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A proposed mechanism for the interaction between the Candida albicans Als3 adhesin and streptococcal cell wall proteins.

Hoyer LL, Oh SH, Jones R, Cota E - Front Microbiol (2014)

Bottom Line: C. albicans displaying Als3 PBC mutant proteins showed significantly reduced binding to S. gordonii; mutation of the AFR did not affect the interaction.These observations present an enigma: the Als PBC binds free C termini of ligands, but the SspB C terminus is covalently linked to peptidoglycan and thus unavailable as a ligand.These observations and the predicted SspB elongated structure suggest that partial proteolysis of streptococcal cell wall proteins is necessary for recognition by Als adhesins.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathobiology, University of Illinois at Urbana-Champaign Urbana, IL, USA.

ABSTRACT
C. albicans binds various bacteria, including the oral commensal Streptococcus gordonii. Published reports documented the role of C. albicans Als3 and S. gordonii SspB in this interaction, and the importance of the Als N-terminal domain (NT-Als) in C. albicans adhesion. Here, we demonstrate that Als1 also binds S. gordonii. We also describe use of the NT-Als crystal structure to design mutations that precisely disrupt peptide-binding cavity (PBC) or amyloid-forming region (AFR) function in Als3. C. albicans displaying Als3 PBC mutant proteins showed significantly reduced binding to S. gordonii; mutation of the AFR did not affect the interaction. These observations present an enigma: the Als PBC binds free C termini of ligands, but the SspB C terminus is covalently linked to peptidoglycan and thus unavailable as a ligand. These observations and the predicted SspB elongated structure suggest that partial proteolysis of streptococcal cell wall proteins is necessary for recognition by Als adhesins.

No MeSH data available.


Related in: MedlinePlus

S. gordonii co-aggregation with C. albicans strains lacking Als1, Als3 or both proteins. (A) The co-aggregation assay was conducted and analyzed as described above. William Fonzi, Georgetown University, provided C. albicans control strain CAI12 (ALS1/ALS1 ALS3/ALS3; Porta et al., 1999). Aaron Mitchell, Carnegie Mellon University, provided strains DAY185 (ALS1/ALS1 ALS3/ALS3; Nobile et al., 2008), Δals1 Δals3 (CJN1348; als1/als1 als3/als3; Nobile et al., 2008), Als1 Δals3 (CJN1352; als1/als1::ALS1 als3/als3; Nobile et al., 2008), and Δals1 Als3 (CJN1356; als1/als1 als3/als3::ALS3; Nobile et al., 2008). All assays used S. gordonii strain SspB. The full set of comparisons between means is provided as Table 2 in Supplementary Material. (B)C. albicans hyphae were grown for 90 min, then immunolabeled with a monoclonal antibody that recognizes either Als1 (Coleman et al., 2010) or Als3 (antibody 3-A5; Coleman et al., 2009). Genotypes of each strain are shown below the images. (C)C. albicans hyphae were grown for 90 min and immunolabeled with a monoclonal antibody that recognizes either Als2 or Als4 (Coleman et al., 2012). Methods for immunolabeling of C. albicans germ tubes and for fluorescence microscopy and image processing were published previously (Coleman et al., 2009).
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Figure 2: S. gordonii co-aggregation with C. albicans strains lacking Als1, Als3 or both proteins. (A) The co-aggregation assay was conducted and analyzed as described above. William Fonzi, Georgetown University, provided C. albicans control strain CAI12 (ALS1/ALS1 ALS3/ALS3; Porta et al., 1999). Aaron Mitchell, Carnegie Mellon University, provided strains DAY185 (ALS1/ALS1 ALS3/ALS3; Nobile et al., 2008), Δals1 Δals3 (CJN1348; als1/als1 als3/als3; Nobile et al., 2008), Als1 Δals3 (CJN1352; als1/als1::ALS1 als3/als3; Nobile et al., 2008), and Δals1 Als3 (CJN1356; als1/als1 als3/als3::ALS3; Nobile et al., 2008). All assays used S. gordonii strain SspB. The full set of comparisons between means is provided as Table 2 in Supplementary Material. (B)C. albicans hyphae were grown for 90 min, then immunolabeled with a monoclonal antibody that recognizes either Als1 (Coleman et al., 2010) or Als3 (antibody 3-A5; Coleman et al., 2009). Genotypes of each strain are shown below the images. (C)C. albicans hyphae were grown for 90 min and immunolabeled with a monoclonal antibody that recognizes either Als2 or Als4 (Coleman et al., 2012). Methods for immunolabeling of C. albicans germ tubes and for fluorescence microscopy and image processing were published previously (Coleman et al., 2009).

