Biology subjects

Wear, M. P.

Publications and source records attributed to Wear, M. P..

11 recordsLinked to original sources

bioRxiv2026

Calcium triggers Cryptococcus neoformans aggregation by forming coordination bonds with capsular glucuronoxylomannan

The cryptococcal polysaccharide capsule is a unique eukaryotic virulence factor that is a target for the immune system and the development of therapeutic antibodies. Our understanding of capsular architecture is limited to a few studies suggesting that metal dications play a role. In this work we explore a mechanism of cryptococcal aggregation that depends on calcium phosphate precipitation. We describe the chemical and biophysical properties of calcium interaction with the predominant cryptococcal polysaccharide, glucuronoxylomannan (GXM). We show that cell aggregation is a pH-dependent and occurs in a calcium dose-dependent manner. Furthermore, this cellular aggregation phenomenon as well as interpolymer capsular polysaccharide interactions are unique to calcium dications and do not occur with other mono- or dications as shown by size exclusion chromatography and circular dichroism. Diffusion ordered spectroscopy nuclear magnetic resonance and ab-initio calculations support complexation of calcium with glucuronic acid (GlcA). The ab-initio calculations also suggest that calcium ions can complex up to four GlcA monomers. Not only does calcium act as a scaffold for the cryptococcal capsule, interacting with up to four glucuronic acid residues of GXM, but calcium phosphate treatment of cells reduces the anti-phagocytic properties of the capsule, promoting ingestion by macrophages and altering antibody interactions with the capsule. This work advances our understanding of the cryptococcal capsule, its biophysical properties, by providing a model for the critical role of calcium interactions with capsular polymers of Cryptococcus neoformans including important impacts at the host-cell interface.

biochemistry↗

bioRxiv2025

Unexpected variability in laboratory and clinical assays used to quantify Cryptococcus neoformans polysaccharide.

The measurement of cryptococcal capsular polysaccharide (PS) amount and concentration is essential for laboratory studies of its structure and function. Clinically, the detection of cryptococcal capsular polysaccharide as cryptococcal antigen is a foundational assay for the diagnosis of cryptococcosis. In this study we compared the results of four laboratory assays for measuring cryptococcal polysaccharide (gravimetric determination, phenol-sulfuric acid reactivity, Size Exclusion Chromatography Multi-Angle Light Scattering (SEC-MALS), and ELISA) and two clinical assays (lateral flow assay (LFA) (IMMY) and the cryptococcal latex agglutination assay (CLAA) (Remel)) using four cryptococcal strains that each express single repeating polysaccharide motifs. The results show that the sensitivity of laboratory assays for PS was relatively consistent but manifested significant variation with strain. Phenol-sulfuric acid determination was highly variable unless the PS was pre-digested with HCl, suggesting that differences in the structural complexity of the polysaccharide could affect timing and intensity of the colorimetric reaction. Serological assays were the most sensitive, but these showed the most strain-to-strain variation on the threshold of PS detection consistent with antigenic differences. Differences in the reactivity of LFA and CLAA for cryptococcal PS from different strains imply that comparable cryptococcal antigen titers could reflect different concentrations of PS in bodily fluids. In summary, we find that variation in PS structure amongst strains can affect the sensitivity of the various tests used to measure cryptococcal PS. (Word count: 224)

microbiology↗

bioRxiv2025

Three annotated chromosome-level de novo genome assemblies of Lomentospora prolificans provide evidence for a chromosomal translocation event

Lomentospora prolificans is a fungal pathogen responsible for serious, often fatal, illness in patients with compromised immune systems. Treatment is rarely successful because L. prolificans is inherently resistant to all major classes of antifungal drugs. In this study we publish three chromosome-level de novo genome assemblies, including the first complete-level assembly of L. prolificans, along with genome annotations. The L. prolificans genome is packaged in 11 nuclear chromosomes and one mitochondrial chromosome, has 36.7-37.1 Mb, and encodes for a putative 7357-7640 genes. The length and composition of contigs in one stain varied from those of the other two strains, supporting the hypothesis that a chromosomal translocation took place. These assemblies were confirmed with pulsed-field gel electrophoresis. The availability of more complete genomes will hopefully help the search for new antifungal drugs and provides insights into the evolutionary history of this pathogenic fungus.

