Flicking the acetyl switch

A strain of Escherichia coli that can produce proteins containing an acetylated version of the amino acid lysine could help to reveal how acetylation changes the function of hundreds of proteins inside cells.

Acetylation occurs naturally in cells and is thought to regulate many important processes including the copying and repair of DNA. But the mechanism is poorly understood because researchers have had no way to add an acetyl group CH₃C(O) to the end of specific amino acids and see what effects this has on a protein’s behaviour. 

Now, Jason Chin and colleagues at the Medical Research Council’s Laboratory of Molecular Biology, Cambridge, have created a strain of Escherichia coli that can produce proteins containing the acetylated form of lysine (acetyllysine) at particular sites. 

To make their E coli, the researchers modified an enzyme used by a different species of bacteria, the methane-producing strain Methanosarcina barker. M barker bacteria naturally insert another form of lysine - pyrrolysine - into some proteins. The enzyme - an aminoacyl tRNA synthetase - is part of the assembly line of enzymes responsible for taking the DNA message and turning it into a protein. 

The researchers mutated a few amino acids in this enzyme so that it picked up acetyllysine instead of pyrrolysine. They then spliced DNA coding for their new enzyme into E coli and found the engineered bacteria were able to produce proteins containing acetylated lysine. 

Chin’s team now hopes to look at how acetylation affects histone, the protein ’spool’ around which DNA is wound in chromosomes. The protein helps to unravel DNA so that it can be read and copied and acetylation is thought to play a key role in the process. 

’We don’t know how that works at all, so having the facility to make completely homogenous preparations of chromatin with acetylations on histone molecules at particular sites will allow us to look at this in very clean experiments,’ Chin explains. He believes it may also shed light on the phenomenon of epigenetic inheritance, in which a dividing cell passes information on to its daughter cells that is not directly coded into the DNA. 

Commenting on the work, Louis Mahadevan, of the department of biochemistry at the University of Oxford, told Chemistry World, ’If the method finds its way into routine usage, it could be extremely useful, and would enable experiments to be carried out that have previously not been possible.’ 

John Bonner