Biophysics and Soft Matter Seminar
Investigating the Phase Behaviour of Oriented Model Membrane Containing Peptides
Dept of Physics, University of Guelph
July 21, 2016 at 12:00 pm in P8445.2
Biological membranes are complex and dynamic systems that perform critical roles for the cell. In order to gain insight into the pha behaviour and molecular dynamics of membranes, we use simplified models which mimic properties of biological membranes. Mixtures made with two long-chain phospholipid species, one saturated and one unsaturated, along with cholesterol can exhibit coexisting liquid disordered and liquid ordered fluid bilayer phases. The phase behaviour of lipids and peptides in model membranes can be investigated using 2H NMR since 2H quadrupolar splittings are sensitive to molecular motion and orientational order. Static 2H spectra are significantly simpler for oriented samples than for "powder" samples making oriented samples advantageous. Oriented model membranes can be aligned magnetically (bicelles) or mechanically (on glass slides).
The effect of two peptides, Conolysin-Mt1 and ALGA, on the phase behaviour of oriented model membranes was investigated in this work. Conolysin-Mt1, a small, membrane-active peptide found in the venom of a sea snail was studied in standard bicelles. The lipid chain order in bicelles containing Conolysin-Mt1 was affected slightly by the presence of the peptide. ALGA, a short, helical synthetic peptide was studied in both bicelles and bilayers aligned on glass slides. The presence of ALGA disrupted the alignment of the bicelles and changes the phase behaviour of the lipids by raising the temperature at which the liquid ordered phase begins. In addition, there were two populations of ALGA found in the mixtures on glass slides; one in which the molecules undergo rapid axial reorientation, the other which is characteristic of a powder peptide.