genomics↗

bioRxiv2024

On the relationship between serotype, chemotype and genotype for Cryptococcus spp. including a method for including polysaccharide structure in strain characterization

Over the past eight decades the classification of cryptococcal strains has relied on the technologies available to discriminate among isolates, such as serology, exopolysaccharide (EPS) NMR, and most recently multi-locus sequencing, which yielded serotypes, chemotypes, and genotypes, respectively. However, as one method superseded the other, the relationship between classification schemes became uncertain, resulting in assumptions that have not been rigorously validated. Here we compared the serotype, chemotype, and genotype as defined by multi-locus sequence typing (MLST) of 63 strains for which both serotype and chemotype characterization was available. None of the three strain typing methods were correlative with each other, although for about 50% of the strains there was correlation between chemotype and genotype. To address this, we updated the methodology of GXM motif categorization for cryptococcal strains through analyzing filter-isolated EPS by 1D [1H] NMR and assigning GXM motifs along with the O-acetylation level. The result is a facile method using minimally processed EPS material coupled with simple cryptococcal strain classification by GXM motif expression. While this method increases the correlation between MLST genotype and GXM motif expression, further studies to establish the polysaccharide regulatory genes in cryptococcus will be necessary to understand the polysaccharide differences. In summary, none of the current classification methods correlated with each other, indicating a dissociation between genotype and phenotype, which poses a challenge to the cryptococcal field for explaining how phenotypic characteristics arise and are maintained. Author SummaryThis work examines the relationship between methods of cryptococcal strain classification and the primary structure of the predominant polysaccharide glucuronoxylomannan (GXM). We find no strong correlation between the expression of trimannose repeat motifs of GXM by a strain and serotype, MLST genotype, or the previous polysaccharide classification system, chemotyping. With an understanding that none of these classification systems accurately represent the GXM sequences in cryptococcal polysaccharides, we describe a new, facile, rapid method of polysaccharide isolation and GXM motif expression characterization. Application of this method reveals a strong association between high levels of GXM O-acetylation, necessary for antibody binding, and the expression of a single motif of GXM. Additionally, the association between MLST genotype and GXM motif expression is higher when utilizing this new method. While much remains to be understood about this complex system, this work provides a new method to include GXM motif expression in cryptococcal strain expression allowing for more accurate strain descriptions in the future.

microbiology↗

bioRxiv2024

Proteins associated with Cryptococcus spp. extracellular polysaccharides are implicated in virulence, capsule integrity, and biofilm formation.

Cryptococcus neoformans and Cryptococcus gattii are pathogenic fungi comprising species complexes that are the etiological agents of cryptococcosis. Both fungal species complexes possess a variety of virulence factors that include a polysaccharide capsule, melanin production, enzymes, and the release of polysaccharides. In this study, we characterized the proteins associated with cryptococcal polysaccharides and analyzed their function by studying mutants deficient in their expression. Mass spectrometry analysis of exopolysaccharide fractions revealed 62 proteins, many of which were previously uncharacterized. Analysis of capsule size, structure, and integrity in protein-deficient mutants allowed us to identify four proteins, which we named Extracellular Polysaccharide Related proteins (Exa1-4), and whose absence affected proper capsule assembly and EPS release. In summary, cryptococcal exopolysaccharide is associated with proteins that are implicated in virulence, capsular integrity, and biofilm formation. Our results associated new phenotypes for four previously unknown genes and show that the filtered polysaccharide preparations are a rich source of proteins that can inform capsular assembly, virulence, and immunological studies.

