High impact information on Qdm

• Recognition of the class Ib antigen Qa-1 by a portion of alloreactive cytotoxic T lymphocyte (CTL) clones requires that the target cell express a second gene, termed Qa-1 determinant modifier (Qdm) [1].
• The Qa-1(b) peptide-binding site is predominantly occupied by a single nonameric peptide, Qa-1 determinant modifier (Qdm), derived from the leader sequence of H-2D and L molecules [2].
• Our findings suggest that it may be difficult for viruses to generate decoy peptides that mimic Qdm and raise the possibility that competitive replacement of Qdm with other peptides may provide a novel mechanism for activation of NK cells [2].
• Qdm is the dominant peptide loaded onto Qa-1 under physiological conditions and this peptide has an optimal sequence for binding to Qa-1 [3].
• Tapasin was also required for the presentation of endogenous Qdm peptides to Qdm-specific, Qa-1b-restricted CTLs [4].

Biological context of Qdm

• The Qdm+ allele regulated in trans Qa-1 epitope expression from a Qdmk chromosome, modifying expression of particular CTL-defined Qa-1 antigenic determinants rather than affecting levels of cell surface expression [5].
• H-2Dk homozygous haplotypes expressed a recessive allele of the modifier, Qdmk, whereas all other H-2 haplotypes tested expressed a dominant allele, Qdm+ [5].
• Mechanisms of Qdm function may include either a novel protein modification system or an unprecedented case of antigen recognition restricted by a nonclassical major histocompatibility complex molecule [5].
• One of the Pema class I cDNA clones classified as H2-K, D/L-like (class I a) is predicted to encode an identical peptide, implying that an antigen binding protein (Qa1) and the antigen to which it binds (the product of Qdm) has been conserved for over 50 My [6].

Anatomical context of Qdm

• Alloreactive anti-Qa-1 T cells can be assigned into three different specificity groups based on a Qa-1 modifying gene, Qdm, as well as Qa-1 epitope expression on Tap-2-deficient RMA-S cells [7].
• Third, the expression of Qa-1b on lymphoblasts is approximately 1 to 1.25 x 10(4) molecules/cell indicating that the Qdm peptide must be derived from both cell membrane and intracellular compartments [8].

Associations of Qdm with chemical compounds

• However, changing the Arg at P7 of the DL to a Cys can alter its trafficking and allows for TAP-independent presentation of the Qdm epitope [9].

Physical interactions of Qdm

• The Qa-1/Qdm complex is the primary ligand for CD94/NKG2A inhibitory receptors expressed on a major fraction of natural killer (NK) cells [10].

Other interactions of Qdm

• Regulation of Qa-1 expression and determinant modification by an H-2D-linked gene, Qdm [5].
• However, at the cell surface the hybrid molecules were stably associated with beta 2-microglobulin and were recognized by cytotoxic T lymphocyte (CTL) clones specific for the Qa-1b-presented peptide Qdm (AMAPRTLLL) [11].

Analytical, diagnostic and therapeutic context of Qdm

• A candidate peptide-binding motif was determined by sequence analysis of peptides eluted from Qa-1 that had been folded in the presence of random peptide libraries or pools of Qdm derivatives randomized at specific anchor positions [2].

References