A couple of interesting papers in the latest issue of PNAS!
At the molecular level of biology, the competition for favorable outcomes has been shaped by evolution, just as in more familiar examples from ecological biology. At both levels, this competition is often based on raw speed. There are differences, of course. Most notably, a race between molecules is more often determined by diffusional dynamics than by inertial dynamics. The driving forces on molecules typically comprise electrostatic nudges rather than thundering hooves digging into soil. Electrostatic interactions can be surprisingly effective, however. The rate of degradation of the neurotransmitter acetylcholine by the synaptic enzyme acetylcholinesterase is known to be increased by a factor of up to a few hundred as a result of “electrostatic steering” of the positively charged acetylcholine molecule toward the predominantly negative active-site region of the enzyme […]. This tends to optimize the clearing and resetting of neuromuscular junctions and other cholinergic synapses, which offered a clear competitive advantage to our successful ancestors, relative to more sluggish individuals of their species who faced the same predators. Such selective pressures are also recorded in proteins at the next level of a hierarchy, in some of the venom molecules of snakes such as the green mamba that prey on small mammals in sub-Saharan East Africa. The green mamba toxin fasciculin-2 is a small protein whose positively charged surface is attracted to, and clamps down on, the active-site entrance of acetylcholinesterase, causing muscular activity of the unfortunate rat or other prey to cease. Here, again, the binding involves electrostatically steered diffusion, and the binding speed is increased by a factor of up to a few hundred by the electrostatic attraction between the proteins (1). Many other examples of electrostatically steered, diffusion-controlled processes are now known, including such familiar ones as the polymerization of actin […]. In a recent issue of PNAS, a new article by Qin and Zhou greatly deepens our insight into these important processes, and extends the range of analysis to include reactions in which the rates may be influenced by events following the initial diffusional encounter […].
Emotion research has something in common with a drunk searching for his car keys under a street lamp. “Where did you lose them?” asks the cop. “In the alley,” says the drunk, “but the light is so much better over here.” For emotion research, the light shines most brightly on the face, whose movements can be coded, compared across cultures, and quantified by electromyography. All of the “basic” emotions described by Paul Ekman […] and others (happiness, sadness, anger, fear, surprise, and disgust) earned their place on the list by being face-valid. The second source of illumination has long been animal research. Emotions that can be reliably triggered in rats, such as fear and anger, have been well-studied, down to specific pathways through the amygdala […]. But emotions that cannot be found on the face or in a rat, such as moral elevation and admiration, are largely abandoned back in the alley. We know they are there, but nobody can seem to find a flashlight. It is therefore quite an achievement that, as described in this issue of PNAS, Immordino-Yang, McCall, Damasio, and Damasio […] managed to drag an fMRI scanner back there and have given us a first glimpse of the neurological underpinnings of elevation and admiration.