“All of the life forms on Earth have the same problem,” said Jonathan Kagan, an immunology researcher at Boston Children’s Hospital. “And that is dealing with infection.” Just as we worry about bacterial infections, bacteria are on the watch for the viruses called phages that infect them, and — like every organism across every kingdom of life — they have evolved an arsenal of molecular tools to fight infections.
Large, complex creatures like humans can splurge on immense immune systems of specialized cells that detect or destroy invaders. Simpler organisms such as plants and bacteria often need to rely instead on suites of multitasking proteins that, like Swiss Army knives, are equipped for both jobs. Because defense is such a universal concern, it’s not surprising that many of these defensive systems have been preserved through evolution and shared among diverse organisms, including humans.
But a new study published this month in Science discovered that a family of proteins in bacteria and archaea, the simple prokaryotic cells that are the oldest form of life, detect viruses in a way never seen before.
Because of advances in gene sequencing and bioinformatic techniques, many of the antiviral defenses that bacteria use have started to come into view only within the last 50 years. But interest in them has ballooned in the past decade due to the powerful gene-editing tool that harnesses the bacterial CRISPR-Cas9 system. The tool’s success has prompted researchers to give more focus to how bacterial molecules recognize viruses and eliminate them.
Some of these antiviral defenses, such as CRISPR-Cas9, recognize specific sequences in the DNA that a phage injects into its host. Others don’t directly sense fragments of the virus but respond to evidence of the harm the virus causes, such as damaged DNA or malfunctioning cellular processes — the molecular equivalents of the broken glass at the scene of a break-in.
But the bacterial immune sensors called Avs proteins don’t do either, as researchers led by Feng Zhang of the Massachusetts Institute of Technology and Eugene Koonin of the National Center for Biotechnology Information have now discovered. Avs proteins can directly detect viral proteins manufactured by the cell’s hijacked machinery. [Continue reading…]