Where do new genes and complex proteins come from? For intelligent design creationists, gaps in our knowledge are opportunities to invoke a supernatural designer. For scientists, they are opportunities to investigate. A discovery reported in PNAS illustrates the difference: researchers have identified a functional protein in a giant virus that offers clues to the evolutionary origins of a more elaborate family of cellular proteins.
The proteins concerned are tandem potassium channels, which allow potassium ions to cross cell membranes. In humans, members of this family help stabilise the electrical potential across membranes and regulate the excitability of nerve cells. Their distinctive architecture includes two linked pore-forming domains within each protein subunit. Although simpler precursors of other potassium-channel families are known from bacteria, the evolutionary origins of this tandem arrangement have remained uncertain.
The researchers found a gene encoding such a channel in Pyramimonas orientalis virus, which infects a single-celled marine alga. Its protein, named Kpov, contains just 178 amino acids, yet experiments in artificial membranes confirmed that it functions as an ion channel with a preference for potassium over sodium. Here, then, is a comparatively simple working version of a molecular structure associated with more elaborate cellular machinery.
The evolutionary analysis adds a particularly interesting twist. The results suggest that the virus did not simply acquire this gene recently from its host. Instead, the channel may have originated through the fusion of simpler viral pore-forming components. This supports the possibility that viruses have contributed both genetic material and molecular innovations to cellular evolution.
