielectric constant of 1.0 was used. Before the MD simulations were started, we performed energy minimizations in a four-step procedure: (1) the coordinates of all the protein atoms were fixed and solvent molecules were minimized using the steepest descent method (in all constrained minimizations for up to 1000 iterations); (2) the heavy chain atoms were tethered loosely (10 kcal/mol.Å2) while the hydrogen atoms were adjusted; (3) the backbone atoms were tethered loosely (10 kcal/mol.Å2) while the side chain was adjusted; (4) finally, the conjugated gradients minimizations were performed with all atoms free to move until the maximum derivative was <0.5 kcal/mol.Å. The minimized coordinates were used as a starting point for NVT (constant volume and temperature) molecular dynamics at 300 K to generate possible stable conformations. The system was warmed to 300 K. Bond lengths were constrained to equilibrium values during the simulations using the RATTLE method with a tolerance of 105 (Andersen, 1983
). For the treatment of the non-bond interactions, the cell multipole method (CMM) was used. The CMM is more rigorous and efficient than the application of cut-offs (Ding et al., 1992
; Mathiowetz et al., 1994
; Sugita and Kitao, 1998
). After a 10 ps equilibration stage, the simulations were continued at 300 K for 590 ps using a 2.0 fs time step. The simulations were carried out using the Verlet velocity algorithm (Swope and Anderson, 1982
) and the structures were stored in the computer every 1.0 ps. Acquired data were analyzed during the last 300 ps of the 600 ps simulation. Initially, we defined an average atomic conformation of the DR4index peptide (YWALEAAAD) complex during the last 300 ps of the simulation as an `index complex'.
Solvent-accessible surface areas
Solvent-accessible surface areas were computed for the structures during the last 300 ps of the simulations. The Connolly algorithm with a solvent probe radius of 1.4 Å was used (Connolly, 1983).
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
To study the basis for the observed phenomena, molecular dynamics simulations of DR4 (DRB1*0405)analogue peptide complexes were carried out for 600 ps. A standard way to evaluate the quality of an MD simulation is to monitor the r.m.s. deviations of protein atoms from the starting structure. Figure 2 shows the r.m.s. positional deviations of the C
atoms of DR4peptide complexes from each starting structure. Slight fluctuations were observed, but the r.m.s. deviations were stable around a constant value over the last 300 ps of the trajectory. Acquired data were analyzed during the last 300 ps of the 600 ps simulation.
|
In the proposed TCR-binding regions on the DR4 molecule, the r.m.s. deviations for C traces between the index complex and DR4analogue peptides (p3, p4, p5, p6, p7 and p8) complexes were computed (Figure 3
). The r.m.s. deviations of the antagonist complexes were larger than those of the agonists complexes, as reported previously (Toh et al., 1998
).
|
The p3 side chain contacts with open pocket in the binding site. The effects of the substitutions at p3 on the ß1 -helix were hardly found. In the simulations of the p3Leu (a weak antagonist) complex, the calculated r.m.s. deviations were higher than those of the p3Val (a strong antagonist) complex (Figure 3A
). The p3Leu side chain was more buried than other p3 side chains, indicating the buried portion at pocket 3 induces the structural changes of the TCR binding region (Figure 4
). In the p3Phe (a weak antagonist) complex, the r.m.s. deviations were comparable to those of the p3Gly (an agonist) complex. The p3Phe side chain, however, was more exposed to solvent (Figure 4
). In the p3agonist and p3antagonist complexes, ligands with more exposed side chain at p3 tended to be the weak antagonists (Figure 4
). A large portion of the p4 side chain (about 20% residue exposure) is buried in a hydrophobic pocket. In the simulation of the p4variants, the r.m.s. deviations of the p4Tyr (a weak antagonist) were higher than those of other p4variants (Figure 3B
). The p4Tyr side chain was too large to fit into pocket 4. Thus, the ß1
-helix between ß53 and ß73 shifted. The p6 side chain is buried in small pocket. In the p6variants, the r.m.s. deviations of the p6Val (a weak antagonist) were higher than those of other p6variants (Figure 3C
) and the
1
-helix near pocket 6 fluctuated. In the solvent-accessible areas of the p6 side chains in the p6variants, there were no remarkable differences (Figure 4
). The p7 side chain is partly buried in a shallow pocket 7. The p7 side chains in both the index and the p7agonist complexes were much less exposed in pocket 7 (Figure 4
). In the p7weak antagonist complexes, the r.m.s. deviations were much higher than those of the other p7variants (Figure 3D
). A wider range of C
deviations of the p7antagonist complexes was observed throughout the simulation. The r.m.s. deviations of the p7variants were higher than those of the p3, p4, p6 and p8variants, indicating that substitutions at p7 have a relatively larger influence to alter conformations of the TCR-binding sites than those at other positions (Figure 3
). The ß-chain helical region around pocket 7 which exhibits high temperature factors in all class II MHC structures was flexible. This flexible regions around pocket 7 induced the larger effects at p7 (Figure 5
). The p8 side chain projects into solvent. In the p8variants, a smaller range of C
deviations was observed throughout the simulation than the other variants (Figure 3
). The calculated r.m.s. deviations of the p8Asp (a weak antagonist) were much higher than those of the other p8variants. In the p8antagonist complexes, small shifts occurred in the location of the
1
-helix between
53 and
61, but the ß1
-helix did not move. In the solvent-accessible areas of the p8 side chains of the p8variants, there was no relationship between the agonists and the antagonists (Figure 4
).
