Abstract

Membrane proteins are compact, highly versatile proteins that work inserted in the lipid bilayers that separate the cell from its surroundings. They can act as transporters and pores, motors, switches and pumps of ions. They can sense touch, temperature, light and volume, and transduce energy. The large variety of functions of membrane proteins promises an equally large number of possible applications and devices. Membrane proteins constitute about 30% of all the proteins encoded in the human genome, and represent the most important class of drug targets: about 50%. However, only about 2% of the 3D structures in the Protein Data Bank are membrane proteins. The number of high-resolution structures is even smaller, mainly because of the difficulties in crystallising them. A main objective of atomic force microscopy (AFM) studies of proteins is to directly observe with high resolution their functional behaviour, particularly their conformational changes in response to drugs etc. in real time. We use AFM , Dynamic Force Spectroscopy (DFS) and High-Speed AFM * to study the structure and the mechanisms that membrane proteins use for functioning inserted in lipid bilayers. In particular, we have studied by DFS the role of tryptophan residues in membrane protein anchoring using synthetic WALP peptides. Experimental results are complemented by Molecular Dynamics simulations. We have used AFM and DFS to study the mechanical properties of Purple Membranes. The effect of salt and pH on the interaction between lipids and proteins, the electrostatics and the membrane cohesion were also investigated. I will show our work towards improving the resolution and sensitivity of AFM and High-Speed AFM in solution by studying short-range forces at the membrane-double layer region. Our high resolution studies reveal local variations of the force fields near the membrane surface, namely ions affecting locally protein-lipid interactions. Finally, I will present our studies on interfacing membranes and membrane proteins with nano-structures aiming at the fabrication of bioelectronic devices using carbon nanotubes, n-doped carbon nanotubes and nano-gap electrodes.