Chemical Physics of bio- and model membranes
We are interested in understanding how membrane protein activity is affected by the properties of the hosting lipid bilayer. In particular, the mechanical properties of the lipid bilayer in terms of elastic constants and viscous phenomena play a relevant role. In this context it is extremely important to analyze bilayer mechanical properties on the nanometer scale, the relevant scale for proteins. We study by means of temperature-controlled Atomic Force Microscopy/Spectroscopy the nanomechanical properties of a specific bio-membrane models: supported lipid bilayers (SLBs). SLBs represent a very interesting systems that can be easily assembled on a variety of surfaces. SLBs are very appealing both from fundamental and technological point of view. In the former case the dynamic structure and lateral heterogeneity of the lipid bilayer can be studied, whereas, in the latter, SLBs open interesting possibilities for the development of bio-sensors. We study the thermodynamic properties of supported lipid bilayers (phase transitions) and protein/lipid interactions by using liposome-reconstituted membrane proteins. Particularly, we are interested in the distribution of integral membrane proteins in relation to lateral heterogeneity in the lipid bilayer [1,2].
We investigate how the variation of thermodynamic parameters such as temperature, solution ionic strength, pH and presence of an applied potential affect the lateral heterogeneity and the mechanical parameters of the membrane (3,4,5). Exploiting Black Lipid Membranes we relate the obtained variations in the mechanical parameters to the deviations in the activity of membrane proteins such as ion channels (KcsA) at single molecule level (6).
Key references
1. Phase-transition-induced protein redistribution in lipid bilayers
H. M. Seeger, C. A. Bortolotti, A. Alessandrini, and P. Facci
J. Phys. Chem. B. 113, 16654-9(2009)
2. Unravelling lipid-protein interaction in model bilayers by AFM
A. Alessandrini and P. Facci
J. Mol. Recognit. 24, 387-396 (2011)
3. Effect of physical parameters on the main phase transition of supported lipid bilayers
H. M. Seeger, G. Marino, A. Alessandrini, and P. Facci
Biophys. J. 97, 1067-76, (2009)
4. Supported Lipid Bilayers on Mica and Silicon Oxide: Comparison of the Main Phase Transition Behavior
H. M. Seeger, A. Di Cerbo, A. Alessandrini, and P. Facci
J. Phys. Chem. B 114, 8926 (2010)
5. What do we really measure when we perform indentation experiments on supported lipid bilayers by AFM?
A. Alessandrini, H. M. Seeger, A. Di Cerbo, T. Caramaschi, and P. Facci
Soft Matter 7, 7054-7064 (2011)
6. Changes in Single K+ Channel Behavior Induced by a Lipid Phase Transition
H. M. Seeger, L. Aldrovandi, A. Alessandrini, P. Facci
Biophys. J. 99, 3675-3683 (2010)
(left) Sketch of the set-up for measuring the nanomechanical properties of supported lipid bilayers; (right) Scheme of a KcsA molecule in the lipid bilayer at the phase transition region. The channel is confined in the fluid (ld) domains and mainly excluded from the gel (so) ones.
research @ NanoBioLab