Botulinum Toxin Deactivated by One Slight Change

A researcher at Brookhaven National Laboratory mutated a botulinum enzyme by just one amino acid, and abolished its toxicity.  The mutation, a change from a glutamate to a glutamine at one position, increased the distance from a zinc atom to a water molecule by 0.6 angstrom, less than one tenth of a billionth of a meter.  This was enough to prevent the botulinum enzyme from cleaving its target protein, a neurotransmitter.  The modified enzyme could still bind to it, but not cleave it.

This experiment points out the specificity of enzymes.  We are led to believe that evolution works by mutating things recklessly, but look how slight a change totally disarmed this enzyme.  A second observation is that toxins like botulinum might have originally had a beneficial function, but became toxic through degenerative mutations.  Though difficult to prove, it is an interesting suggestion that, just as with mentally ill humans, it doesn’t take much to turn a benign individual into a killer.  That isn’t evolution.  It’s a breakdown in quality control.  Another possibility is that botulinum’s function, cleaving a neurotransmitter, was originally beneficial.  As reported before, many deadly poisons actually follow a “hormesis” curve and only become harmful above certain levels (see 02/12/2003 headline).  Botox is now all the rage.  In minute amounts, it is proving versatile for everything from beauty treatments to tumor reduction; see for instance this report on EurekAlert about University of Pittsburgh scientists using to ease symptoms of enlarged prostate.