|
|
We also investigated the factors discriminating the null peptides from other ligands (especially antagonist). In the null peptide (p3, p5 and p7) complexes, the calculated deviations for C traces from the index complex in the TCR-binding regions were relatively larger than those of the agonist complexes (Figure 6
). The r.m.s. deviations of the p3null peptide complexes were comparable to those of the p3antagonist complexes (Figures 3A and 6A
). There were no differences in the r.m.s. deviations in the TCR-binding regions between the p3null peptide and the p3antagonist complexes. In the p3null peptide complexes, the p3 side chains were more exposed to solvent than in the p3antagonist complexes (Figure 4
). In the p5null peptide complexes, the r.m.s. deviations were comparable to those of the p5-Gly (an agonist) (Figure 6B
). In the p5null peptides, a smaller range of C
deviations was observed throughout the simulation than in the p3 and p7null peptide complexes (Figure 6
). In the p5variant complexes, a correlation between the solvent-accessible areas of the p5 side chains and the groups of the analogue peptide was not found (Figure 4
). In the p7null peptide variants, the r.m.s. deviations from the index complex in the TCR-binding regions were lower than those of the p7weak antagonist complexes (Figures 3D and 6C
). In the p7Ile and p7Met complexes, the
61,
62 and ß63ß73 region, situated at the center in the groove, shifted. The surface-exposed areas of the p7 side chain were relatively larger than those of the index, agonist and antagonist complexes (Figure 4
).
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
About two thirds of the total energy for the TCRligand (peptideMHC) interaction is directed toward the MHC (Manning et al., 1998). Our simulations, together with our previous study, showed that the r.m.s. deviations of the weak antagonists were relatively larger than those of the strong antagonists at each position (Figure 3
). We see that the weak antagonistic peptides could cause larger structural changes in the TCR-binding sites on HLA molecule than do the strong antagonistic peptides. Thus, these subtle changes of the TCR-binding regions on HLA molecule would reduce affinity for TCR. The affinity (Kd) of the antagonist peptide complexes for the TCR was lower than that of the agonist peptide complexes (Alam et al., 1996
). This would result in a reduction in the time that TCR remain engaged with its ligand (Matsui et al., 1994
). A shorter interaction time between the TCR and its ligand then results in a qualitatively different signal through the TCR (McKeithan, 1995
; Lyons et al., 1996
; Rabinowitz et al., 1996
). Thus, the magnitude of the conformational changes of the HLA scaffold would be relevant to the strength of the TCR antagonism.
