Comparative biophysical characterization of chicken β2-microglobulin Original Research Article

β2-microglobulin (β2m) is the smallest building block of molecules belonging to the immunoglobulin superfamily. By comparing thermodynamic and structural characteristics of chicken β2m with those of other species, we seek to elucidate whether it is possible to pinpoint features that set the avian protein apart from other β2m. The thermodynamic assays revealed that chicken β2m exhibits a lower melting temperature than human β2m, and the H/D exchange behavior observed by infrared spectroscopy indicates a more flexible structure of the former protein. To understand these differences at a molecular level, we determined the structure of free chicken β2m by X-ray crystallography to a resolution of 2.0 Å. Our comparisons indicate that certain biophysical characteristics of the chicken protein, particularly its conformational flexibility, diverge considerably from those of the other β2m analyzed, although basic structural features have been retained through evolution.