Assembly of MHC class II molecules: A structural investigation of protein-protein and protein-lipid interactions within the lipid bilayer
Final Report Abstract
The goal of this joined research project has been to study roles of transmembrane domains and proteinlipid cofactor interactions in trafficking and function of the MHC class II heterodimer of DQA1 and DQB1. While some information on structures of the transmembrane domains have been obtained by NMR and biochemical studies, technical problems caused some significant delays, thus, some of the proposed studies are still in progress. In the course of the project, we unexpectedly discovered that CD74, which oligomerises with DQA1 and DQB1 during trafficking of the heterodimer, is a heme binding protein, and that the mode of heme coordination switches during its proteolytical trimming. Structural similarities of different SPPL2a/b substrates suggested that heme binding is not a unique feature of CD74 but rather a common characteristic of proteins undergoing SPPL2a/b mediated regulated intramembrane hydrolysis. In addition to CD74 we tested five members of this protein family and found all of them to bind heme. Our data suggest that heme binding switches during processing from a high to low affinity heme binding mode. We are currently testing the hypothesis that heme cofactor binding of CD74 contributes to the ascribed function as transcription factors of its liberated ICD. In summary, our identification of modulated cofactor binding of transmembrane signalling proteins by regulated intramembrane proteolysis sheds new light on the regulation of cell signalling pathways. It is tempting to speculate that lipid binding either to MHC class II or CD74 itself contributes to modulation of proteolytical processing of CD74 and other members of the family. With the tools and methods established in this joined grant, we are now in a position to address these questions in future experiments.
Publications
- Bifunctional Sphingosine for Cell-Based Analysis of Protein-Sphingolipid Interactions. ACS Chem Biol, 2016;11(1):222-30
Haberkant P, Stein F, Höglinger D, Gerl MJ, Brügger B, Van Veldhoven PP, Krijgsveld J, Gavin AC, Schultz C
(See online at https://doi.org/10.1021/acschembio.5b00810) - Sphingosine-1-phosphate lyase deficient cells as a tool to study protein lipid interactions. PlosOne, 2016;11(4):e0153009
Gerl MJ, Bittl V, Kirchner K, Sachsenheimer T, Brunner HL, Lüchtenborg C, Özbalci C, Wiedemann H, Wegehingel S, Nickel W, Haberkant P, Schultz C, Krüger M and Brügger B
(See online at https://doi.org/10.1371/journal.pone.0153009) - CerS6-Derived Sphingolipids Interact with Mff and Promote Mitochondrial Fragmentation in Obesity. Cell 2019 May 30; 177 (6): 1536-1552
Hammerschmidt P, Ostkotte D, Nolte H, Gerl, MJ, Jais A, Brunner HL, Sprenger HG, Awazawa M, Nicholls HT, Turpin-Nolan SM, Langer T, Krüger M, Brügger B, Brüning JC
(See online at https://doi.org/10.1016/j.cell.2019.05.008)
