Cell surface clusters of MHC class I molecules

Applicant FWF: Dr. Peter Lanzerstorfer, Faculty of Engineering, University of Applied Sciences Upper Austria, Austria. Applicant DFG: Univ. Prof. Dr. Sebastian Springer, Department of Life Sciences and Chemistry, Jacobs University Bremen, Germany. MHC-class I-proteins (MHC-proteins) can be found on the surface of almost all cell types and are mainly responsible for antigen presentation for cytotoxic T cells (T-killer cells). Infected and degenerated cells that produce foreign proteins can thus be specifically identified by the T-killer cells and subsequently eliminated. MHC-proteins are therefore essential for cellular immunity against viruses, intracellular bacteria, and tumours. The cell surface form of the MHC-protein, which binds the T cell receptor, is a non-covalent protein complex consisting of three subunits (trimer): the heavy chain (HC) anchored to the cell membrane, the smaller soluble subunit beta-2-microglobulin (ß2 m) and an antigenic peptide. Under physiological conditions, the peptide presented on the cell surface dissociates from the trimer after a few hours to days (depending on affinity) and an `empty dimer` of HC and ß2 m remains. From this dimer, ß2 m dissociates within a few minutes, and the "free" HC (FHC) remains. We have recently shown that FHCs assemble into clusters on the cell surface. These clusters consist of several FHCs that interact in cis (on the same membrane). Cluster formation has been demonstrated for the first time using a `two-hybrid` antibody-micropattern assay. Our preliminary data suggest that the a3 -domain of the FHC is sufficient for interaction. Furthermore, it appears that FHC clusters are of transient nature, mainly consisting of protein dimers and are responsible for efficient endocytosis of MHC-proteins. Furthermore, possible functions in the transmission of stress signals to other cells of the immune system have been discussed but not yet proven. In the present project, the following points should be clarified: i) Which MHC-allotypes are subject to FHC cluster formation?, ii) How are FHC clusters formed spatially and what are their dynamics?, and iii) What is the biological and physiological function of those clusters? Different methodological approaches will be applied to answer these questions. In order to detect FHC clusters and to get first insights into the interaction dynamics, an adapted antibody-micropattern assay is used. The spatial elucidation of the potential clusters is achieved by means of in-silico models and X-ray crystallography. Single-molecule spectroscopy will provide detailed information about the size, dynamics and affinity of the clusters. Thus, the project lays the basis for a systematic investigation of the physiological role of peptide-free MHC-class I-molecules on the cell surface.

No additional funding sources recorded.