A method to probe the individual steps in bacterial cell wall synthesis should advance the search for more effective medicines.

Bacterial cell wall biosynthesis is the target for several clinically-used antibiotics, but currently there are only limited methods to study the process in vitro. Timothy Bugg and colleagues at the University of Warwick, UK, have used a series of fluorescent peptides to study the way bacterial cell walls are made. These systems are 'really hard to study,' said Bugg, 'since they involve complex, lipid-linked structures.'

Listeria © CDC

Gram-positive bacteria, such as Listeria, are enclosed by a thick cell wall, a protective mesh of sugars and amino acids that surrounds their lipid cell membrane. The wall is made by a cycle of enzyme-catalysed steps mediated by this membrane. Bugg's group concentrated on the early steps in the biosynthesis, occurring inside the cell. 

In a preliminary stage of the cycle, a short peptide binds to a lipid carrier molecule which tethers it to the membrane. The group prepared fluorescent versions of the precursor peptide and mixed them with Escherichia coli membranes. They found that the labelled peptides followed the natural biosynthetic route to be incorporated into the membranes, providing more than 100-fold increases in fluorescence as the peptide bound to the lipid carrier molecules. 

Bugg said that the method will also allow scientists to study the later stages in cell wall biosynthesis. For example, in the next stage, a sugar molecule adds to the peptide-lipid intermediate. This causes the system to 'flip' to the outside of the membrane, ready to be used in the cell wall.

'The later stages of cell wall biosynthesis are really good targets for antibacterial medicines,' said Bugg. 'New antibiotics are needed urgently in the face of increasing resistance to clinical antibiotics.'

Michael Spencelayh