The biophysical principles of membrane insertion and folding of integral membrane proteins are not well understood. To investigate these principles, we will develop a lipid-bilayer based in vitro refolding system for a recently discovered outer membrane protein G (OmpG) of E. coli. We will investigate structure formation on OmpG by fluorescence-, circular dichroism- and electron spin resonance- spectroscopy, stopped-flow methods, and also by electrophoresis. OmpG forms a (monomeric) pore with a diameter of ca. 2.5 nm (Behlau et al., 2001), indicating that OmpG is a 14-standed ß-barrel. The folding of OmpG (i.e. the kinetic phases, activation energies, and folding intermediates) from a urea-denatured state will be compared to our results on the refolding of OmpA, an 8-stranded ß-barrel. Enthalpic and entropic contributions to the free energy unfolding of OmpG will be determined. The impact of recently discovered periplasmic chaperones and isomerases (PpiA, PpiD, FkpA, etc. of E. coli) on the folding kinetics and folding yields of OmpG will be investigated using site-directed fluorescence labeling and site-directed spin-labeling. Finally, through our research on the mechanism of membrane protein folding, we aim to develop more generally applicable, biotechnologically important strategies to refold transmembrane proteins with high yields.