A scientific revolution?
The prion anomaly may challenge the central dogma of molecular biology
Alain E. Bussard
Alain E. Bussard is Honorary Professor at the Pasteur Institute, Paris, France.
Science, Thomas Kuhn argued in The Structure of Scientific Revolutions (1962), proceeds at two different paces. One is what he called "normal science", which professionals, the general public, the press and politicians generally understand as "research firmly based upon one or more past achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice." This stepwise progression towards a better understanding of Nature, by building on established knowledge, has been described in a myriad of textbooks, dictionaries and scientific papers.
However, Kuhn distinguishes this form of knowledge creation from so-called "puzzle-solving science". The latter results from anomalies—experimental observations or other evidence—which do not fit into the widely accepted theoretical framework of how Nature functions. Puzzle-solving science, according to Kuhn, can therefore trigger a scientific revolution as scientists struggle to explain these anomalies and develop a novel basic theory to incorporate them into the existing body of knowledge. After an extended period of upheaval, in which followers of the new theory storm the bastions of accepted dogma, the old paradigm is gradually replaced. Perhaps the best example of such a paradigm shift in science is the Copernican revolution in cosmology: the move from a geocentric to the heliocentric view of our solar system. Curiously, although Aristarches had already laid the seeds of heliocentrism in the third century BC, it took another 18 centuries before Nicolaus Copernicus proposed that the Earth moves around the sun and not vice versa. Many anomalies, such as the orbit of Mars, were already known at that time, but the power of the Aristotelian dogmas, including the geocentric view of the universe, was too strong to be overcome easily. Truly speaking, however, the notion of a paradigm, as defined by Kuhn, does not have exactly the same meaning in cosmology, physics,
Is the central paradigm of molecular biology...the only possible explanation of how life evolved, or are there other mechanisms of heredity in living organisms?
What I propose here is that biology is heading towards a similar scientific revolution that may shatter one of its most central paradigms. The discovery of a few small proteins with anomalous behaviour is about to overcome a central tenet of molecular biology: that information flows unidirectionally from the gene to the protein to the phenotype. It started with the discovery that prions, a class of small proteins that can exist in different forms, cause a range of highly debilitating diseases. This sparked further research, particularly by Stanley Prusiner at the University of California, San Francisco (USA), who eventually established that prions induce conformational changes in other proteins and thus transmit their conformational information. More recent research by Susan Lindquist at the Whitehead Institute (Cambridge, MA, USA) and Eric Kandel at Columbia University (New York, NY, USA) indicates that this may well be a form of protein-based information flow, which seems to be important in various biological processes ranging from the establishment of long-term memory to the adaptation of organisms to new environments.
Now we may have to abandon another concept...namely that the primary structure of a protein determines its tertiary structure
Scientific revolutions are still rare in biology, given that the field, unlike astronomy or physics, is relatively young. Until the middle of the eighteenth century, biology was essentially a descriptive activity rooted in medicine and observations of living Nature. Early biologists did not practise large generalizations as was the norm in physics or chemistry. During the eighteenth century, biologists started to ask themselves how they could explain the enormous variability of living organisms and their ability to adapt to their environment. Early thinkers, such as Jean-Baptiste Lamarck, Erasmus Darwin or Georges Louis Leclerc de Buffon suspected that environmental factors, over time, trigger physiological changes in the organism, which help it to cope with its surroundings. Lamarck's central example was the long neck of the giraffe, which he thought was the result of the animal stretching its neck to reach leaves high up on trees.