Cryptococcal phospholipases: a novel lysophospholipase discovered in the pathogenic fungus Cryptococcus gattii

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Abstract
The pathogenic fungus Cryptococcus neoformans produces an extracellular PLB1 (phospholipase B1), shown previously to be a virulence factor. A novel phospholipase (LPL1) with only LPL (lysophospholipase) and LPTA (transacylase) activities has now been characterized in C. gattii, and found to be a 66-kDa glycoprotein (by SDS/PAGE), with a native molecular mass of 670 kDa. The pI was 6.3, and it was active at high temperatures (to 70 degrees C), as well as at both acidic and neutral pH values. It was stimulated by calcium and palmitoyl carnitine at pH 7.0, but not at pH 5.0, and palmitoyl lysophosphatidylcholine was the preferred substrate. Sequencing indicated that LPL1 is a novel cryptococcal lysophospholipase, and not the gene product of CnLYSO1 or PLB1. A protein with only LPL and LPTA activities was subsequently isolated from two strains of C. neoformans var. grubii. A PLB1 enzyme was isolated from both C. gattii and a highly virulent strain of C. neoformans var. grubii (H99). In both cases, all three enzyme activities (PLB, LPL and LPTA) were present in one 95-120 kDa glycoprotein (by SDS/PAGE) with pI 3.9-4.3. Characterization of PLB1 from C. gattii showed that it differed from that of C. neoformans in its larger native mass (275 kDa), high PLB activity relative to LPL and LPTA, and preference for saturated lipid substrates. Differences in the properties between the secreted phospholipases of the two cryptococcal species could contribute to phenotypic differences that determine their respective environmental niches and different clinical manifestations.