Thursday, February 3, 2011

A New Route to a Potent Antibiotic

Manipulating biosynthetic process may yield better drugs

Tufts University School of Engineering researchers have produced the antibiotic erythromycin A using Escherichia coli.
“The production of erythromycin A through E. coli offers a new route to a potent antibiotic product,” Blaine Pfeifer, PhD, assistant professor of chemical and biological engineering at Tufts, told Pharmaceutical Formulation & Quality. “In addition, the erythromycin biosynthetic process can now be manipulated completely within this new production platform for the generation of new erythromycin derivatives that may possess even greater antibiotic potential. More broadly, success in this case will further support the concept of heterologous biosynthesis as a route to similarly complex therapeutic natural compounds.”

Manipulating the Biosynthetic Pathway

This research is a huge leap forward in manipulating the biosynthetic pathway, according to Tilmann Weber, PhD, department of microbiology/biotechnology, Eberhard-Karls-Universität Tübingen in Germany.
Microorganisms produce many antibiotics as secondary metabolites. The enzymes responsible for the biosynthesis of these chemical molecules are among the most complex in nature, and their complexity makes it challenging to use them for genetic engineering, Dr. Weber said. Furthermore, most antibiotic producers are only distant relatives to model organisms, which means that for every producer, basic mutagenesis protocols must be reinvented.
“[This work] allows the manipulation of such complex biosynthetic pathways in E. coli, where much better molecular tools exists than in the original producer,” he said.
The more derivatives/novel compounds one can generate, the higher is the chance to find derivatives—or even designed molecules—with improved properties also against resistant pathogens.
—Tilmann Weber, PhD, Eberhard-Karls-Universität Tübingen
Erythromycin A and several erythromycin variants are derived from the bacterium Saccharopolyspora erythraea, which is found in soil. Engineering S. erythraea can be difficult. More than 20 genes must work together to produce the erythromycin molecule, some of which are larger than those typical for E. coli, Dr. Pfeifer said.
“As a result, the biosynthetic process can tax native gene expression machinery,” he added. “If expression is successful, several of the resulting enzymes form multi-unit complexes, require post-translational modification, and require additional cofactors for activity.”
The researchers have also seen that many of the resulting enzymes have protein-folding problems, which limit activity. These issues complicate the heterologous production of complex natural products like erythromycin, Dr. Pfeifer said.
This new production method has its own obstacles. The first challenge is plasmid incompatibility, which causes the system to exhibit genetic instability, Dr. Pfeifer said. In addition, the titers produced must be substantially improved if this method is to compete with currently available processes. “The engineering capabilities associated with E. coli are considered a primary means of overcoming this limitation,” he added.
The benefits of this production method outweigh any challenges, though. First, it appears to offer a more cost-effective method to produce erythromycin A than those already available. “If production levels from an E. coli system could match current technology, there would be an economic advantage to using E. coli from a production cost and speed perspective,” Dr. Pfeifer said. “Namely, the growth kinetics and simple nutrient requirements associated with E. coli would allow a faster, simpler, and cheaper production process.”

A Path to New Antibiotics?

This breakthrough may lead to new antibiotics, which could help fight antibiotic-resistant pathogens. The new production platform allows researchers to manipulate the erythromycin biosynthetic process, which could generate new erythromycin derivatives that possess even greater antibiotic potential, Dr. Pfeifer said.
“I hope the work attracts attention to a promising general approach for the overproduction of either established or new antibiotics with the capability of compound modification for the purpose of addressing bacterial resistance,” he said. In addition, the methodology could be applied to other natural products that are limited by their native biological production hosts.
“The more derivatives/novel compounds one can generate, the higher is the chance to find derivatives—or even designed molecules—with improved properties also against resistant pathogens,” Dr. Weber said.

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