Expression levels of MHC class I molecules are inversely correlated with promiscuity of peptide binding.

Funding Wellcome Trust (Programme grant 089305) El Kahina Meziane Michael Harrison Łukasz Magiera Clemens Hermann Laura Mears Antoni G Wrobel Charlotte Durant Jim Kaufman Biotechnology and Biological Sciences Research Council (BBSRC) (Core Funding to the Pirbright Institute) William Mwangi Colin Butter Venugopal Nair Biotechnology and Biological Sciences Research Council (BBSRC) (PhD studentship) Paul E Chappell Wellcome Trust (Senior Investigator Award) Susan M Lea The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication. Acknowledgements We thank many colleagues at the IAH (now rebranded as the Pirbright Institute) for much historical help in processing materials for analysis of MHC-bound peptides, especially Larry Hunt from the Protein Chemistry facility for analysis of eluted peptides by Edman degradation and for provision of synthetic peptides. We thank Diamond Light Source for access to beamlines I02, I03, I04, and I04-1 (mx9306) that contributed to the results presented here. The B14 structural experiments were performed on the ID29 beamline at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. We are grateful to Local Contact at ESRF for providing assistance in using beamline ID29. We also thank Ed Lowe from the Biochemistry Department, Oxford for data collection and members of the Lea lab for crystallography discussions. We thank Steve Marsh from the Anthony Nolan, Tom Pizzari from Oxford Zoology, and Lars Råberg from Lund University for helpful discussions. We thank Gillian Griffiths, Alison Schuldt, Michaela Fakiola, and Mike Ratcliffe for critical reading of the manuscript. The authors declare no conflicts of interest.