by PhilipJ on 6 October 2005
As reported in this week’s Nature, some pathogenic bacteria grow secretion systems to inject noxious proteins into other cells, but the mechanism is poorly understood. For starters, crystal structures for both the noxious protein “cannonballs” and the “cannon” itself have been solved, but the diameter of the cannonball is larger than the cannon!
The solution proposed (here, subscription required) involves a protein called InvC, an ATPase that can form hexameric structures. In in vitro experiments, the cannonball protein SptP, initially bound to a chaperone molecule SicP2, binds to InvC. Using the energy stored in ATP, InvC dissociates SptP from SicP2 (leaving the chaperone to return to the cellular milieu), and then unfolds SptP. This unfolded form of SptP is small enough to fit inside of the bore of the cannon, providing a viable way in which the mechanism might work!