Sticky sugar

The sugar coating on cells allows them to find and stick with their brethren, based on results presented on page 529 by Bucior et al. The results show that, like proteins, carbohydrates alone are able to bind strongly to other specific carbohydrates.

The ability of cells to find others like themselves was first shown in sponges, when a mixture of single cells from two different sponges was seen to separate into the original two sets. This self-awareness relies on proteoglycans—extracellular proteins with long carbohydrate chains.

Since part of a proteoglycan is protein, it is easy to imagine that the protein component imparts specificity by forming a binding pocket that recognizes only self-sugars. But the new results show that proteins are dispensable in this process.

The group finds that a mixture of two sets...