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2 Domain Loop Influences Interaction with the Assembly Complex1



*
Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110;
Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, NE 68198; and
Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843
Presentation of antigenic peptides to CTLs at the cell surface
first requires assembly of MHC class I with peptide and
ß2-microglobulin in the endoplasmic reticulum. This
process involves an assembly complex of several proteins, including
TAP, tapasin, and calreticulin, all of which associate specifically
with the ß2-microglobulin-assembled, open form of the
class I heavy chain. To better comprehend at a molecular level the
regulation of class I assembly, we have assessed the influence of
multiple individual amino acid substitutions in the MHC class I
2
domain on interaction with TAP, tapasin, and calreticulin. In this
report, we present evidence indicating that many residues surrounding
position 134 in H-2Ld influence interaction with assembly
complex components. Most mutations decreased association, but one
(LdK131D) strongly increased it. The Ld
mutants, with the exception of LdK131D, exhibited
characteristics suggesting suboptimal intracellular peptide loading,
similar to the phenotype of Ld expressed in a
tapasin-deficient cell line. Notably, K131D was less peptide inducible
than wild-type Ld, which is consistent with its unusually
strong association with the endoplasmic reticulum assembly
complex.
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