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A small fungal enzyme could play an important role in simplifying the development and manufacture of drugs, according to scientists at Rice University.
The Rice lab of chemical and biomolecular engineer Xue Sherry Gao and colleagues isolated a biocatalyst known as CtdE after identifying it as the natural mechanism that controls the chirality – left handedness or right – handedness – of compounds produced by the native fungal host.
The open access study appears in Nature Communication.
Two chiral things are, like the hands, similar in structure but cannot overlap perfectly. Because property is important in the design of drugs that bind well to their targets, the ability to achieve 100% correct chirality is highly desired, Gao said.
“This is important because if a pharmaceutical drug has the wrong stereochemistry (three-dimensional chirality), it could become poison for humans, even though the planar chemical structure is the same,” she said.
Like the “left” or “right” orientation in chiral objects, what is called a 3S or 3R orientation is determined by the stereocenter of a molecule, a connection to an atom between parts of a molecule, has Gao said.
But while nature handles the process with ease, the selective synthesis of stereocenters has been a challenge for chemists. The entire mechanism behind nature’s ability to control whether a molecule has a 3S or 3R orientation has been hidden so far.
Understanding how it works in fungi and analyzing its structure could give scientists, especially those who design drugs, a new tool for chemical synthesis.
The aim of the study, a natural bioactive product known as 21R-citrinadine A, discovered in 2004 in a marine fungal strain of Penicillium citrinum, is toxic to leukemia in mice and lung cancer cells. human.
“21R-citrinadine A is a very complicated molecule, with eight stereocenters,” Gao said. “In a way, the article highlights how nature uses enzymes to synthesize a complex molecule with such precision. Eight different stereocenters are a lot to control.”
She said the molecule incorporates a “very intriguing” 3S spirooxindole ring. “Nature produces several other chemicals with a pharmacophore similar to spirooxindole,” Gao said. “However, we have become very curious that some of them contain a 3R spirooxindole cycle, as opposed to the 3S in citrinadines.
“All of the genes responsible for expressing this small molecule are clustered together in these fungi, so we first found the gene cluster and looked at each gene individually to see which might be most important in catalyzing specific chemical transformations.” , she said.
“Once we find it, we can extract this gene from the fungus, put it back into a friendly host, E. coli, and then use protein purification technology to isolate and test its function in a test tube,” Gao said. . “By doing everything apart from the fungus, we can be sure that there is only one enzyme that performs this function.”
Modified E. coli express the bulk CtdE protein. When subsequently used in chemical transformations, CtdE catalyzed the desired 3S stereoselectivity at all levels. “A spirooxindole is already difficult to synthesize,” she said. “Our goal was to understand the mechanism by which the enzyme controls this specific 3S stereochemistry.”
Bioinformatics analysis, X-ray crystallography and experiments have confirmed that CtdE is the only one responsible for the catalysis of 3S stereoselectivity, Gao said. (Another enzyme, PhqK, was already known to catalyze the 3R orientation.) “Having a set of two enzymes that give precise control over stereochemistry will eventually improve synthesis in pharmaceutical production,” she said.
Gao noted that because CtdE works at room temperature, it will also help keep chemistry “green”. “I hope that these biocatalysts will catalyze chemical reactions in a more environmentally friendly way,” she said.
Postdoctoral fellows Zhiwen Liu and Fanglong Zhao de Rice and graduate student Boyang Zhao of Baylor College of Medicine are co-lead authors of the article.
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