Researchers at the University of Groningen have succeeded in experimentally determining the maximum diameter of a pore in a cell membrane. They achieved this by directing a series of organic molecules that gradually increased in size through the pore. The diameter turned out to be significantly larger than had previously been calculated with the help of models from molecular dynamics. The research, on which biologists and chemists worked closely together, was published this week in the Early Edition of the scientific journal PNAS.
Every living cell is surrounded by a membrane that separates the content of the cell from the outside environment. However, the membrane is permeable to proteins that are secreted. The proteins are then conducted in an unfolded form through the membrane via a pore. The pore is very flexible and precisely envelopes the unfolded protein. This prevents other components of the cell leaking out during the secretion process.
In order to determine the maximum size of the pore opening, the researchers connected a series of size-gradated rigid, spherical organic molecules to a protein. As long as these were relatively small molecules, they were transported without problem through the pore together with the protein. As their size increased, however, there came a moment when the pore became blocked.
In this way it turned out to be possible to experimentally determine the maximum size of the pore. This was determined as about 2.2 nanometres (i.e. 2.2 hundred-thousandths of a millimetre). Previously, using simulation methods from molecular dynamics, the maximum diameter was estimated to be about 1.8 nanometres.
Prof. Arnold Driessen (department of Molecular Microbiology)
Prof. Ben Feringa (department of Organic Synthetic Chemistry)
Probing the SecYEG translocation pore size with preproteins conjugated with sizable rigid spherical molecules. Francesco Bonardia, Erik Halzab, Martin Walkob, François Du Plessisa, Nico Nouwena, Ben L Feringa and Arnold J. M. Driessen
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