Phosphatidylserine synthase and phosphatidylserine decarboxylase are essential for cell wall integrity and virulence in Candida albicans

Abstract

SummaryPhospholipid biosynthetic pathways play crucial roles in the virulence of several pathogens; however, little is known about how phospholipid synthesis affects pathogenesis in fungi such as Candida albicans. A C. albicans phosphatidylserine (PS) synthase mutant, cho1D/D, lacks PS, has decreased phosphatidylethanolamine (PE), and is avirulent in a mouse model of systemic candidiasis. The cho1D/D mutant exhibits defects in cell wall integrity, mitochondrial function, filamentous growth, and is auxotrophic for ethanolamine. PS is a precursor for de novo PE biosynthesis. A psd1D/D psd2D/D double mutant, which lacks the PS decarboxylase enzymes that convert PS to PE in the de novo pathway, has diminished PE levels like those of the cho1D/D mutant. The psd1D/D psd2D/D mutant exhibits phenotypes similar to those of the cho1D/D mutant; however, it is slightly more virulent and has less of a cell wall defect. The virulence losses exhibited by the cho1D/D and psd1D/D psd2D/D mutants appear to be related to their cell wall defects which are due to loss of de novo PE biosynthesis, but are exacerbated by loss of PS itself. Cho1p is conserved in fungi, but not mammals, so fungal PS synthase is a potential novel antifungal drug target.

Role of phosphatidylserine synthase in shaping the phospholipidome of Candida albicans

“…The reintegrant strains psd1 / ::PSD1 and psd2 / ::PSD2 also show slight increases in levels of PS. The psd1 / psd2 / mutant, which lacks all PS decarboxylase activity (Chen et al 2010a), has over a 3-fold increase in PS species overall, but individual species are overrepresented by 2-to 5-fold. The 34:n species, which were the most abundant in wild type, are also the most abundant in psd1 / psd2 / and are overrepresented by ∼5 fold compared to wild type.…”

“…Phospholipid profiles have previously been generated for the cho1 / , psd1 / and psd1 / psd2 / mutants using [ 32 P]-labeled phospholipids and thin layer chromatography (TLC) (Chen et al 2010b). However, TLC only reveals levels of different lipid classes (polar head groups).…”

“…The SC5314 (wild-type) strain of Candida albicans and mutants used in this study have been previously described by Chen et al (2010b). These include cho1 / (YLC337), cho1 / ::CHO1 (YLC344), psd1 / (YLC280), psd1 / ::PSD1 (YLC294), psd2 / (YLC271), psd2 / ::PSD2 (YLC290) and psd1 / psd2 / (YLC375).…”

“…Previous studies have identified the PS synthase (Cho1p) as a potential drug target in C. albicans (Braun et al 2005;Chen et al 2010b). Studies have been done on the enzymology and lipid profiles associated with PS synthase in Saccharomyces cerevisiae (BaeLee and Carman 1984), but little characterization of the orthologous enzyme or its effects on lipid profiles in C. albicans has been performed.…”

“…Although PI, PG and PS can be end products, PG and PS can be further modified to form CL and PE, respectively, and PE can subsequently be methylated to produce PC. Candida albicans also utilizes exogenously provided ethanolamine and choline to produce PE and PC, respectively, via the Kennedy pathway (Gibellini and Smith 2010;Chen et al 2010b;Henry, Kohlwein and Carman 2012).…”