"Type II secretion in Gram-negative bacteria is the general exit route for proteins that function outside the cell. During secretion, preproteins are first translocated across the inner membrane, after which the dedicated type II secretion system transports the protein across the outer membrane. In Klebsiella oxytoca the outer membrane pore is formed upon dodecamerisation of PulD, a founder member of the secretin superfamily. The minimal assembly unit of PulD, comprising the transmembrane C-domain preceded by part of the periplasmic N-domain and a short PulS-interaction domain at its C-terminus, assembles spontaneously with high efficiency in vitro in liposomes. The current proposal is aimed at elucidating the folding and assembly mechanism of the minimal PulD dodecamer in vitro. Using a combined approach of mutagenesis and variation of the lipid membrane environment it aims to isolate folding intermediate states along the pathway to the native state. Each intermediate will be characterised structurally by applying a wide range of biophysical and biochemical techniques. Together, these efforts will contribute to our understanding of how sequence determines structure in membrane proteins in the context of a lipid bilayer and at expanding the emerging field of membrane protein folding into more complex systems."
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