Mentions: Initial experiments evaluated binding between wild-type and mutant C. albicans and S. gordonii strains. The interactions were quantified in categories based on the location and abundance of bacteria binding to germ tubes (Figure 1). Co-incubation of control C. albicans (Als3LA) and S. gordonii (SspB) strains showed significantly more C. albicans cells with high levels of bacterial adhesion (categories 4 and 5) than when either Als3 or SspB, or both, were absent (compare red bars to all other colors in Figure 1A in categories 4 and 5; P < 0.05). Similarly, co-incubation of Als3LA and SspB strains showed fewer category 0 cells than some of the other strain combinations (P < 0.0001 compared to Als3LA & ΔsspB and Δals3 & ΔsspB). Interestingly, there was no significant difference in category 0 cells for the combinations of Als3LA & SspB and Δals3 & SspB (P = 0.2), despite the lack of Als3 in the latter pair. Rather than occupying category 0, cells from the Δals3 & SspB combination tended to populate categories 1 and 2, which reflected S. gordonii binding to regions of the C. albicans germ tube with high abundance of other Als proteins including Als1, Als2, and Als4 (Coleman et al., 2010, 2012; Figure 2). Together, these data confirm the importance of Als3 and SspB in binding of S. gordonii to C. albicans, and also suggest the involvement of other Als proteins in the interaction.


A proposed mechanism for the interaction between the Candida albicans Als3 adhesin and streptococcal cell wall proteins.

Hoyer LL, Oh SH, Jones R, Cota E - Front Microbiol (2014)

