When gonorrhea bacteria detect an antibiotic, scientists suspect they use a protein to “pump it out” and survive the medication.
Now scientists have described the structures of two protein pumps–one used by gonorrhea (the MtrF protein) and one used by Alcanivorax borkumensis (the YdaH protein), a rod-shaped bacteria found in oceans that feeds on oil.
The two are closely related members of the AbgT family of 13,000 proteins.
“There was no structural information for these proteins, and functional study of them was very limited,” says Edward Yu, a professor at Iowa State University and an associate of the US Department of Energy’s Ames Laboratory.
The studies reveal that when the bacteria detect the antibiotic sulfonamide, “they turn on these transporters and pump it out, assuring survival of the cell,” Yu says.
With further study, he says, researchers may be able to find ways to block the protein pumps and restore the effectiveness of the antibiotics.
Using x-ray crystallography, the researchers saw the MtrF and YdaH proteins were two-part molecules with nearly identical structures and bowl shapes. Both have the same number of transmembrane helices and hairpins. Both looked to be pathways in or out of the cell.
Initially, the researchers thought the proteins were a part of the cell membrane that imported metabolites into the cell to promote growth and division.
With further study, they concluded the two proteins are efflux pumps responsible for moving substances out of the cell. In these two bacteria, the pumps remove sulfonamide antibiotics, allowing the bacteria to survive treatment with the drugs.
Yu, who has studied other efflux pumps, says the studies of these two proteins have led him and his collaborators to hypothesize about the thousands of other members of the AbgT protein family: “This is a family of pumps,” he says. “In this family, there may be many members that serve as efflux pumps that protect cells.”
Source: Iowa State University