Distinct enzymatic and cellular characteristics of two phospholipases A1 in Aspergillus oryzae

Abstract

Phospholipases A1 (PLA1s) catalyze the hydrolysis of sn-1 linkage in the glycerophospholipids, thereby releasing fatty acids and 2-acyl lysophospholipids. PLA1s are found in various organisms and tissues where they play diverse cellular functions, but their roles in filamentous fungi remain elusive. In this study we analyzed the enzymatic properties and physiological functions of two secretory PLA1s, PLA1-1 and its paralog PLA1-2, in the filamentous fungus Aspergillus oryzae. Although PLA1-1 and PLA1-2 share 49% amino acid sequence identity, they significantly differ in various aspects. While PLA1-1 displayed PLA1 activity to phosphatidylcholine and phosphatidylethanolamine, and degraded various phospholipids, PLA1-2 exhibited PLA1 activity only to phosphatidylglycerol. PLA1-1 was secreted to the culture medium, but PLA1-2 was not secreted and retained in the mycelium. Fluorescence microscopic observation of A. oryzae strains expressing EGFP-fused PLA1-1 and PLA1-2 demonstrated that they display overlapping but distinct cellular localization. A. oryzae mutants deleted for pla1-1 or pla1-2 grew normally, but the secreted phospholipase activity was significantly reduced in the Δpla1-1 strain. These data suggest that two sPLA1 enzymes are not redundant and play distinct cellular functions in A. oryzae.