Gone fishing…for microscopic proteins

human cell
© iStock/Decha Rakjumroon

Using a new microscopic ‘fishing’ technique, researchers have successfully snagged thousands of proteins that are key to the formation of the cell skeleton.

Led by the Montreal Clinical Research Institute’s Jean-François Côté, the team used 56 ‘baits’ into human cells they were incubating in their laboratory, catching more than 9,000 proteins in the process.

The goal of this study was to identify the proteins that attach to those of the Rho family, famous in the cell biology world since the discovery in the early 1990s that they dictate how pieces of the cell skeleton, the ‘cytoskeleton’, are constructed.

The 20 members of the Rho family are scattered on the inner surface of cell membranes and act like switches. When a signal from outside or inside the cell activates them, they stimulate other proteins to force the cytoskeleton to add or remove parts to its framework.

To date, only three of these proteins have been thoroughly studied by researchers; the Cdc42 protein, Rac1 and RhoA. Cdc42 acts as the lead protein: it indicates the path that white blood cells must take to find a site of infection.

Rac1 activates the engines that drive a non-muscular cell forward. RhoA stimulates the formation of fibres that allow cells to contract or form resistant tissues as they come together to produce for example, the wall of a blood vessel.

Human cells growing in incubators in the laboratory allow scientist to cast their baited lines. This forces these cells to produce proteins with two heads, one containing a single side of a protein in the Rho family, the other a ‘biotin ligase’ enzyme. The latter acts as an elite sniper in the cell luring and labelling every passing protein with the help of its partner, a member of the Rho family. Every protein that approaches the bait was thus labelled with biotin.

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