SUNY at Albany
June 19-23, 2001
Characterization of the peptide-receptive form of the human class II major histocompatibility complex HLA-DR1.
Major histocompatibility complex (MHC) proteins are cell-surface glycoproteins that bind short peptides antigens and present them at the cell surface for recognition by CD4+ T-cell receptors. A distinct difference in conformation exists between empty and peptide-loaded forms of the human class II major histocompatibility complex HLA-DR1. Kinetics studies have indicated that the empty protein exists in two conformations in equilibrium: one peptide receptive and one unable to bind peptide. A mixture of these two conformations was previously used to characterize the difference between empty and peptide-loaded HLA-DR1. Dynamic light scattering experiments showed that the hydrodynamic radius for peptide-loaded DR1 is ~5? smaller than that for the empty protein; this was further confirmed by a sedimentation velocity analysis in which the calculated sedimentation coefficient for the empty DR1 was 37.4?, significantly larger than that for the peptide-loaded, 31.8?. Using a variety of biophysical methods including gel filtration, circular dichroism, and ELISA, we have been trying to characterize differences between the peptide receptive and the inactive empty forms of HLA-DR1. While a significant change in conformation is readily observed between the peptide-loaded and the mixture of empty forms of the protein using these methods, we have not observed differences between the peptide receptive and inactive forms. Thus, the conformational changes responsible for inactivation are smaller and distinct from those that occur concomitant with peptide binding.
Zarixia Zavala-Ruiz, Jennifer Zarutskie, and Lawrence J. Stern.
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.