The effects of the antagonists on the conformational changes are different among the variants at each peptide position. In the p3variants, peptides with more exposed side chain at p3 tended to be the weak antagonists except the p3Leu (Figure 4). These data suggest that the p3antagonists are distinguished by both the structural changes on the TCR-binding region and the exposed p3 side chain. The TCR could not recognize directly the p4 and p6 side chains which are buried in a pocket as a second anchor residue. The simulations of the p4 and p6variants indicate that changes of the anchor residues have potential to cause the structural alterations of the TCR-recognition surface on the HLA molecule. While the changes at p4 situated under the ß1
-helix induced the ß1
-helix, those at p6 situated under the
1
-helix induced the
1
-helix. Substitutions of p7 induce shifts of both the
1 and the ß1
-helix (Figure 5
) and have a greater potential to cause the structural changes of the TCR-binding sites than those at p3, p4, p5, p6 and p8 (Figures 3 and 6
). In the p8variants, no correlation between the solvent-accessible areas of the p8 side chains and the types of the analogue peptides is found (Figure 4
). No p8variants are classified in the null peptides (Table I
). Therefore, although the p8 side chain projects into solvent like the p5 side chain, the side chain at p8 could not be recognized directly by the TCR. A smaller range of C
deviations was observed throughout the simulation than the other variant complexes (Figure 3
). The r.m.s. fluctuations of the p8variant complexes were hardly affected by substitutions at p8 (data not shown). These data indicated that the p8variants are distinguished through the structural changes at the TCR-binding sites.
We also analyzed the structural features of the null peptide complexes. The r.m.s. deviations of the p3null peptide complexes were comparable to those of the p3antagonists (Figures 3 and 6). It was difficult to explain from the r.m.s. deviations in the TCR-binding regions the differences between the null peptides and the antagonists. The p3 side chains of the p3null peptides were more exposed to solvent than the p3antagonists (Figure 4
). The p3null peptides would be discriminated by changes of the surfaces on the bound peptide components, rather than the conformational change of the TCR-binding surfaces on the HLA molecule. The simulations showed that the r.m.s. deviations of the p5null peptide complexes were lower than those of the p3 and p7null peptides and comparable to the p5Gly (an agonist) (Figure 6
). These data suggested that the changes at p5 hardly affected the structure of the TCR-binding sites. In our model system, the TCR is very sensitive to minor changes in charge and shape at p5 such as the Glu to Asp exchange (Table I
). The p5 side chain projects completely into solvent at the center of the peptide-binding groove. These results indicate that the p5null peptides would be recognized by TCR as completely different ligands mainly through the change of the exposed p5 side chain in the bound peptide. The simulations of the p7null peptide complexes showed that the r.m.s. deviations were smaller than those of the p7weak antagonists (Figures 3 and 6
), suggesting that the structural changes of the TCR-binding sites are not the main factor to be null ligands with regard to p7. The r.m.s. deviations of the p7Trp and p7Tyr complexes were comparable to those of the p7agonists (Figure 6
). The large p7Trp and p7Tyr side chains were not able to fit into shallow pocket 7 and were exposed (Figure 4
). Thus, the p7Trp and p7Tyr complexes were discriminated by the exposed p7 side chains. The p7Ile and p7Met side chains were partly buried, but induced the shifts at the center of the peptide-binding groove unlike the p7antagonists. Thus, the bulky p7 side chain, which is partly buried, affects the center surface of the HLApeptide complex. The p7null peptides would be discriminated by changes of the surfaces on peptideHLA complexes, especially the center of the peptide-binding groove.
Our previous simulations showed that the TCR antagonists could cause larger structural changes in TCR contact regions on the HLA molecule than do the agonists (Toh et al., 1998). In addition, the present MD simulations show that the weak antagonists could induce relatively larger structural changes in TCR-binding regions than do the strong antagonists. Thus, the magnitude of the structural changes of the TCR-binding regions would determine the strength of T-cell antagonism. The simulations also indicate that the changes of the exposed side chain in the bound peptide are the factors in treating the null peptides as completely different ligands. Subtypes of HLADR4 are strongly associated with autoimmune diseases including rheumatoid arthritis (Todd et al., 1988
). Our observations may be useful for targeted vaccine design or immunotherapy with analogue peptides.
