News: Evolution's new wrinkle - Proteins with cruise control provide new perspective

Evolution's new wrinkle: Proteins with cruise control provide new
perspective

(PhysOrg.com) -- A team of Princeton University scientists has discovered
that chains of proteins found in most living organisms act like adaptive
machines, possessing the ability to control their own evolution.

The research, which appears to offer evidence of a hidden mechanism guiding
the way biological organisms respond to the forces of natural selection,
provides a new perspective on evolution, the scientists said.

The researchers -- Raj Chakrabarti, Herschel Rabitz, Stacey Springs and
George McLendon -- made the discovery while carrying out experiments on
proteins constituting the electron transport chain (ETC), a biochemical
network essential for metabolism. A mathematical analysis of the experiments
showed that the proteins themselves acted to correct any imbalance imposed
on them through artificial mutations and restored the chain to working
order.

"The discovery answers an age-old question that has puzzled biologists since
the time of Darwin: How can organisms be so exquisitely complex, if
evolution is completely random, operating like a 'blind watchmaker'?" said
Chakrabarti, an associate research scholar in the Department of Chemistry at
Princeton. "Our new theory extends Darwin's model, demonstrating how
organisms can subtly direct aspects of their own evolution to create order
out of randomness."

The work also confirms an idea first floated in an 1858 essay by Alfred
Wallace, who along with Charles Darwin co-discovered the theory of
evolution. Wallace had suspected that certain systems undergoing natural
selection can adjust their evolutionary course in a manner "exactly like
that of the centrifugal governor of the steam engine, which checks and
corrects any irregularities almost before they become evident." In Wallace's
time, the steam engine operating with a centrifugal governor was one of the
only examples of what is now referred to as feedback control. Examples
abound, however, in modern technology, including cruise control in autos and
thermostats in homes and offices.

The research, published in a recent edition of Physical Review Letters,
provides corroborating data, Rabitz said, for Wallace's idea. "What we have
found is that certain kinds of biological structures exist that are able to
steer the process of evolution toward improved fitness," said Rabitz, the
Charles Phelps Smyth '16 Professor of Chemistry. "The data just jumps off
the page and implies we all have this wonderful piece of machinery inside
that's responding optimally to evolutionary pressure."

The authors sought to identify the underlying cause for this self-correcting
behavior in the observed protein chains. Standard evolutionary theory
offered no clues. Applying the concepts of control theory, a body of
knowledge that deals with the behavior of dynamical systems, the researchers
concluded that this self-correcting behavior could only be possible if,
during the early stages of evolution, the proteins had developed a
self-regulating mechanism, analogous to a car's cruise control or a home's
thermostat, allowing them to fine-tune and control their subsequent
evolution. The scientists are working on formulating a new general theory
based on this finding they are calling "evolutionary control."

The work is likely to provoke a considerable amount of thinking, according
to Charles Smith, a historian of science at Western Kentucky University.
"Systems thinking in evolutionary studies perhaps began with Alfred
Wallace's likening of the action of natural selection to the governor on a
steam engine --- that is, as a mechanism for removing the unfit and thereby
keeping populations 'up to snuff' as environmental actors," Smith said.
"Wallace never really came to grips with the positive feedback part of the
cycle, however, and it is instructive that through optimal control theory
Chakrabarti et al. can now suggest a coupling of causalities at the
molecular level that extends Wallace's systems-oriented approach to this
arena."

Evolution, the central theory of modern biology, is regarded as a gradual
change in the genetic makeup of a population over time. It is a continuing
process of change, forced by what Wallace and Darwin, his more famous
colleague, called "natural selection." In this process, species evolve
because of random mutations and selection by environmental stresses. Unlike
Darwin, Wallace conjectured that species themselves may develop the capacity
to respond optimally to evolutionary stresses. Until this work, evidence for
the conjecture was lacking.

The experiments, conducted in Princeton's Frick Laboratory, focused on a
complex of proteins located in the mitochondria, the powerhouses of the
cell. A chain of proteins, forming a type of bucket brigade, ferries
high-energy electrons across the mitrochondrial membrane. This metabolic
process creates ATP, the energy currency of life.

Various researchers working over the past decade, including some at
Princeton like George McClendon, now at Duke University, and Stacey Springs,
now at the Massachusetts Institute of Technology, fleshed out the workings
of these proteins, finding that they were often turned on to the "maximum"
position, operating at full tilt, or at the lowest possible energy level.

Chakrabarti and Rabitz analyzed these observations of the proteins' behavior
from a mathematical standpoint, concluding that it would be statistically
impossible for this self-correcting behavior to be random, and demonstrating
that the observed result is precisely that predicted by the equations of
control theory. By operating only at extremes, referred to in control theory
as "bang-bang extremization," the proteins were exhibiting behavior
consistent with a system managing itself optimally under evolution.

"In this paper, we present what is ostensibly the first quantitative
experimental evidence, since Wallace's original proposal, that nature
employs evolutionary control strategies to maximize the fitness of
biological networks," Chakrabarti said. "Control theory offers a direct
explanation for an otherwise perplexing observation and indicates that
evolution is operating according to principles that every engineer knows."

The scientists do not know how the cellular machinery guiding this process
may have originated, but they emphatically said it does not buttress the
case for intelligent design, a controversial notion that posits the
existence of a creator responsible for complexity in nature.

Chakrabarti said that one of the aims of modern evolutionary theory is to
identify principles of self-organization that can accelerate the generation
of complex biological structures. "Such principles are fully consistent with
the principles of natural selection. Biological change is always driven by
random mutation and selection, but at certain pivotal junctures in
evolutionary history, such random processes can create structures capable of
steering subsequent evolution toward greater sophistication and complexity."

The researchers are continuing their analysis, looking for parallel
situations in other biological systems.

Provided by Princeton University
http://www.physorg.com/news145549897.html

Posted by
Robert Karl Stonjek


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