Antibiotic resistance proteins identified

Scientists have identified two proteins that significantly increase the ability of disease-causing bacteria to resist some classes of antibiotics.

The finding could lead to development of drug therapies that can target bacterial resistance at its source.

The study, conducted by microbiologists from Ohio State University (US) and published online recently in the Proceedings of the National Academy of Sciences, focused on the activities of two genetically distinct forms of MprFs (multiple peptide resistance factors).

The proteins, MprF1 and MprF2, were found to be key to the mechanism allowing bacteria to change the electrical charge of their cell membrane, which is how bacteria develop resistance to certain antimicrobial agents and is also a means of adapting their membrane to new environmental conditions — such as those provided by their host.

“Both of these proteins are potentially very good drug targets because, in theory, if you can target them and inhibit their action, you can make bacteria strains more susceptible to existing antibiotics,” said Michael Ibba, associate professor of microbiology at Ohio State and a co-author of the study.

Scientists have already observed that the cell membranes of many disease-causing bacteria can increase antibiotic resistance by changing their electrical charge from negative to positive. Many antibiotics carry a positive charge that attracts them to negatively charged bacteria cells.

Ibba said the findings could help understand the mechanics of Methicillin-resistant Staphylococcus aureus (MRSA), the ‘superbug’ responsible for thousands of difficult-to-treat infections each year.

“There is a dispute that remains unresolved as to whether or not this pathway we’re investigating is involved in MRSA. It is very unclear. By understanding the mechanism, we might be able to find out if this is involved in MRSA or not,” Ibba said.

Ibba and Hervé Roy, a postdoctoral researcher at the university and lead author of the study, investigated the activity of two forms of MprF from Clostridium perfringens, a common food poisoning pathogen.

They found the proteins affected the membrane’s charge by using a tRNA molecule to transfer amino acids to the lipids in the cell membrane. This led to modification of the membrane and a reversal of its charge.

Ibba and Roy found that both MprF1 and MprF2 perform the same function, but they use different amino acids to modify the membrane. MprF2 used the amino acid lysine, while MprF1 used alanine. This amino acid also contributes to cell membrane modification and seems to have additional functions that remain unknown.

“This is a new function that we discovered, that MprF1 uses alanine, which then allows the cell to finetune the properties of the membrane,” Roy said.

“Earlier studies found these effects on the membrane, but no one knew what protein caused it.”

One finding of the study, which could have important inferences for combating antibiotic resistance, is that the proteins can use the adapter molecule in a variety of forms to modify the membrane. When the researchers manipulated the tRNA’s structure and properties to match differences that would occur in different bacterial species, the proteins still recognised the molecule and used it to perform the amino acid transfer.

“This means that there is no species barrier for the spread of this virulence factor among other bacteria because this protein can recognise tRNA in any species, no matter what it looks like,” Roy said.

Ibba and Roy describe their findings as only the beginning of investigating the role of the MprF family of proteins in bacteria. They believe other amino acids could also be used to modify bacteria cell membranes and are investigating additional pathways within the cells that could lead to membrane remodelling.

 “We know the change to the membrane is key to resistance,” Ibba said.

“We now know there is not just one way that can happen. We have just found a second way an organism can do this, and it is able to make the change to the membrane in two different ways.

“From our findings there are almost certainly even more ways that the membrane can be modified and that’s what we’re looking for next.”

Information provided by the Ohio State University.