Allotype-specific dynamics revealed in peptide-receptive Major Histocompatibility Complex class I molecules

Van Hateren, Andrew (2017) Allotype-specific dynamics revealed in peptide-receptive Major Histocompatibility Complex class I molecules. 9th International Workshop on MHC Antigen Processing and Presentation, , Salamanca, Spain. 28 - 31 May 2017.

Record type: Conference or Workshop Item (Poster)

Abstract

Major Histocompatibility Complex class I molecules (MHC I) bind and present peptides to cytotoxic T lymphocytes. MHC I molecules select peptides for presentation from a large diversity in the endoplasmic reticulum. However, few peptides bind with high affinity, which is necessary for efficient antigen presentation to ensue.

MHC I molecules have an intrinsic ability to discriminate between peptides, but the efficiency varies between allotypes, and the peptide selection mechanism is unknown. Indirect evidence suggests MHC I molecules transiently adopt higher energy conformations than the native peptide-MHC I structures observed by x-ray crystallography, but experimental observations have been hindered by the instability of peptide-empty MHC I.

Here, we sought to characterise the dynamic nature of MHC I by refolding with UV labile conditional peptide ligands, and comparing the hydrogen-deuterium exchange (HDX) profiles of peptide-loaded MHC I with peptide-receptive MHC I created following UV induced peptide lysis.

HDX provides direct observations of changes in the dynamics of proteins on the seconds, minutes and hour time scales, which are not accessible to X-ray crystallographic or in silico studies, and HDX may therefore offer unique perspective of MHC I peptide selection.

We found:
Differences in the HDX profiles of peptide-loaded and peptide-receptive MHC I molecules.
These changes were reversed by the addition of peptide, confirming UV exposed MHC I molecules were receptive to binding peptide.
The largest increases in deuterium uptake occurred in the peptide-binding domain after UV induced lysis of the conditional ligand.
However, increases were also observed in the α3 and β2-microglobulin domains, demonstrating allosteric “domain-domain” communication throughout MHC I.

We also compared the HDX profiles of two MHC I allotypes which differ in their intrinsic ability to select peptides.
While both MHC I allotypes shared a similar overall pattern of increased HDX after UV exposure, there were allotype-specific differences in the magnitude of the changes.
Specifically there was greater deuterium uptake in the allotype with the greatest intrinsic ability to select peptides, consistent with the notion that peptide selection is related to the plasticity of MHC I molecules.

In conclusion, we have observed both peptide dependent and allotype dependent differences in the HDX profiles of MHC I molecules, demonstrating the dynamic properties of MHC I molecules in the peptide loaded and peptide receptive states.

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