Identification and study of a Candida albicans protein homologous to Saccharomyces cerevisiae Ssr1p, an internal cell-wall protein

Abstract

After screening of a Candida albicans genome database, the product of an ORF (IPF 3054) that has 62 % homology with Saccharomyces cerevisiae Ssr1p, an internal cell-wall protein, was identified and named CaSsr1p. The deduced amino acid sequence shows that CaSsr1p contains an N-terminal hydrophobic signal peptide, is rich in Ser and Thr amino acids and has a potential glycosylphosphatidylinositol-attachment signal. CaSsr1p is released following degradation of isolated cell walls by zymolyase (mainly a 1,3-b-glucanase) and therefore seems to be covalently linked to the b-glucan of the cell walls. Both disruption and overexpression of the CaSSR1 gene caused an increased sensitivity to calcofluor white, Congo red and zymolyase digestion. These results suggest that CaSsr1p has a structural role associated with the cell-wall b-glucan. INTRODUCTIONCandida albicans is an opportunistic pathogenic fungus in humans which can cause either septicaemic or mucosal infections (Odds, 1988(Odds, , 1994. The number of fungal infections caused by C. albicans has increased dramatically in the last few decades, due to the rise in the number of immunocompromised patients and their life expectancies (Fox, 1993). C. albicans is a dimorphic organism capable of reproducing by budding (yeast cells) or by producing germ tubes (mycelial cells) depending upon environmental factors (Odds, 1988); this morphological transition has been associated with pathogenicity (Calderone & Braun, 1991;Odds, 1988;Sentandreu et al., 1993). Because the cell wall of C. albicans is the fungal structure responsible for the initial interaction with the host and for the characteristic shape of each growth form, several studies have focused on its biosynthesis and function (Gozalbo et al., 1994;Sentandreu et al., 1993;Valentin et al., 2000).The cell wall of C. albicans is a complex biochemical entity composed mainly of three components, namely, glucans (1,3-b-and 1,6-b-glucan), mannoproteins and chitin (Fleet, 1991;Valentin et al., 2000). The b-glucans are the main components, accounting for 50-60 % by weight of the cell wall in C. albicans and other fungi. Chitin, a linear polymer of 1,4-b-linked N-acetylglucosamine units, is a relatively minor (1-10 %) but important constituent. In most fungi, b-glucans and chitin polymers account for the rigidity of the cell wall as well as its morphology . Mannoproteins represent 30-40 % of the total cell wall and determine the surface properties, enabling C. albicans cells to interact and adhere to host tissues (Chaffin et al., 1998).Cell-wall mannoproteins can be divided into three groups according to the methods used for their extraction. One group can be solubilized by detergents, such as SDS, or chaotropic agents, such as urea, and is formed by mannoproteins loosely associated with other components of the cell wall (Elorza et al., 1985;Valentin et al., 1984). The second group can be extracted by reducing agents, DTT or b-mercaptoethanol (Casanova et al., 1989;Orlean et al., 1986). The third group can be released from the ce...

Candida albicansCell Wall Proteins

“…In their analyses, they listed 115 putative GPI-CWP class proteins (see Table 1 in the work of Richard and Plaine [312]); 70 were common to all three reports, 6 were found in common between the analyses of de Groot et al (74) and Eisenhaber et al (92). The remaining proteins were unique to one of the studies: 24 proteins from the study of de Groot et al (74), 9 from the study of Eisenhaber et al (92), and 6 from the study of Garcerá et al (118). GPI anchors may target proteins to the membrane or the cell wall.…”

“…Several studies have reported analyses of the C. albicans genome for proteins included in the GPI-CWP class (1,74,92,118,371). These proteins have been recently reviewed by Richard and Plaine (312), who focused on the three reports that used C. albicans genome assembly 19 (74,92,118).…”

“…Several studies have reported analyses of the C. albicans genome for proteins included in the GPI-CWP class (1,74,92,118,371). These proteins have been recently reviewed by Richard and Plaine (312), who focused on the three reports that used C. albicans genome assembly 19 (74,92,118). In their analyses, they listed 115 putative GPI-CWP class proteins (see Table 1 in the work of Richard and Plaine [312]); 70 were common to all three reports, 6 were found in common between the analyses of de Groot et al (74) and Eisenhaber et al (92).…”

Comprehensive Analysis of Glycosylphosphatidylinositol-Anchored Proteins in Candida albicans

“…Four different lists of C. albicans GpiPs are published in the literature (12,16,21,55). In this review, we will not include the results of Paula Sundstrom's analysis since her work was done using assembly 6, an incomplete genome sequence.…”

“…In this review, we will not include the results of Paula Sundstrom's analysis since her work was done using assembly 6, an incomplete genome sequence. In an attempt to simplify our analysis, we have made a comprehensive list of putative GpiPs by combining the three data sets identified from assembly 19 (12,16,21). The three different teams presenting lists of C. albicans GpiPs identified different numbers of putative GpiPs (102, 104, and 169), but a careful analysis of each data set allowed us to refine our list (Table 1).…”