Identification of a species-specific aminotransferase in Pediococcus acidilactici capable of forming \u03b1-aminobutyrate

Alexander Wenger,Stefan Irmler,Remo S Schmidt,Reto Portmann,Elisabeth Eugster,Laure Weisskopf,Alexandra Roetschi

doi:10.1186/s13568-020-01034-2

Alexander Wenger, Stefan Irmler + Show 5 more

Open Access

https://doi.org/10.1186/s13568-020-01034-2

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Abstract

During cheese ripening, the bacterial strain Pediococcus acidilactici FAM18098 produces the non-proteinogenic amino acid, α-aminobutyrate (AABA). The metabolic processes that lead to the biosynthesis of this compound are unknown. In this study, 10 P. acidilactici, including FAM18098 and nine Pediococcus pentosaceus strains, were screened for their ability to produce AABA. All P. acidilactici strains produced AABA, whereas the P. pentosaceus strains did not. The genomes of the pediococcal strains were sequenced and searched for genes encoding aminotransferases to test the hypothesis that AABA could result from the transamination of α-ketobutyrate. A GenBank and KEGG database search revealed the presence of a species-specific aminotransferase in P. acidilactici. The gene was cloned and its gene product was produced as a His-tagged fusion protein in Escherichia coli to determine the substrate specificity of this enzyme. The purified recombinant protein showed aminotransferase activity at pH 5.5. It catalyzed the transfer of the amino group from leucine, methionine, AABA, alanine, cysteine, and phenylalanine to the amino group acceptor α-ketoglutarate. Αlpha-ketobutyrate could replace α-ketoglutarate as an amino group acceptor. In this case, AABA was produced at significantly higher levels than glutamate. The results of this study show that P. acidilactici possesses a novel aminotransferase that might play a role in cheese biochemistry and has the potential to be used in biotechnological processes for the production of AABA.

Highlights

IntroductionIn a series of degradation steps, the proteins are broken down into amino acids
During cheese ripening, proteolysis of the caseins occurs
Pediococcus acidilactici produces the non‐proteinogenic amino acids, AABA and ornithine Pediococcus acidilactici FAM18098 and nine other P. acidilactici strains (Table 1) were incubated in a broth in which AABA formation can be detected to test if AABA formation was strain- or species-specific

Summary

Introduction

In a series of degradation steps, the proteins are broken down into amino acids. Thereby, lactic acid bacteria (LAB) play an important role as they use the free amino acids for energy production, regulation of the internal pH, regeneration of co-substrates, and protein biosynthesis (Ardö 2006). It was shown that Pediococcus acidilactici FAM18098 catabolized serine and threonine and formed α-aminobutyrate (AABA) and alanine in vitro and in cheese (Irmler et al 2013; Eugster et al 2019). The formation of the non-proteinogenic amino acid, AABA, is quite unusual, and the enzymes involved in the anabolism of this substance are unknown.

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