One of my favorite memories from growing up in West Virginia was traveling through the East River Tunnel. The tunnel is almost a mile long and remarkably spacious.
Construction of the tunnel began in 1969 and was completed in 1974. At the time, the project was the most expensive ever carried out by the West Virginia Department of Highways, costing 40 million dollars. It was extremely difficult to build, but the cost and effort were well worth it. The tunnel now serves as one of the major connectors between West Virginia and Virginia, but prior to its opening, the only passage over East River Mountain was a narrow, twisty road that became perilous in snow or fog.
Perhaps the enjoyable experience of driving through the East River Tunnel later affected my work as a biochemist. Among my favorite systems to study are the tunnels connecting the interior compartments of the cell to the exterior environment. These tunnels, made up of proteins, form pores that allow materials to pass through cell membranes.
One of the defining features of membrane channels are their specificity—allowing the transport of particular materials through the membrane, while excluding others. This selectivity depends on the precise positioning and spatial orientation of amino acid residues lining the membrane pores. Over the last half-century, biochemists have discovered time and again that molecular precision and fine-tuning define almost all biochemical systems, not just membrane channels. Biochemical exactness far exceeds the best efforts of human designers.
Precision and fine-tuning are also hallmarks of systems produced by human designers. These features are synonymous with exceptional quality. So from my perspective as a Christian apologist, the structural fine-tuning and molecular-level precision suggest that a Creator is responsible for making life
Aquaporins (and the closely related aquaglyceroporins) serve as an excellent example of the molecular fine-tuning that characterizes biochemical systems. These channels provide conduits for water (glycerol and related materials for aquaglyceroporins) to flow in and out of the cell. Aquaporins and aquaglyeroporins channels are unusually selective, transporting only water and glycerol across the cell membrane, respectively. They exclude all other materials, even hydrogen ions (protons).1 These two protein channels appear ubiquitous throughout nature, signifying their physiological importance. Biochemists have discovered aquaporins in mammals, amphibians, insects, plants, and an assortment of microbes.
Aquaporins reside within the phospholipid bilayer of the cell membrane. The aquaporin protein chain folds to form six bilayer-spanning segments. These bilayer-spanning regions organize within the cell membrane to create an hourglass-like structure. The six bilayer-spanning segments form two groups, each containing three membrane-spanning regions, separated by a narrowly constricted region within the membrane. The water channel is housed within the constriction.
As I discuss in The Cell’s Design, studies on a variety of aquaporins indicate that the selectivity of these channels depends on: (1) the pore size of the channel; (2) the specific identity and precise location of amino acids that line the channel; and (3) the exacting orientation of water molecules within the channel. New work provides additional insight into the selectivity mechanism of aquaporins and aquaglyeroporins.2
It turns out the higher order structure of the amino acids lining the channel interior is also a critical factor in the selectivity of these biomolecules. Researchers from Italy and Britain examined the channel structure of ten different aquaporins and aquaglyeroporins. They calculated the electrostatic profile within the channel produced by the ensemble of amino acid residues lining the walls. It turns out the electrostatic profiles displayed by aquaporins and aquaglyeroporins inside the pore are different. Aquaglyeroporins have a rather flat profile, whereas aquaporins have a more complex one characterized by maxima at the channel mouth at the constriction site. The investigators also discovered that substituting a single amino acid within the channel’s interior could radically alter the profile, transforming the channel from a water pore to one that transports small molecules like glycerol.
In The Cell’s Design, I argue that the salient characteristics of biochemical systems, such as their precision, are identical to features we would immediately recognize as evidence for the work of a human designer. The similarities between biochemical systems and manmade machines logically compels the conclusion that life’s most fundamental processes and structures stem from the work of an intelligent Agent.
Research on aquaporins and aquaglyeroporins helps connect scientific advancement with the Christian faith and tunnels through the mountain of intellectual doubt.
- Mario Borgina et al., “Cellular and Molecular Biology of the Aquaporin Water Channels,” Annual Review of Biochemistry 68 (1999): 425–58.
- Romina Oliva et al., “Electrostatics of Aquaporin and Aquaglyceroporin Channels Correlates with Their Transport Selectivity,” Proceedings of the National Academy of Sciences, USA 107 (2010): 4135–40.