Structure of a classical MHC class i molecule that binds Non-Classical ligands

Chicken yf1 genes share a close sequence relationship with classical mhc class i loci but map outside of the core mhc region. to obtain insights into their function,we determined the structure of the yf1*7.1/β2-microgloblin complex by x-ray crystallography at 1.3 å resolution. it exhibits the architecture typical of classical mhc class i molecules but possesses a hydrophobic binding groove that contains a non-peptidic ligand. this finding prompted us to reconstitute yf1*7.1 also with various self-lipids. seven additional yf1*7.1 structures were solved,but only polyethyleneglycol molecules could be modeled into the electron density within the binding groove. however,an assessment of yf1*7.1 by native isoelectric focusing indicated that the molecules were also able to bind nonself-lipids. the ability of yf1*7.1 to interact with hydrophobic ligands is unprecedented among classical mhc class i proteins and might aid the chicken immune system to recognize a diverse ligand repertoire with a minimal number of mhc class i molecules. © 2010 hee et al.