Date
Mon, 30 May 2005
17:00
Location
L1
Speaker
Richard D James
Organisation
Minnesota

Bacteriophage T4 is a virus that attacks bacteria by a unique mechanism. It

lands on the surface of the bacterium and attaches its baseplate to the cell

wall. Aided by Brownian motion and chemical bonding, its tail fibres stick to

the cell wall, producing a large moment on the baseplate. This triggers an

amazing phase transformation in the tail sheath, of martensitic type, that

causes it to shorten and fatten. The transformation strain is about 50%. With a

thrusting and twisting motion, this transformation drives the stiff inner tail

core through the cell wall of the bacterium. The DNA of the virus then enters

the cell through the hollow tail core, leading to the invasion of the host.

This is a natural machine. As we ponder the possibility of making man-made

machines that can have intimate interactions with natural ones, on the scale of

biochemical processes, it is an interesting prototype. We present a mathematical

theory of the martensitic transformation that occurs in T4 tail sheath.

Following a suggestion of Pauling, we propose a theory of an active protein

sheet with certain local interactions between molecules. The free energy is

found to have a double-well structure. Using the explicit geometry of T4 tail

sheath we introduce constraints to simplify the theory. Configurations

corresponding to the two phases are found and an approximate formula for the

force generated by contraction is given. The predicted behaviour of the sheet is

completely unlike macroscopic sheets. To understand the position of this

bioactuator relative to nonbiological actuators, the forces and energies are

compared with those generated by inorganic actuators, including nonbiological

martensitic transformations. Joint work with Wayne Falk, @email

Wayne Falk and R. D. James, An elasticity theory for self-assembled protein

lattices with application to the martensitic transformation in Bacteriophage T4

tail sheath, preprint.

K. Bhattacharya and R. D. James, The material is the machine, Science 307

(2005), pp. 53-54.

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