Cell Requires Two Keys to Let Cargo Pass

For high-security environments, guards sometimes require two independent authentication methods.  Before humans came up with this trick, the cells in their bodies were already using it.  Itoh and Camilli explain in the May 13 issue of Nature:¹

Our cells contain a series of distinct compartments that do different jobs and have different properties.  The membranes that clad each of these compartments – like the plasma membrane that encases the cell – are defined by precise molecular compositions, which are preserved despite the continuous influx and efflux of components in transit to and from other cellular locations.  Precision is the hallmark of this flow of traffic, too, which must be directed appropriately between compartments.  All of this is achieved, in part, by the reversible recruitment of regulatory proteins from other parts of the cell to specific membranes or membrane regions.  A growing amount of evidence hints that membrane lipids cooperate with membrane proteins to control this recruitment.

They refer to work by Godi et al. in Nature Cell Biology that shows a dual-key authentication mechanism in the cell.  With “at least two independent, but synergistic, mechanisms,” cargo is only allowed to bind to a membrane if it binds correctly to two cytosolic proteins.  This can be envisioned as a kind of code:

The interaction of cytosolic proteins with both lipids and proteins on a target membrane is an efficient dual-key strategy to control their recruitment to membranes.  Only when both the lipid-binding and protein-binding sites are engaged is the interaction with the membrane strong enough.  The two elements of the code can be controlled independently, affording the possibility of fine-tuning the spatial and temporal regulation of recruitment.

Itoh and Camilli provide no suggestions on how such a system might have evolved.

¹Toshiki Itoh and Pietro de Camilli, “Membrane trafficking: Dual-key strategy,” Nature 429, 141 – 143 (13 May 2004); doi:10.1038/429141a.

There’s a coded message in this story.  Can you decipher it?