Chemical change: how bacteria deactivate albicidin

Chemical change

The resistant germs capture the albicidin drug with a mass produced protein and inactivate it.

BRAUNSCHWEIG. Many bacteria have naturally acquired mechanisms that protect them from harmful substances. The same goes for the drug albicidin: Klebsiella bacteria have a protein molecule called AlbA, which binds to albicidin and is therefore inactivated.

Scientists at the Helmholtz Center for Infection Research (HZI) and the Helmholtz Associated Institute for Pharmaceutical Research, Saarland (HIPS) have studied the mechanism of resistance with atomic resolution, reports the HZI.

They discovered that the protein not only binds but also chemically modifies the drug (J. Am Chem Chem 2018; 140 (48): 16641-16649). At the same time, it increases its own production, making albicidin even more effective.

Klebsiella pneumoniae is one of the most common pathogens of bacterial sepsis and hospital-acquired pneumonia, but it can also cause urinary tract infections, reminiscent of HZI. Klebsiella are gram-negative bacteria that are difficult to treat and often develop resistance to several antibiotics.

Cystobactamides are similar to albicidin

HZI scientists have already discovered a new class of drugs that work against Gram-negative bacteria: cystobactamides. "This class of substances is similar to albicidin, against which many strains of Klebsiella are already showing resistance," says junior professor Jesko Köhnke, who heads the junior research group "Structural biology of biosynthetic enzymes" at HIPS . "We wanted to know if AlbA protein is also active against cystobactamides and analyzed the mechanism of resistance to albicidin at the molecular level."

To this end, an interdisciplinary team of scientists led by Jesko Köhnke, responsible for the synthesis of Professor Mark Brönstrup, the working group led by bioinformatics professor Olga Kalinina and the department of activity testing and gene expression profiles from Professor Rolf Müller. First, the three-dimensional structure of AlbA protein with bound albicidin was deciphered by X-ray crystallography.

Scientists have noticed that a small binding pocket for the antibiotic had become a long tunnel during evolution, in which albicidin was inserted perfectly. The structural analysis also provided another amazing result: the bound albicidin was chemically modified. "At first, we assumed that AlbA simply absorbed albicidin – just like a sponge – and therefore eliminated it temporarily, but now we have found that it even changes albicidin," says Köhnke.

Altered albicidin has lower activity

Other experiments have shown that modified albicidin has a lower activity and is therefore less harmful to bacteria. Scientists have discovered that in addition to the antibiotic binding site, AlbA has one for DNA. With this section, it can bind to the genetic material of the bacterial cell – exactly where AlbA production is controlled.

In laboratory experiments on Klebsiella pneumoniae, the team led by Köhnke was able to demonstrate that, during the administration of albicidin, the gene containing the plan for AlbA was read 3000 times more often after four hours without antibiotics. "Klebsiell's mechanism against albicidin is extremely effective: if they come into contact with it, they capture the first molecules of the active ingredient with their AlbA protein, while at the same time they produce more and more AlbA. we have also been able to show that these mechanisms of resistance are not yet sufficient, which we now wish to study more closely, "said Köhnke.

Comparative experiments have shown that cystobactamide, a drug associated with albicidin, is significantly weaker bound by AlbA. In addition, it does not stimulate the production of AlbA, so that Klebsiella, with this mechanism, can not so far reach a resistance to cystobactamide. "Nevertheless, the bacteria are resistant to cystobactamide, so we want to elucidate the mechanisms as precisely as possible so we can then develop agents that bypass the resistance," Köhnke said. (Eb)