Viruses infecting marine picoplancton encode functional potassium ion channels

Phycodnaviruses are dsDNA viruses, which infect algae. Their large genomes encode many gene products, like small K⁺ channels, with homologs in prokaryotes and eukaryotes. Screening for K⁺ channels revealed their abundance in viruses from fresh-water habitats. Recent sequencing of viruses from marine algae or from salt water in Antarctica revealed sequences with the predicted characteristics of K⁺ channels but with some unexpected features. Two genes encode either 78 or 79 amino acid proteins, which are the smallest known K⁺ channels. Also of interest is an unusual sequence in the canonical α-helixes in K⁺ channels. Structural prediction algorithms indicate that the new channels have the conserved α-helix folds but the algorithms failed to identify the expected transmembrane domains flanking the K⁺ channel pores. In spite of these unexpected properties electophysiological studies confirmed that the new proteins are functional K⁺ channels.