Phospholipase A2 and phospholipase B activities in fungi

Abstract

As saprophytes or disease causing microorganisms, fungi acquire nutrients from dead organic material or living host organisms. Lipids as structural components of cell membranes and storage compartments play an important role as energy-rich food source. In recent years, it also has become clear that lipids have a wide range of bioactive properties including signal transduction and cell to cell communication. Thus, it is not surprising that fungi possess a broad range of hydrolytic enzymes that attack neutral lipids and phospholipids. Especially during infection of a mammalian host, phospholipase A(2) (PLA(2)) enzymes released by fungi could play important roles not only for nutrient acquisition and tissue invasion, but for intricate modulation of the host's immune response. Sequencing of fungal genomes has revealed a wide range of genes encoding PLA(2) activities in fungi. We are just beginning to become aware of the significance these enzymes could have for the fungal cells and their interaction with the host.

Figure 1. Mechanism of action of phospholipases (A, B, C, D)

The positions of hydrolytic activities of different types of phospholipases on a phospholipid (PAPC) are depicted. PLA₂ or PLB enzymes form lysophospholipids whose remaining esterified fatty acid can be removed by PLBs or other lysophospholipases. Lysophospholipase/transacylase (LPTA) activity commonly found in PLBs may esterify a free fatty acid (FFA) to a lysophospholipid resulting in a phospholipid. Arachidonic acid (AA) in the sn-2 position of PAPC can be mobilized by PLA₂ or PLB enzymes and function as a precursor for eicosanoids which are generated by the indicated enzymatic activities.

Figure 2. Domain structure of PLA₂ enzymes

Putative fungal orthologues of secretory (sPLA₂) and cytosolic PLA₂ (cPLA₂) enzymes are shown in comparison to the human enzymes are shown. Additionally, the structural domains of fungal PLB enzymes and patatin-like phospholipases are depicted.