The Previously Defined Rd Class I Molecule is a Non-ß2M Associated Conformational Variant of Ld
Post-translational differences between murine class I molecules were compared. As determined in a pulse-chase experiment, the rate of N-linked oligosaccharide processing of Ld molecules was found to be 4–5 times slower than that of Dd, Kd or Ddml molecules. Furthermore, the relative molar ratio of ß2m to class I was found to be significantly lower with Ld than with Dd, Kd or Ddml molecules. Thus, both the slower processing and weaker ß2m association correlate with the previously reported lower cell surface expression of Ld compared to Dd, Kd or Ddml molecules. Since Ddml is a chimeric Dd/Ld molecule these results demonstrate that the amino terminus of the class I molecule influences processing, ß2m-association and cell surface expression.
The Rd molecule was initially defined by sequential immunoprecipitation using anti-Ld reactive mAbs 30–5–7 (α2 specific) and 28–14–8 (α3 specific). In contrast to Ld, the Rd molecule is only positive with mAb 28–14–8. In this communication we demonstrate that both Ld and Rd are products of the H-2L d gene using an H-2L d gene transfectant. Furthermore, the 30–5–7- Ld molecule (Rd) was found not to be ß2m associated, in contrast to the 30–5–7+ Ld molecule where ß2m was readily apparent. As much as 40% of the biosynthetically-labelled Ld molecules were found in this non-ß2m associated conformation. Thus, these studies suggest that Ld molecules have several unique properties that could all be related to an aberrant ß2m association. These properties include slower oligosaccharide processing, lower cell surface expression and detection of a non-ß2m associated conformational variant.
KeywordsCell Surface Expression Sequential Precipitation Antigen Preparation Daudi Cell Complex Type Oligosaccharide
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