Structural basis for helper T-cell and antibody epitope immunodominance in bacteriophage T4 Hsp10. Role of disordered loops.
Antigen three-dimensional structure potentially limits the access of endoproteolytic processing enzymes to cleavage sites and of class II major histocompatibility antigen-presenting proteins to helper T-cell epitopes. Helper T-cell epitopes in bacteriophage T4 Hsp10 have been mapped by restimulation of splenocytes from CBA/J and C57BL/6J mice immunized in conjunction with mutant (R192G) heat-labile enterotoxin from Escherichia coli. Promiscuously immunogenic sequences were associated with unstable loops in the three-dimensional structure of T4 Hsp10. The immunodominant sequence lies on the N-terminal flank of the 22-residue mobile loop, which is sensitive to proteolysis in divergent Hsp10s. Several mobile loop deletions that inhibited proteolysis in vitro caused global changes in the helper T-cell epitope map. A mobile loop deletion that strongly stabilized the protein dramatically reduced the immunogenicity of the flanking immunodominant helper T-cell epitope, although the protein retained good overall immunogenicity. Antisera against the mobile loop deletion variants exhibited increased cross-reactivity, most especially the antisera against the strongly stabilized variant. The results support the hypothesis that unstable loops promote the presentation of flanking epitopes and suggest that loop deletion could be a general strategy to increase the breadth and strength of an immune response.
Dai
Guixiang
G
Department of Biochemistry, Tulane University Health Sciences Center, New Orleans, Louisiana 70112-2699, USA.
Carmicle
Stephanie
S
Steede
N Kalaya
NK
Landry
Samuel J
SJ
D000595:Amino Acid Sequence; D000818:Animals; D017122:Bacteriophage T4 / Q000737:chemistry*; D018835:Chaperonin 10 / Q000737:chemistry* / Q000276:immunology*; D018604:Epitope Mapping; D018984:Epitopes, T-Lymphocyte; D005260:Female; D016056:Immunodominant Epitopes; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008969:Molecular Sequence Data; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*
D018835:Chaperonin 10; D018984:Epitopes, T-Lymphocyte; D016056:Immunodominant Epitopes