Amino Acid Catabolism by an areA -Regulated Gene Encoding an l -Amino Acid Oxidase with Broad Substrate Specificity in Aspergillus nidulans

Abstract

The filamentous fungus Aspergillus nidulans can use a wide range of compounds as nitrogen sources. The synthesis of the various catabolic enzymes needed to breakdown these nitrogen sources is regulated by the areA gene, which encodes a GATA transcription factor required to activate gene expression under nitrogen-limiting conditions. The areA102 mutation results in pleiotropic effects on nitrogen source utilization, including better growth on certain amino acids as nitrogen sources. Mutations in the sarA gene were previously isolated as suppressors of the strong growth of an areA102 strain on L-histidine as a sole nitrogen source. We cloned the sarA gene by complementation of a sarA mutant and showed that it encodes an L-amino acid oxidase enzyme with broad substrate specificity. Elevated expression of this enzyme activity in an areA102 background accounts for the strong growth of these strains on amino acids that are substrates for this enzyme. Loss of function sarA mutations, which abolish the L-amino acid oxidase activity, reverse the areA102 phenotype. Growth tests with areA102 and sarA mutants show that this enzyme is the primary route of catabolism for some amino acids, while other amino acids are metabolized through alternative pathways that yield either ammonium or glutamate for growth.

l-Amino acid oxidase of the fungus Hebeloma cylindrosporum displays substrate preference towards glutamate

“…Lao1 protein sequences of H. cylindrosporum and L. bicolor displayed low global identities compared with several other characterized Lao-sequences, including those from the basidiomycete A. phalloides and two ascomycete fungi (Davis et al, 2005;Niedermann & Lerch, 1990;Stasyk et al, 2010). Similarly, phylogenetic analyses have previously shown that large evolutionary distances separated the Lao sequences from ascomycetes, snakes, bacteria and algae (Macheroux et al, 2001).…”

Regulatory Genes Controlling Fatty Acid Catabolism and Peroxisomal Functions in the Filamentous Fungus Aspergillus nidulans

“…Standard methods for DNA manipulations, RNA isolation, nucleic acid blotting, and hybridization have been described previously (12,60,75). The sequences of oligonucleotides used are given in Table 1.…”

Lysine enhances the effect of amphotericin B against <italic>Candida albicans in vitro</italic>

“…The generation of hydrogen peroxide confers antimicrobial and antitumoral properties to LAO [35,36]. It has been proposed that fungal LAO is involved in the utilization of amino acids as a nitrogen source [37,38]. Recently, Tong et al [39] reported that LAO could be used by the lactic acid bacterium Streptococcus oligofermentans to generate hydrogen peroxide, which is involved in the process of microbial competition with the cariogenic Streptococcus mutans.…”