![]() |
Notes |
---|
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Andersen,H.C. (1983) J. Comput. Phys., 52, 2434.[ISI]
Berendesen,H.J.C., Grigera,J.R. and Straatsma,T.P. (1987) J. Phys. Chem., 91, 62696271.[ISI]
Bjorkman,P.J. (1997) Cell, 89, 167170.[ISI][Medline]
Chang,H.-C., Smolyar,A., Spoerl,R., Witte,T., Yao,Y., Goyarts,E.C., Nathenson,S.G. and Reinherz,E.L. (1997) J. Mol. Biol., 271, 278293.[ISI][Medline]
Chen,Y.-Z., Mastushita,S. and Nishimura,Y. (1996) J. Immunol., 157, 37833790.[Abstract]
Connolly,M.L. (1983) Science, 221, 709713.[ISI][Medline]
De Magistris,M.T., Alexander,J., Coggeshall,M., Altman,A., Gaeta,F.C., Grey,H.M. and Sette,A. (1992) Cell, 68, 625634.[ISI][Medline]
Dessen,A., Lawrence,C.M., Cupo,S., Zaller,D.M. and Wiley,D.C. (1997) Immunity, 7, 473481.[ISI][Medline]
Ding,H.-Q., Karasawa,N. and Goddard,W.A.,III (1992) J. Chem. Phys., 97, 43094315.[ISI]
Ding,Y.-H., Smith,K.J., Garboczi,D.N., Utz,U., Biddison,W.E. and Wiley,D.C. (1998) Immunity, 8, 403411.[ISI][Medline]
Ding,Y.-H., Baker,B.M., Garboczi,D.N., Biddison,W.E. and Wiley,D.C. (1999) Immunity, 11, 4556.[ISI][Medline]
Dittel,B.N., Sant'Angelo,D.B. and Janeway,C.A.,Jr (1997) J. Immunol., 158, 40654073.[Abstract]
Fremont,D.H., Henderrickson,W.A., Marrack,P. and Kappler,J. (1996) Science, 272, 10011004.[Abstract]
Garboczi,D.N., Ghosh,P., Utz,U., Fan,Q.R., Biddison,W.E. and Wiley,D.C. (1996) Nature, 384, 134141.[ISI][Medline]
Garcia,K.C., Degano,M., Stanfield,R.L., Brunmark,A., Jackson,M.R., Peterson,P.A., Teyton,L. and Wilson,I.A. (1996) Science, 274, 209219.
Garcia,K.C., Degano,M., Pease,L.R., Huang,M., Peterson,P.A., Teyton,L. and Wilson,I.A. (1998) Science, 279, 11661172.
Ghosh,P., Amaya,M., Mellins,E. and Wiley,D.C. (1995) Nature, 378, 457462.[ISI][Medline]
Hadida,F., Haas,G., Zimmermann,N., Hosmalin,A., Spohn,R., Samri,A., Jung,G., Debre,P. and Autran,B. (1995) J. Immunol., 154, 41744186.
Hermans,J., Berendsen,H.J.C. and Postma,J.P.M. (1984) Biopolymers, 23, 15131518.[ISI]
Ikegawa,S., Matsushita,S., Chen,Y.-Z., Ishikawa,T. and Nishimura,Y. (1996) J. Allergy Clin. Immunol., 97, 5364.[Medline]
Jardetzky,T.S., Brown,J.H., Gorga,J.C., Stern,L.J., Urban,R.G., Strominger,J.L. and Wiley,D.C. (1996) Proc. Natl Acad. Sci. USA, 93, 734738.
Jorgensen,J., Esser,U., Fazekas de St. Groth,B., Reay,P.A. and Davis,M.M. (1992) Nature, 355, 224230.[ISI][Medline]
Kersh,G.J. and Allen,P.M. (1996a) Nature, 380, 495498.[ISI][Medline]
Kersh,G.J. and Allen,P.M. (1996b) J. Exp. Med., 184, 12591268.[Abstract]
Kinouchi,R., Kobayashi,H., Sato,K., Kimura,S. and Katagiri,M. (1994) Immunogenetics, 40, 376378.[ISI][Medline]
Kraulis,P.J. (1991) J. Appl. Crystallogr., 24, 946950.[ISI]
Krebs,S., Lamas,J.R., Poenaru,S., Folkers,G., Lopez de Castro,J.A. and Rognan,D. (1998) J. Biol. Chem., 273, 1907219079.
Lim,J.S., Kim,S., Lee,H.G., Lee,K.Y., Kwon,T.J. and Kim,K. (1996) Mol. Immunol., 33, 221230.[ISI][Medline]
Lyons,D.S., Lieberman,S.A., Hampl,J., Boniface,J.J., Chien,Y.-h., Berg,L.J. and Davis,M.M. (1996) Immunity, 5, 5361.[ISI][Medline]
Manning,T.C., Schlueter,C.J., Brodnicki,T.C., Parke,E.A., Speir,J.A., Garcia,K.C., Teyton,L., Wilson,I.A. and Kranz,D.M. (1998) Immunity, 8, 413425.[ISI][Medline]
Mathiowetz,A.M., Jain,A., Karasawa,N. and Goddard,W.A.,III (1994) Proteins: Struct. Funct. Genet., 20, 227247.[ISI][Medline]
Matsui,K., Boniface,J.J., Steffner,P., Reay,P.A. and Davis,M.M. (1994) Proc. Natl Acad. Sci. USA, 91, 1286212866.
