area in hot water. It is akin to what happens to the white
of an egg when you boil it. Being proteinaceous, such
toxins are also easily broken down by the digestive
system, hence the ability to drink snake venom with little
ill effect - unless of course you have any lesions in your
mouth or oesophagus (do NOT try this at home!).
So venom is a complex mixture of large, mostly proteina-
ceous compounds that are only toxic if delivered directly
into a victim’s tissue? Well, nearly. Cue the deadly blue-
ringed octopus (Hapalochlaena spp.). While the powerful
venom of these tiny cephalopods is primarily used for
predation, it is infamous in its ability to drop a human
within as little as 15 minutes after being bitten. This is
thanks to a potent neurotoxin called tetrodotoxin.
However, tetrodoxton is a small, non-proteinaceous
molecule that is also lethal if ingested, meaning that it is
both a venom and a poison, depending on the mode of
delivery.
While it is possible to generalise regarding the
differences in biochemical characteristics of most venom
toxins versus most poison toxins, the former are actually
defined by their mode of delivery and the functional role
they serve within the victim’s body, together with their
chemical properties. So just how do toxins work once
injected?
Potent precision.
As the active site of a venom toxin is of a very specific
configuration, it follows intuitively that toxins have
distinct molecular targets in the victim’s body. That is, a
given toxin type will target a specific cell receptor or
protein, for example, following the ‘lock-and-key’
metaphor. Venom toxins usually target cells and
molecules that have some kind of regulatory role, for
example the regulation of bleeding (haemostasis) or
neurotransmission. Each of these processes is regulated
by numerous different receptors, cells and molecules; for
example, there is not a single protein which regulates
bleeding, but dozens.
All of these regulatory processes are collectively referred
to as homeostasis - the maintenance of stable and
optimal conditions - and toxins work by upsetting the
homeostatic balance. This could be by inhibition (such as
a neurotoxin which blocks nerve signals to induce
paralysis), or it could be via stimulation (such as a
coagulotoxin which activates proteins in the blood to
induce rapid and extensive clotting).
While we commonly categorise venoms based on which
homeostatic process they disrupt - that is, which
pathology they induce (neurotoxic, haemotoxic,
cytotoxic, etc.) - this actually tells us very little about the
toxin itself. Toxins are instead classed by their structural
scaffold; their core structure. Their domains, however -
their active sites - vary from toxin to toxin, and this is
what determines their molecular target and activity.
Think of it as classing cars based solely on their type of
engine, where varying the tyres, shell, and overall size of
the car will determine its performance. Stick a 5.7L V8
engine into a VW Beetle and it will drive pretty differently
than the same engine in a Toyota Landcruiser fitted with
Mickey Thompsons – and I dare say that the two cars
would be likely to be driven to different destinations.
Along the same lines, one type of snake venom
metalloprotease (SVMP), for example, may activate a
specific protein which induces clotting, while another
SVMP may destroy proteins to cause haemorrhage.
Furthermore, a toxin’s activity will peak under its own set
of optimal conditions, such as a specific temperature and
pH - favourable track conditions, if you will.
Above: the Inland Taipan or Fierce Snake (Oyxuranus microlepidotus)