Cell surface expression of hybrid murine/human MHC class II beta alpha dimers. Key influence of residues in the amino-terminal portion of the beta 1 domain.
To aid in the identification of key residues responsible for the control of class II MHC beta-alpha dimer assembly and expression, a series of cotransfections of human plus mouse beta- and alpha-genes was performed. The resulting expression data were correlated with the sequences of the relevant proteins to identify residues that played critical roles in these processes. For the I-E/DR homologues good expression was seen for both E beta DR alpha and DR beta E alpha combinations involving several allelically variable beta-chains of each species. These results are consistent with the sequence conservation seen for I-E and DR gene products, and indicate that the species-specific differences that do exist play little role in controlling dimer formation or transport. For A beta chains, a more complex picture was seen. A beta d, but not A beta k or A beta b, was found to coexpress with human alpha-chains. Not only did A beta d show expression with the homologous DQ alpha-chain, but it also was expressed with DR alpha and DP alpha. These data indicate that species-specific residues do not control dimer expression under these conditions and confirm that allelically polymorphic residues have a crucial role in this process. Mapping studies using recombinant A beta genes established the importance of the residues in the amino-terminal half of the beta 1 domain in the differences observed among the A beta alleles. Sequence comparison of DR beta, DP beta, DQ beta, E beta, and A beta chains in this region revealed a single residue (position 12) conserved in most chains and differing in a nonconservative fashion between A beta d vs A beta b or k. A beta d has the conserved lysine at this position, whereas A beta b has methionine and A beta k has glutamine. To test whether this residue actually was important physiologically, a lysine codon was created in a recombinant A beta gene possessing the amino-terminal sequence of the kappa haplotype, and the ability of this mutant chain to be expressed with various mouse A alpha-chains was examined. This mutant chain was shown to gain the ability to be efficiently expressed with A alpha d without losing its ability to be expressed with A alpha k. These data reemphasize the special role played by allelically polymorphic residues in Ia expression and identify one such polymorphic site as position 12.(ABSTRACT TRUNCATED AT 400 WORDS)
Department of Immunology, Royal Postgraduate Medical School, Hammersmith Hospital, London, England.
R I
RI
Lechler
A J
AJ
Sant
N S
NS
Braunstein
R
R
Sekaly
E
E
Long
R N
RN
Germain
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004252:DNA Mutational Analysis; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007158:Immunologic Techniques; D007739:L Cells; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship; D014162:Transfection
D000949:Histocompatibility Antigens Class II; D046911:Macromolecular Substances; D011994:Recombinant Proteins