Matsuoka,T., Kohrogi,H., Ando,M., Nishimura,Y. and Matsushita,S. (1996) J. Immunol., 157, 48374843.[Abstract]
Matsushita,S., Takahashi,K., Motoki,M., Komiyama,K., Ikagawa,S. and Nishimura,Y. (1994) J. Exp. Med., 180, 873883.[Abstract]
McKeithan,T.W. (1995) Proc. Natl Acad. Sci. USA, 92, 50425046.[Abstract]
Meng,W.S., Grafensen,H. and Haworth,I.S. (1997) Int. Immunol., 9, 13391346.[Abstract]
Murthy,V.L. and Stern,L.J. (1997) Structure, 5, 13851396.[ISI][Medline]
Rabinowitz,J.D., Beeson,C., Lyons,D.S., Davis,M.M. and McConnell,H.M. (1996) Proc. Natl Acad. Sci. USA, 93, 14011405.
Reid,S.W. et al. (1996) J. Exp. Med., 184, 22702286.
Rognan,D., Reddehase,M.J., Koszinowski,U.H. and Folkers,G. (1992a) Proteins: Struct. Funct. Genet., 13, 7085.[ISI][Medline]
Rognan,D., Zimmermann,N., Jung,G. and Folkers,G. (1992b) Eur. J. Biochem., 208, 101113.[Abstract]
Rognan,D., Scapozza,L., Folkers,G. and Daser,A. (1994) Biochemistry, 33, 1147611485.[ISI][Medline]
Rognan,D., Scapozza,L., Folkers,G. and Daser,A. (1995) Proc. Natl Acad. Sci. USA, 92, 753757.[Abstract]
Rognan,D., Krebs,S., Kuonen,O., Lamas,J.R., Lopez de Castro,J.A. and Folkers,G. (1997) J. Comput.-Aided Mol. Des., 11, 463478.
Sant'Angelo,D.B., Waterbury,G., Preston-Hurlburt,P., Voon,S.T., Medzhitov,R., Hong,S.-C. and Janeway,C.A.,Jr (1996) Immunity, 4, 367376.[ISI][Medline]
Scott,C.A., Peterson,P.A., Teyron,L. and Wilson,I.A. (1998) Immunity, 8, 319329.[ISI][Medline]
Sloan-Lancaster,J., Evavold,B.D. and Allen,P.M. (1993) Nature, 363, 156159.[ISI][Medline]
Smith,K.D. and Lutz,C.T. (1997) J. Immunol., 158, 28052812.[Abstract]
Smith,K.J., Pyrdol,J., Gauthier,L., Wiley,D.C. and Wucherpfenning,K.W. (1998) J. Exp. Med., 188, 15111520.
Steele,J.C., Young,S.P., Goodall,J.C. and Gallimore,P.H. (1998) J. Immunol., 161, 47454752.
Stern,L.J., Brown,J.H., Jardetzky,T.S., Gorga,J.C., Urban,R.G., Stominger,J.L. and Wiley,D.C. (1994) Nature, 368, 215221.[ISI][Medline]
Sugita,Y and Kitao,A. (1998) Proteins: Struct. Funct. Genet., 30, 388400.[Medline]
Swope,W.C. and Anderson,H.C. (1982) J. Chem. Phys., 76, 637649.[ISI]
Tana,T., Kamikawaji,N., Savoie,C.J., Sudo,T., Kinoshita,Y. and Sasazuki,T. (1998) J. Hum. Genet., 43, 1421.[ISI][Medline]
Teng,M.-K., Smolyar,A., Tse,A.G.D., Liu,J.-H., Liu,J., Hussey,R.E., Nathenson,S.G., Chang,H.-C., Reinherz,E.L. and Wang,J. (1998) Curr. Biol., 8, 409412.[ISI][Medline]
Todd,J.A. et al. (1988) Science, 240, 10031009.[ISI][Medline]
Toh,H., Kamikawaji,N., Tana,T., Sasazuki,T. and Kuhara,S. (1998) Protein Eng., 11, 10271032.[Abstract]
Received December 2, 1999; revised March 2, 2000; accepted April 7, 2000.