Candida albicans SUR7 contributes to secretion, biofilm formation, and macrophage killing

BMC Microbiology, Apr 2010

Background Candida albicans SUR7 has been shown to be required for plasma membrane organization and cell wall synthesis, but its role in virulence is not known. Using a bioinformatics strategy, we previously identified several novel putative secretion pathway proteins potentially involved in virulence, including the C. albicans homolog of the Saccharomyces cerevisiae endocytosis-related protein Sur7p. We therefore generated a C. albicans sur7Δ null mutant and examined its contribution to key virulence attributes. Results Structurally, the C. albicans sur7Δ mutant was impaired in response to filamentation-inducing conditions, and formed aberrant hyphae with extensive accumulation of plasma membrane-derived structures within the cell. Absence of SUR7 resulted in a temperature-sensitive growth defect at high temperatures (42°C), which was partially rescued by addition of NaCl. We next examined the role of the SUR7 paralog C. albicans FMP45 in this temperature-sensitive phenotype. Analysis of C. albicans Fmp45p-GFP demonstrated co-localization of Fmp45p with Sur7p and increased fluorescence in the plasma membrane in the presence of high salt. We next focused on key virulence-related phenotypes. The C. albicans sur7Δ null mutant exhibited secretory defects: reduced lipase secretion, and increased levels of secreted Sap2p. The null mutant was hyper-susceptible to sub-inhibitory concentrations of caspofungin, but not amphotericin B and 5-fluorocytosine. Functionally, the sur7Δ mutant demonstrated increased adhesion to polystyrene and of note, was markedly defective in biofilm formation. In an in vitro macrophage model of virulence, the sur7Δ mutant was impaired in macrophage killing. Conclusions Plasma membrane and cell wall organization are important for cell morphology, and alterations of these structures contributed to impairment of several key virulence-associated phenotypes in the C. albicans sur7Δ mutant.

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Candida albicans SUR7 contributes to secretion, biofilm formation, and macrophage killing

BMC Microbiology RCeaseanrcdhairdticale albicans SUR7 contributes to secretion, biofilm formation, and macrophage killing Stella M Bernardo 0 1 Samuel A Lee 0 1 0 Section of Infectious Diseases, New Mexico Veterans Healthcare System , Albuquerque, NM , USA 1 Division of Infectious Diseases, Department of Medicine, University of New Mexico Health Science Center , Albuquerque, NM , USA Background: Candida albicans SUR7 has been shown to be required for plasma membrane organization and cell wall synthesis, but its role in virulence is not known. Using a bioinformatics strategy, we previously identified several novel putative secretion pathway proteins potentially involved in virulence, including the C. albicans homolog of the Saccharomyces cerevisiae endocytosis-related protein Sur7p. We therefore generated a C. albicans sur7 null mutant and examined its contribution to key virulence attributes. Results: Structurally, the C. albicans sur7 mutant was impaired in response to filamentation-inducing conditions, and formed aberrant hyphae with extensive accumulation of plasma membrane-derived structures within the cell. Absence of SUR7 resulted in a temperature-sensitive growth defect at high temperatures (42C), which was partially rescued by addition of NaCl. We next examined the role of the SUR7 paralog C. albicans FMP45 in this temperaturesensitive phenotype. Analysis of C. albicans Fmp45p-GFP demonstrated co-localization of Fmp45p with Sur7p and increased fluorescence in the plasma membrane in the presence of high salt. We next focused on key virulence-related phenotypes. The C. albicans sur7 null mutant exhibited secretory defects: reduced lipase secretion, and increased levels of secreted Sap2p. The null mutant was hyper-susceptible to sub-inhibitory concentrations of caspofungin, but not amphotericin B and 5-fluorocytosine. Functionally, the sur7 mutant demonstrated increased adhesion to polystyrene and of note, was markedly defective in biofilm formation. In an in vitro macrophage model of virulence, the sur7 mutant was impaired in macrophage killing. Conclusions: Plasma membrane and cell wall organization are important for cell morphology, and alterations of these structures contributed to impairment of several key virulence-associated phenotypes in the C. albicans sur7 mutant. - Background C. albicans SUR7 shares 44% identity and 65% similarity with S. cerevisiae SUR7. S. cerevisiae SUR7 encodes a predicted integral membrane protein with an N-terminal signal sequence and four transmembrane domains, and is a member of a family of proteins that also includes Yn1194p, Ydl222p, and Ylr414cp [1,2]. Sur7p localizes to large, immobile, stable cortical patches on the plasma membrane, termed "eisosomes" which mark sites of endocytosis [3,4]. Deletion of S. cerevisiae SUR7 resulted in a strain with a defect in sporulation and altered plasma membrane sphingolipid content [4]. Alvarez and Konopka [5] identified C. albicans Sur7p in a detergent-resistant fraction of the plasma membrane in a proteomics study on N-acetylglucosamine-induced proteins. Recently, they generated a C. albicans sur7 knockout mutant which is characterized by aberrant cell wall organization [2]. Specifically, lack of SUR7 in C. albicans results in mislocalization of actin and septin, and abnormal cell wall material protruding into and forming structures within the cytoplasm. However, from a phenotypic standpoint, little is known regarding the role of C. albicans SUR7 in pathogenesis. A number of C. albicans virulence-related secreted proteins that remain associated with the plasma membrane or cell wall have been identified, including the outer mannoprotein Hwp1p [6], adhesins encoded by the ALS family of genes [7], and membrane proteins encoded by the pH-responsive genes PHR1 and PHR2 [8-11]. However, a genome-wide understanding of Candida secretory pathway proteins and virulence is still limited. Previously, we took advantage of SignalP v2.0 [12,13] and a series of additional validated predictive algorithms to define a computational secretome of C. albicans from its entire genome [14]. In addition to identifying putative soluble secretory proteins, we also identified a number of putative and known membrane and cell-wall associated proteins [14]. We next compared these databases with published genome-wide expression profiling data to identify candidate virulence-related genes. Fradin et al. [15] performed genomic expression profiling in C. albicans exposed in vitro to blood and in vivo during infection in a standard mouse model of disseminated candidiasis and identified groups of genes highly expressed under these conditions. When compared with the dataset of predicted secretion pathway ORFs, a number of virulencerelated genes were concordant, including Hwp1p and the Als family of adhesins [6,7], Phr1p [8], Sap9p [16], Sod5p [17,18], and Sun41p [19-21]. Thus, we identified known soluble secreted and membrane-associated secretion pathway (...truncated)


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Stella M Bernardo, Samuel A Lee. Candida albicans SUR7 contributes to secretion, biofilm formation, and macrophage killing, BMC Microbiology, 2010, pp. 133, 10, DOI: 10.1186/1471-2180-10-133