Thursday, November 13, 2008, Condensed Matter Biological Physics Seminar, Prof. Christian Salesse, Université Laval, Quebec City, Canada, "Preferential Binding, Organization and Structure of Membrane-Associated Proteins onto Monolayers at the Air-Water Interface", 4:30 PM, Doherty Hall A310, CMU

Abstract

A large number of proteins are associated with membranes either through an alpha helical transmembrane segment or an acyl group. The parameters responsible for the modulation of the membrane binding of such proteins are largely unknown. We have measured the binding of a myristoylated protein (recoverin) whose conformation is calcium dependent (see figure below), as well as a farsenylated protein (phosphodiesterase 6, PDE6), a non acylated protein (retinitis pigmentosa 2, RP2), and a protein bearing an alpha helical transmembrane segment (retinol dehydrogenase 11, RDH11) onto lipid monolayers at the air-water interface. The rate of monolayer binding of myristoylated recoverin is highly enhanced compared to non myristoylated recoverin. Moreover, the rate of monolayer binding of the full RDH11 bearing a transmembrane alpha helical segment is much larger than that of the truncated RDH11 which contains no transmembrane segment. However, the extent of binding of the truncated RDH11 is larger than the full RDH11 which suggests that other components of this protein contribute to membrane binding in addition to the transmembrane alpha helical segment. Moreover, myristoylated recoverin and RDH11 show a preferential binding onto polyunsaturated phospholipid monolayers whereas PDE and RP2 preferentially bind saturated phospholipids which suggests that they could be located to membrane rafts. In addition, we have performed measurements of infrared spectra of these monolayers using polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The data show that monolayer binding of myristoylated recoverin is highly stable compared to non myristoylated recoverin which denatures as a function of time. Moreover, the PM-IRRAS spectrum of myristoylated recoverin has been simulated on the basis of its known structure which allowed to determine its orientation with respect to the plane of the monolayer. In addition, the PM-IRRAS spectra of RP2 demonstrate that its structure and orientation are very different in the presence and absence of a lipid monolayer and that its orientation changes with monolayer surface pressure whereas the structure of RDH11 remains unchanged in the presence and absence of a lipid monolayer.