Molecular cloning of bovine eIF5A and deoxyhypusine synthase cDNA

Knockout of secondary alcohol dehydrogenase in Nocardia cholesterolicum NRRL 5767 by CRISPR/Cas9 genome editing technology

Nocardia cholesterolicum NRRL 5767 is well-known for its ability to convert oleic acid to 10-hydroxystearic acid (~88%, w/w) and 10-ketostearic acid (~11%, w/w). Conversion of oleic acid to 10-hydroxystearic acid and then to 10-ketostearic acid has been proposed to be catalyzed by oleate hydratase and secondary alcohol dehydrogenase, respectively. Hydroxy fatty acids are value-added with many industrial applications. The objective of this study was to improve the Nocardia cholesterolicum NRRL5767 strain by CRISPR/Cas9 genome editing technology to knockout the secondary alcohol dehydrogenase gene, thus blocking the conversion of 10-hydroxystearic acid to 10-ketostearic acid. The improved strain would produce 10-hydroxystearic acid solely from oleic acid. Such improvement would enhance the production of 10-hydroxystearic acid by eliminating downstream separation of 10-hydroxystearic acid from 10-ketostearic acid. Here, we report: (1) Molecular cloning and characterization of two functional recombinant oleate hydratase isozymes and a functional recombinant secondary alcohol dehydrogenase from Nocardia cholesterolicum NRRL5767. Existence of two oleate hydratase isozymes may explain the high conversion yield of 10-hydroxystearic acid from oleic acid. (2) Construction of a CRISPR/Cas9/sgRNA chimeric plasmid that specifically targeted the secondary alcohol dehydrogenase gene by Golden Gate Assembly. (3) Transformation of the chimeric plasmid into Nocardia cholesterolicum NRRL 5767 by electroporation and screening of secondary alcohol dehydrogenase knockout mutants. Two mutants were validated by their lack of secondary alcohol dehydrogenase activity at the protein level and mutation at the targeted 5’ coding region and the 5’ upstream at the DNA level. The knockout mutants offer improvements by converting added oleic acid to solely 10-hydroxystearic acid, thus eliminating downstream separation of 10-hydroxystearic acid from 10-ketostearic acid. To the best of our knowledge, we report the first successful knockout of a target gene in the Nocardia species using CRISPR/Cas9/sgRNA-mediated genome editing technology.

Molecular cloning and functional expression of bovine deoxyhypusine hydroxylase cDNA and homologs

Deoxyhypusine hydroxylase is the second of the two enzymes that catalyzes the maturation of eukaryotic initiation factor 5A (eIF5A). The mature eIF5A is the only known protein in eukaryotic cells that contains the unusual amino acid hypusine (N(epsilon)-(4-amino-2(R)-hydroxybutyl)lysine). Synthesis of hypusine is essential for the function of eIF5A in eukaryotic cell proliferation and survival. Here, we describe the cloning and characterization of bovine deoxyhypusine hydroxylase cDNA and its homologs. The deduced bovine deoxyhypusine hydroxylase protein is 87% identical to human enzyme and 45% identical to yeast enzyme. The overexpressed enzyme showed activity in catalyzing the hydroxylation of the deoxyhypusine residue in the eIF5A intermediate. An amino acid substitution from Glu 57 to Gly located at one of the four conserved His-Glu (HE) pairs, the potential metal coordination sites, resulted in severe reduction of deoxyhypusine hydroxylase activity. A deletion at the HEAT-repeats 1-3 resulted in complete losses of deoxyhypusine hydroxylase activity.

Higher activity of recombinant bovine deoxyhypusine synthase vs. human deoxyhypusine synthase

Mature eukaryotic initiation factor 5A (eIF5A) is the only known protein in eukaryotic cells that contains the unusual amino acid hypusine (Nepsilon-(4-amino-2(R)-hydroxybutyl)lysine). The synthesis of hypusine is essential for the function of eIF5A in eukaryotic cell proliferation and survival. Deoxyhypusine synthase is the first of the two enzymes that catalyzes the maturation of eIF5A. We have subcloned the cDNA encoding bovine and human deoxyhypusine synthase into a pET-11a expression vector, separately. T7-tagged bovine and human deoxyhypusine synthase have been overexpressed in Escherichia coli and purified to homogeneity using T7 antibody affinity chromatography. Activities of the enzyme from both human and bovine have been measured by their ability to convert the eIF5A precursor protein to the intermediate, deoxyhypusine form of eIF5A. Our results have shown that bovine deoxyhypusine synthase has considerably higher activity than human deoxyhypusine synthase in catalyzing the synthesis of deoxyhypusine.