S. gordonii co-aggregation with C. albicans strains lacking Als1, Als3 or both proteins. (A) The co-aggregation assay was conducted and analyzed as described above. William Fonzi, Georgetown University, provided C. albicans control strain CAI12 (ALS1/ALS1 ALS3/ALS3; Porta et al., 1999). Aaron Mitchell, Carnegie Mellon University, provided strains DAY185 (ALS1/ALS1 ALS3/ALS3; Nobile et al., 2008), Δals1 Δals3 (CJN1348; als1/als1 als3/als3; Nobile et al., 2008), Als1 Δals3 (CJN1352; als1/als1::ALS1 als3/als3; Nobile et al., 2008), and Δals1 Als3 (CJN1356; als1/als1 als3/als3::ALS3; Nobile et al., 2008). All assays used S. gordonii strain SspB. The full set of comparisons between means is provided as Table 2 in Supplementary Material. (B)C. albicans hyphae were grown for 90 min, then immunolabeled with a monoclonal antibody that recognizes either Als1 (Coleman et al., 2010) or Als3 (antibody 3-A5; Coleman et al., 2009). Genotypes of each strain are shown below the images. (C)C. albicans hyphae were grown for 90 min and immunolabeled with a monoclonal antibody that recognizes either Als2 or Als4 (Coleman et al., 2012). Methods for immunolabeling of C. albicans germ tubes and for fluorescence microscopy and image processing were published previously (Coleman et al., 2009).
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Figure 2: S. gordonii co-aggregation with C. albicans strains lacking Als1, Als3 or both proteins. (A) The co-aggregation assay was conducted and analyzed as described above. William Fonzi, Georgetown University, provided C. albicans control strain CAI12 (ALS1/ALS1 ALS3/ALS3; Porta et al., 1999). Aaron Mitchell, Carnegie Mellon University, provided strains DAY185 (ALS1/ALS1 ALS3/ALS3; Nobile et al., 2008), Δals1 Δals3 (CJN1348; als1/als1 als3/als3; Nobile et al., 2008), Als1 Δals3 (CJN1352; als1/als1::ALS1 als3/als3; Nobile et al., 2008), and Δals1 Als3 (CJN1356; als1/als1 als3/als3::ALS3; Nobile et al., 2008). All assays used S. gordonii strain SspB. The full set of comparisons between means is provided as Table 2 in Supplementary Material. (B)C. albicans hyphae were grown for 90 min, then immunolabeled with a monoclonal antibody that recognizes either Als1 (Coleman et al., 2010) or Als3 (antibody 3-A5; Coleman et al., 2009). Genotypes of each strain are shown below the images. (C)C. albicans hyphae were grown for 90 min and immunolabeled with a monoclonal antibody that recognizes either Als2 or Als4 (Coleman et al., 2012). Methods for immunolabeling of C. albicans germ tubes and for fluorescence microscopy and image processing were published previously (Coleman et al., 2009).
Mentions: Initial experiments evaluated binding between wild-type and mutant C. albicans and S. gordonii strains. The interactions were quantified in categories based on the location and abundance of bacteria binding to germ tubes (Figure 1). Co-incubation of control C. albicans (Als3LA) and S. gordonii (SspB) strains showed significantly more C. albicans cells with high levels of bacterial adhesion (categories 4 and 5) than when either Als3 or SspB, or both, were absent (compare red bars to all other colors in Figure 1A in categories 4 and 5; P < 0.05). Similarly, co-incubation of Als3LA and SspB strains showed fewer category 0 cells than some of the other strain combinations (P < 0.0001 compared to Als3LA & ΔsspB and Δals3 & ΔsspB). Interestingly, there was no significant difference in category 0 cells for the combinations of Als3LA & SspB and Δals3 & SspB (P = 0.2), despite the lack of Als3 in the latter pair. Rather than occupying category 0, cells from the Δals3 & SspB combination tended to populate categories 1 and 2, which reflected S. gordonii binding to regions of the C. albicans germ tube with high abundance of other Als proteins including Als1, Als2, and Als4 (Coleman et al., 2010, 2012; Figure 2). Together, these data confirm the importance of Als3 and SspB in binding of S. gordonii to C. albicans, and also suggest the involvement of other Als proteins in the interaction.

Bottom Line: C. albicans displaying Als3 PBC mutant proteins showed significantly reduced binding to S. gordonii; mutation of the AFR did not affect the interaction.These observations present an enigma: the Als PBC binds free C termini of ligands, but the SspB C terminus is covalently linked to peptidoglycan and thus unavailable as a ligand.These observations and the predicted SspB elongated structure suggest that partial proteolysis of streptococcal cell wall proteins is necessary for recognition by Als adhesins.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathobiology, University of Illinois at Urbana-Champaign Urbana, IL, USA.

ABSTRACT
C. albicans binds various bacteria, including the oral commensal Streptococcus gordonii. Published reports documented the role of C. albicans Als3 and S. gordonii SspB in this interaction, and the importance of the Als N-terminal domain (NT-Als) in C. albicans adhesion. Here, we demonstrate that Als1 also binds S. gordonii. We also describe use of the NT-Als crystal structure to design mutations that precisely disrupt peptide-binding cavity (PBC) or amyloid-forming region (AFR) function in Als3. C. albicans displaying Als3 PBC mutant proteins showed significantly reduced binding to S. gordonii; mutation of the AFR did not affect the interaction. These observations present an enigma: the Als PBC binds free C termini of ligands, but the SspB C terminus is covalently linked to peptidoglycan and thus unavailable as a ligand. These observations and the predicted SspB elongated structure suggest that partial proteolysis of streptococcal cell wall proteins is necessary for recognition by Als adhesins.

No MeSH data available.


Related in: MedlinePlus