30-OR

Abstract

β 2-microglobulin ( β 2m) is a small, monomorphic protein non-covalently bound to the heavy chain (HC) in polymorphic major histocompatibility complex (MHC) class I molecules. Given the high evolutionary conservation of structural features of β 2m in various MHC complexes as shown by X-ray crystallography, β 2m is often considered as a mere scaffolding protein. We investigate here whether β 2m residues at the interface to the HC exhibit changes depending on HC polymorphisms and the peptides bound to the complex in solution. We employ High-Cell-Density Fermentation (HCDF) to obtain deuterated β 2m and Nuclear Magnetic Resonance (NMR) spectroscopy to examine the β 2m-HC interface. Following complexation of β 2m, the HLA-B*27:09 HC, and a peptide, the NMR resonance assignments are used to examine the β 2m-HC interface. We then compare the resonances of β 2m in two minimally distinct subtypes, HLA-B*27:09 and HLA-B*27:05, that are differentially associated with the spondyloarthropathy Ankylosing Spondylitis. Each of these subtypes is complexed with three self-peptides (TIS, pVIPR, pGR) and a viral peptide (pLMP2) for which structural information is already available. The resonance of β 2m-Trp95 does not show any variation in chemical shift, thus serving as an ideal internal control. However, there are distinct resonance signals for β 2m-Trp60 in each of the complexes. As these signals are not only distinguishable for a given HLA-B27 subtype, but are also in characteristic positions within the spectra for each of the four peptides employed here, this indicates the existence of an unexpected plasticity that enables β 2m to accommodate changes depending on HC polymorphism as well as on the bound peptide through subtle structural variations of the protein-protein interface.