Membrane Proteins Caught On Camera

Using high-speed atomic force microscopy (AFM), an international team of researchers has captured on film the motions and interactions of membrane proteins (Nat. Nanotechnol., DOI: 10.1038/nnano.2012.109). Scientists have used fluorescence microscopy to examine the dynamics of membrane proteins before, says team leader Simon Scheuring of the French National Institute of Health & Medical Research. But those experiments required that the protein be fluorescently labeled, he says. They also typically followed the motion of only one protein at a time. Scheuring’s team sees all the proteins in the membrane with AFM, he notes, and therefore learns how the diffusion of a protein is affected by its molecular environment. To make the AFM measurements, Scheuring and colleagues deposited the Escherichia coli membrane protein OmpF, along with some E. coli lipids, onto a mica support. The researchers found that OmpF proteins move slowly over short distances when in crowded areas and wander at a faster pace over longer distances in loosely packed regions. Combining AFM data with molecular dynamics simulations, they also generated a potential energy map of protein-protein interactions. Developing techniques that assess how proteins “play” with each other, Scheuring points out, is vital to understanding cellular function.