				Engineering for the Life Sciences Department of Engineering

Structure of biological molecules

The study of bacteria and DNA is not usually associated with engineering, but Professor Chris Calladine has applied his knowledge of structural mechanics in solving some fundamental problems in this area.

For instance, the structure of a trans-membrane protein, TolC, has recently been determined by Dr Ben Luisi's group in the Department of Biochemistry. The central portion of TolC is a simple cylindrical tube made from twelve alpha-helices stacked side-by-side. Now when two alpha-helices stack side-by-side they normally form a twisted "coiled coil"; and in order to stack in the manner of TolC, the a-helices must be untwisted. We have discovered, by studying the detailed geometry, and in particular the pattern of inter-residue distances, that the untwisting is achieved in nature by a particular pattern of large and small hydrophobic residues on the alpha-helix surface. It may be possible to design alpha-helices that assemble in a similar way to form "nano-tubes"; which could have widespread biotechnical implications.

We are also studying side-by-side packing of identical alpha-helices as "switching" devices that might be used by nature for the transmission of signals.

Contact: Professor Chris R. Calladine, email: crc at eng.cam.ac.uk, tel: +44 1223 332725.

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