Enzymes as mechanical devices

[Craig Marshall]

I like the idea very much. The serpins, a group of (mostly) serine
protease inhibitors have a number of features that I believe are best
explained by a mechanical analogy. They exist in two forms; an intact
and active form, and an inactive and cleaved form. Inactivation is
associated with interaction with an appropriate protease and the
subsequent slow release of the cleaved inhibitor. The two forms show
very different thermal stabilities, and most interestingly intact
serpins show little helical structure as detected by fourier-transform
infrared spectroscopy. After cleavage helical signal is found. X-ray
structures of four cleaved (or essentially so) serpins indicate that
there are definitely helices in the structure. I have imagined that
the helices act as springs and are thus slightly under or over-wound
in the intact molecules, and this provides the force that allows the
substantial changes in structure believed to be associated with the
inhibitory mechanism. Amongst these is the insertion of a further
strand into a beta-sheet.

I would be interested in any other examples that might support (or
refute) the idea of mechanical enzymes.

--
        Craig Marshall          	craigm at sanger.otago.ac.nz or
        Biochemistry Department 	bioc07 at otago.ac.nz
        University of Otago     	Phone 64 3 479 7849   	
        P.O. Box 56             	Fax   64 3 479 7866   	
        Dunedin, New Zealand