Distinct enzymatic and cellular characteristics of two secretory phospholipases A2 in the filamentous fungus Aspergillus oryzae.

Microbial secretory phospholipases A(2) (sPLA(2)s) are among the last discovered and least known members of this functionally diverse family of enzymes. We analyzed here two sPLA(2)s, named sPlaA and sPlaB, of the filamentous ascomycete Aspergillus oryzae. sPlaA and sPlaB consist of 222 and 160 amino acids, respectively, and share the conserved Cys and catalytic His-Asp residues typical of microbial sPLA(2)s. Two sPLA(2)s differ in pH optimum, Ca(2+) requirement and expression profile. The splaA mRNA was strongly upregulated in response to carbon starvation, oxidative stress and during conidiation, while splaB was constitutively expressed at low levels and was weakly upregulated by heat shock. Experiments with sPLA(2) overexpressing strains demonstrated that two enzymes produce subtly different phospholipid composition variations and also differ in their subcellular localization: sPlaA is most abundant in hyphal tips and secreted to the medium, whereas sPlaB predominantly localizes to the ER-like intracellular compartment. Both sPLA(2) overexpressing strains were defective in conidiation, which was more pronounced for sPlaB overexpressors. Although no major morphological abnormality was detected in either DeltasplaA or DeltasplaB mutants, hyphal growth of DeltasplaB, but not that of DeltasplaA, displayed increased sensitivity to H(2)O(2) treatment. These data indicate that two A. oryzae sPLA(2) enzymes display distinct, presumably non-redundant, physiological functions.

A cytosolic phospholipase A2-like protein in the filamentous fungus Aspergillus oryzae localizes to the intramembrane space of the mitochondria.

In mammalian cells, cytosolic phospholipase A(2) (cPLA(2)) displays a variety of activities through the release of arachidonic acid in response to cellular stimuli. In this study, we characterize the putative cPLA(2)-like protein, AoPlaA, in the filamentous fungus Aspergillus oryzae. When AoPlaA-EGFP was expressed in A. oryzae, it localized to the tubular structures that was costained by the marker dye for the mitochondria. A biochemical fractionation experiment showed that AoPlaA was present in the mitochondria-enriched fraction. The presence of an N-terminal cleavable mitochondrial targeting signal in AoPlaA was demonstrated by N-terminal amino acid sequence analysis, and by showing that chimeric proteins consisting of N-terminal 65 or 50 amino acids of AoPlaA fused to enhanced green fluorescent protein (EGFP) localized to the mitochondria. Submitochondrial fractionation of AoPlaA expressed in Saccharomyces cerevisiae demonstrated that AoPlaA localizes to the intramembrane space of the mitochondria. Taken together, the results presented here demonstrate a novel, submitochondrial localization of the cPLA(2)-like protein in the filamentous fungi.