Strain selection and scale-up fermentation for FR901379 acylase production by Streptomyces sp. no. 6907

Fermentation Titer Optimization and Impact on Energy and Water Consumption during Downstream Processing

A common focus of fermentation process optimization is the product titer. Different strategies to boost fermentation titer target whole-cell biocatalyst selection, process control, and medium composition. Working at higher product concentrations reduces the water that needs to be removed in the case of aqueous systems and, therefore, lowers the cost of downstream separation and purification. Different approaches to achieve higher titer in fermentation are examined. Energy and water consumption data collected from different Cargill fermentation plants, i.e., ethanol, lactic acid, and 2-keto-L-gulonic acid, confirm that improvements in fermentation titer play a decisive role in downstream economics and environmental footprint.

An aminoacylase activity from Streptomyces ambofaciens catalyzes the acylation of lysine on α-position and peptides on N-terminal position

The presence of aminoacylase activities was investigated in a crude extract of Streptomyces ambofaciens ATCC23877. First activities catalyzing the hydrolysis of N-α or ε-acetyl-L-lysine were identified. Furthermore, the acylation of lysine and different peptides was studied and compared with results obtained with lipase B of Candida antarctica (CALB). Different regioselectivities were demonstrated for the two classes of enzymes. CALB was able to catalyze acylation only on the ε-position whereas the crude extract from S. ambofaciens possessed the rare ability to catalyze the N-acylation on the α-position of the lysine or of the amino-acid in N-terminal position of peptides. Two genes, SAM23877_1485 and SAM23877_1734, were identified in the genome of Streptomyces ambofaciens ATCC23877 whose products show similarities with the previously identified aminoacylases from Streptomyces mobaraensis. The proteins encoded by these two genes were responsible for the major aminoacylase hydrolytic activities. Furthermore, we show that the hydrolysis of N-α-acetyl-L-lysine could be attributed to the product of SAM23877_1734 gene.

Alteration of substrate selection of antibiotic acylase from β-lactam to echinocandin

The antibiotic acylases belonging to the N-terminal nucleophile hydrolase superfamily are key enzymes for the industrial production of antibiotic drugs. Cephalosporin acylase (CA) and penicillin G acylase (PGA) are two of the most intensively studied enzymes that catalyze the deacylation of β-lactam antibiotics. On the other hand, aculeacin A acylase (AAC) is known to be an alternative acylase class catalyzing the deacylation of echinocandin or cyclic lipopeptide antibiotic compounds, but its structural and enzymatic properties remain to be explored. In the present study, 3D homology models of AAC were constructed, and docking simulation with substrate ligands was performed for AAC, as well as for CA and PGA. The docking models of AAC with aculeacin A suggest that AAC has the deep narrow binding pocket for the long-chain fatty acyl group of the echinocandin molecule. To confirm this, CA mutants have been designed to form the binding pocket for the long acyl chain. Experimentally synthesized mutant enzymes exhibited lower enzymatic activity for cephalosporin but higher activity for aculeacin A, in comparison with the wild-type enzyme. The present results have clarified the difference in mechanisms of substrate selection between the β-lactam and echinocandin acylases and demonstrate the usefulness of the computational approaches for engineering the enzymatic properties of antibiotic acylases.

Echinocandins: production and applications

The first echinocandin-type antimycotic (echinocandin B) was discovered in the 1970s. It was followed by the isolation of more than 20 natural echinocandins. These cyclic lipo-hexapeptides are biosynthesized on non-ribosomal peptide synthase complexes by different ascomycota fungi. They have a unique mechanism of action; as non-competitive inhibitors of β-1,3-glucan synthase complex they target the fungal cell wall. Results of the structure-activity relationship experiments let us develop semisynthetic derivatives with improved properties. Three cyclic lipohiexapeptides (caspofungin, micafungin and anidulafungin) are currently approved for use in clinics. As they show good fungicidal (Candida spp.) or fungistatic (Aspergillus spp.) activity against the most important human pathogenic fungi including azole-resistant strains, they are an important addition to the antifungal armamentarium. Some evidence of acquired resistance against echinocandins has been detected among Candida glabrata strains in recent years, which enhanced the importance of data collected on the mechanism of acquired resistance developing against the echinocandins. In this review, we show the structural diversity of natural echinocandins, and we summarize the emerging data on their mode of action, biosynthesis and industrial production. Their clinical significance as well as the mechanism of natural and acquired resistance is also discussed.