Individual proteins can be counted in a single cell.

It’s small-scale science that could have a massive impact on research into cell biology. Scientists in the US have produced a microscopic laboratory where they can count individual proteins in a single cell. 

It is already possible to interrogate the contents of a single cell, most often by tagging proteins with fluorescent dyes and watching them move around the cell. But such methods only enable the study of a few proteins at a time and do not reveal how many of each type there are. Moreover, the cell environment can confuse the fluorescent signal coming off the cells. 

The new method of protein analysis offers a unique approach to studying cell function.  ’This is the first time that the chemical contents of a cell have been measured by counting individual molecules,’ said Richard Zare, professor of chemistry at Stanford University, California. This opens up the possibility of studying proteins such as signalling molecules that might be present in very low numbers but are crucial to cell function, he said.   

Zare and colleagues have engineered microscopic channels, half the width of a human hair, into tiny squares of polydimethylsiloxane. A single cell introduced into a reaction chamber at the centre of the square is lysed and its contents are tagged. The fluorescing juice is drawn along one of the channels by electrophoresis and the researchers can then conduct a headcount of each type of protein as it streams past a detection point. ’It’s like being on a freeway at night and watching cars go by,’ said Zare.   

This improves on existing methods of protein analysis which struggle when there are fewer than around 100 molecules of a particular protein, said Thomas Pollard, professor of molecular, cellular and developmental biology at Yale University, Connecticut. But there’s an obvious drawback. ’By lysing the cell, one loses the spatial information provided by imaging methods,’ Pollard noted.

This cannot replace in vivo studies, agreed Zare. But it should prove a useful new tool for the molecular biologist. ’These are baby steps in the direction of something that I hope will some day usher in a revolution of how we analyse cells,’ he said.

Henry Nicholls