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Molekulare Biophysik Gemeinsames Kolloquium Referent: PD Dr. Dirk Schneider Universität Freiburg Thema: Shaping up membranes and membrane proteins In contrast to other bacteria but similar to chloroplasts, cyanobacteria harbor six internal compartments (thylakoid lumen, thylakoid membrane, cytoplasm, cytoplasmic membrane, periplasm, outer membrane), and all these compartments appear to harbor a defined subset of proteins. It is, however, still unclear how cyanobacteria sort proteins into these specific compartments and, thus, how biogenesis and maintenance of specialized subcellular compartments is organized. How does a cyanobacterial cell "decide" which proteins are translocated into the thylakoid lumen and which proteins are sorted into the periplasmic space? This "sorting problem" is essentially completely unresolved yet. I will present and discuss our recent work on protein sorting and thylakoid membrane biogenesis in cyanobacteria with a special focus on a cyanobacterial chaperone network. In a second part I will talk about folding, assembly and stability of -helical membrane proteins. Many α-helical membrane proteins form complexes within membranes and fulfil important cellular functions by e.g. mediating the transfer of energy, of chemical compounds, or of signals across biological membranes. Unfortunately, the abilities to produce, analyze, and manipulate membrane proteins lag far behind the field of water-soluble proteins. Our primary goal is to gain deeper insights into the functional role of individual factors for folding, assembly, and stabilization of membrane proteins. In doing so, we hope to improve existing tools for characterizing membrane proteins and extend their applicability to larger membrane proteins. We make a critical assessment of the hierarchical or stepwise nature of membrane protein folding implied in the Two-Stage folding model, and we are mainly interested in the contributions of individual amino acids, of amino acid motifs, and of cofactors for folding and assembly of membrane proteins. Our studies entail the assembly of entire membrane proteins themselves, as well as the association of protein fragments, both in vivo and in vitro. In particular, we intend to develop a detailed understanding of the energetic contributions of different amino acid side-chains in helix-helix interactions, as well of the role played by cofactors. Ort: HS 18, Zoologie Johann-Joachim-Becher-Weg 9 Zeit: Montag, 08.12.2008, 17.15 Uhr Info: http://iabserv.biologie.uni-mainz.de/index.php Biologie