Septin proteins take bacterial prisoners

Cellular proteins called septins might play an important part in the human body’s ability to fight off bacterial infections, according to a study. Septins are found in many organisms, and are best known for building scaffolding to provide structural support during cell division and to rope off parts of the cell. However, most studies of septins, or guanosine-5′-triphosphate (GTP) binding proteins, have been confined to yeast cells. The latest research in human cells suggests that septins build ‘cages’ around bacterial pathogens, immobilizing the harmful microbes and preventing them from invading other healthy cells. This cellular defence system could help researchers to create therapies for dysentery and other illnesses, the researchers say. “This is a new way for cells to control an infection,” says Pascale Cossart, a cell biologist at the Pasteur Institute in Paris, who presented the findings in a poster session at the annual meeting of the American Society for Cell Biology in Denver, Colorado.

The researchers discovered the caging behaviour with Shigella, a bacterium that causes sometimes lethal diarrhoea in humans and other primates. To propagate from cell to cell, Shigella bacteria develop actin-polymer ‘tails’, which propel the microbes around and allow them to force their way into neighbouring host cells. To counterattack, human cells produce a cell-signalling protein called TNF-α. The researchers found that when TNF-α is present, thick bundles of septin filaments encircle the microbes. This, in turn, interferes with tail formation and stops Shigella in its tracks. Microbes that become trapped in septin cages are broken down in a stage of the cell’s life cycle called autophagy. “Autophagy is more efficient because of the septin cage, and the septin cage does not occur if you do not have the autophagy,” says Cossart.

January 10, 2012

Original web page at Nature