Ladislav Kovàč is a professor of biochemistry and cognitive biologist at the Biocenter of Comenius University in Bratislava, Slovakia. He founded the Laboratory of Comparative and Functional Genomics of Eukaryotic Organelles.
He is a strong advocate for seeing biological systems and subsystems as exhibiting cognition, even in some of the smallest biological structures. Jacques Monod suggested that even proteins have a kind of cognition in their ability to distinguish between substrates and ligands. Ligands that bind to cell receptors, such as activators, inhibitors, and neurotransmitters, can be considered as signaling the cell.
When the receptor undergoes a conformational change in response to the signal, we can say that the receptor "knows what to do" with the signal, and that the signal therefore has "meaning." Various receptors turn cells into "biological information-processing systems." They make the cells (and even sub-cellular organelles) into teleonomic (purposeful) agents. As Monod's colleague, François Jacob, put it, "the purpose of every cell is to become two cells."
Kovàč describes the process of recognition by molecules and their subsequent purposeful actions:
molecular recognition by
a protein molecule is only part of
the story. Recognition is followed
by an action. A ligand is a signal. In contrast
to standard chemical interactions, binding
energy is not fully dissipated as heat, but is
used partly for molecular work — a specific
pre-programmed change in the conformation
of the protein. In this way, the signal is
transmitted from one site on the protein to
another. The transmission takes place in
four-dimensional space, as it involves time
as a coordinate, and this process gives biochemistry
its vectoriality. The exploitation
of binding energy was originally recognized
in enzymatic catalysis, in which
a portion of the binding energy acts to
lower the activation energy of a reaction, but it can be expanded to
explain the work of translocators, receptors
and transcription factors.
By receiving and transmitting signals,
proteins execute a complete working
cycle in an ‘all or nothing’ fashion. It is
appropriate to regard most protein molecules
as molecular engines. Hence, molecular
cognition consists of molecular
sensation — which has two inseparable
aspects, recognition and signifaction —
and molecular action. As Monod
pointed out, by binding two or more ligands,
some proteins can bring them
together not on thermodynamic, but
exclusively on logical, grounds — the principle
of gratuity. By selective binding, proteins
also associate with each other to
form purposeful protein networks. In addition,
owing to their structural asymmetry,
protein molecules can use thermal energy
from the environment to perform work as
Brownian ratchets. It is essential to
acknowledge that all the activities of
a protein reside in its structure, which is
built in by evolution. In terms of Shannon’s
communication theory,
the exploratory behaviour of a protein
molecule — its constant change between
sub-states — is a manifestation of its information
entropy. The appropriate ligand
triggers pre-programmed responses; the
whole process is nothing more than a
one-bit information transaction.
Describing a protein as a cognizing agent would appear to be a blatant example of extreme anthropomorphism, but Kovàč's work is showing how human consciousness (defined as awareness of meaningful signals coming in and appropriate reactions going back out to the environment) may have evolved from the simplest forms of life, indeed from sub-units of life that are not themselves living systems.
The possible "actions" of a protein molecule are encoded in the possible conformations (different "foldings") of the protein. If it had a single conformation, it would be useless. As Shannon showed us, a system communicating information must have multiple "possible" messages. With only a single possibility, no new information could be communicated.
Changes in the conformation require energy with negative entropy. This is provided by the nearly universal energy carrier ATP, which dephosphorylates, giving up one phosphate group to become ADP. As Erwin Schrödinger said in "What Is Life?," life feeds on stream of negative entropy from the sun. We can see the conformational change, and the energy provided by ATP, in the working of the ion channel Na+/K+ (sodium-potassium pump) that moves ions back across the neuron cell membrane to restore the resting potential and prepare the cell for another activation spike.
For Kovàč, the proteins that make up the sodium-potassium pump are "sentient." They are exhibiting purposeful behavior when they change their conformation to allow in one type of ion, then change the conformation again to allow them out on the other side of the membrane.
He says that:
Each of the proteins we
encounter in nature is a product of evolution;
it has been selected to perform
a goal-directed teleonomic function.
For most natural proteins, the function
begins with the specific binding of a ligand.
But it is not the protein molecule as a
rigid structure that selects the appropriate
ligand. There are constant structural
changes between sub-states, even in the
absence of a ligand. When the ligand is
present, it binds to one particular sub-state
that the protein molecule is able to
adopt—it is therefore possible to say that
a protein molecule exhibits exploratory
‘behaviour’. This intrinsic goal-directed
plasticity of the protein molecule can be
dubbed ‘molecular sentience’, and it is this
sentience that makes a protein a ‘living’
molecule...
Sentience — the capacity to exhibit a variety
of potential internal states, which
respond to the immediate state of the environment—
might therefore constitute the
essence of life.
It is this purpose, built into the protein
structure, which allows us to call
protein–ligand interaction ‘molecular
recognition’. Because of this intrinsic
teleonomy, a protein gives meaning and
significance to its environment—that is, to
its ligand. By contrast, nomic interactions
of individual atoms and molecules, such
as chemical reactions in the inanimate
world, with no evolutionary history, are
inevitable, deterministic, timeless and do
not represent cognition.
|
