What’s she building in there?
IMAGINE YOU’RE AN anaerobic bacteria. You’ve swam around eating up nutrients, but you can hear that biological clock ticking. It’s time to have your very own bouncing baby bacteria. But how do you guarantee that you and your daughter turnout exactly the same? Of course, your DNA will be unchanged, but what about everything else? What molecular interactions ensure that your daughter is exactly the same size as you—that you divide symmetrically at the midpoint?
Natalie Goto, an associate professor at the University of Ottawa’s Chemistry Department, sees protein as the machinery of life. Proteins bind molecules together in very specific ways and their interactions act as a clock, telling cells what phase of life they are in. Goto is interested in how the shapes of proteins mediate the interactions between them.
In order to divide symmetrically, rod-shaped cells must construct a new wall at their exact midpoint. In bacteria, this process is controlled by the Min family of proteins.
The protein called MinC inhibits wall formation, but only when it is binded with its sister protein, MinD. MinD likes to moor on the cell wall. MinC and MinD have an affinity for each other.—whenever MinC floats by a MinD, it cuddles up and forms a complex that stops the cell from growing a dividing wall.
But there’s one last member of the Min family: MinE. MinE continually pushes its sister proteins around. MinE shoulders its way between MinC and MinD, displacing MinC. Afterward, MinE leaves MinD, forcing it to dissociate from the wall and driving it from the middle toward the pole of the cell. With no MinC and MinD left at the centre to stop the formation of a new wall, the cell divides.
MinE has a special site in the cell that it uses to breakup MinC and MinD and push them from the centre. Goto found that MinE folds to keep this binding site wrapped inside itself. Only when MinE opens itself up can the site disunite the other pair of proteins. Goto suspects that by keeping the binding site inaccessible, MinE can specifically focus on chasing its sister proteins from the centre. By pushing MinC and MinD duos from the centre and into the poles, MinE frees the cell to form a new wall and divide symmetrically.