molecular biology↗

bioRxiv2024

Semi-synthetic glycoconjugate vaccine candidate against Cryptococcus neoformans

Cryptococcus neoformans is a fungus classified by the World Health Organization as a critically important pathogen, posing a significant threat to immunocompromised individuals. In this study, we present the chemical synthesis and evaluation of two semi-synthetic vaccine candidates targeting the capsular polysaccharide glucuronoxylomannan (GXM) of C. neoformans. These semi-synthetic glycoconjugate vaccines contain the identical synthetic decasaccharide (M2 motif) antigen. This motif is present in serotype A strains, which constitute 95% of clinical cryptococcosis cases. This synthetic oligosaccharide was conjugated to two proteins (CRM197 and Anthrax 63 kDa PA) and tested for immunogenicity in mice. The conjugates elicited a specific antibody response that bound to the M2 motif but also exhibited additional cross-reactivity towards M1 and M4 GXM motifs. Both glycoconjugates produced antibodies that bound to GXM in ELISA assays and to live fungal cells. Mice immunized with the CRM197 glycoconjugate produced opsonic antibodies and displayed trends toward increased median survival relative to mice given a mock PBS injection (18 vs 15 days, p = 0.06). While these findings indicate promise, achieving a successful vaccine demands further optimization of the glycoconjugate. It could serve as a component in a multi-valent GXM motif vaccine, enhancing both strength and breadth of immune responses.

immunology↗

bioRxiv2023

The structure of a C. neoformans polysaccharide motif recognized by protective antibodies: a combined NMR and MD study

Cryptococcus neoformans is a fungal pathogen responsible for cryptococcosis and cryptococcal meningitis. The C. neoformans capsular polysaccharide and shed exopolysaccharide functions both as a key virulence factor and to protect the fungal cell from phagocytosis. Currently, a glycoconjugate of these polysaccharides is being explored as a vaccine to protect against C. neoformans infection. In this combined NMR and MD study, experimentally determined NOEs and J-couplings support a structure of the synthetic decasaccharide, GXM10-Ac3, obtained by MD. GXM10-Ac3 was designed as an extension of glucuronoxylomannan (GXM) polysaccharide motif (M2) which is common in the clinically predominant serotype A strains and is recognized by protective forms of GXM-specific monoclonal antibodies. The M2 motif is characterized by a 6-residue -mannan backbone repeating unit, consisting of a triad of -(1[->]3)-mannoses, modified by {beta}-(1[->]2)-xyloses on the first two mannoses and a {beta}-(1[->]2)-glucuronic acid on the third mannose. The combined NMR and MD analyses reveal that GXM10-Ac3 adopts an extended structure, with xylose/glucuronic acid branches alternating sides along the -mannan backbone. O-acetyl esters also alternate sides and are grouped in pairs. MD analysis of a twelve M2-repeating unit polymer supports the notion that the GXM10-Ac3 structure is uniformly represented throughout the polysaccharide. This experimentally consistent GXM model displays high flexibility while maintaining a structural identity, yielding new insights to further explore intermolecular interactions between polysaccharides, interactions with anti-GXM mAbs, and the cryptococcal polysaccharide architecture. Significance StatementThis study utilized a combined NMR and MD approach to elucidate the structure of a Cryptococcus neoformans GXM synthetic decasaccharide (GXM10-Ac3), recognized by protective anti-GXM mAbs. The data revealed an extended structure in which the xylose/glucuronic acid branches and pairs of 6-O-acetyl esters predominantly alternate sides along the -mannan backbone. MD analysis of a GXM polysaccharide predicts that the decasaccharide structure is uniformly represented in the polysaccharide. Additionally, the GXM exhibits high flexibility while maintaining structural identity. These findings lay the foundation for future studies aimed at understanding anti-GXM antibody-polysaccharide interactions.

biochemistry↗

bioRxiv2022

Lyophilization induces alterations in cryptococcal exopolysaccharide resulting in reduced antibody binding

The structural, antigenic, and immunological characterization of microbial polysaccharides requires purification that often involves detergent precipitation and lyophilization. Here we examine physicochemical changes induced by lyophilization on exopolysaccharide (EPS) of the pathogenic fungus Cryptococcus neoformans. Solution 1H NMR reveals significant anomeric signal attenuation following lyophilization of native EPS while 1H ssNMR shows few changes, suggesting diminished molecular motion and consequent broadening of 1H NMR polysaccharide resonances. 13C ssNMR, dynamic light scattering, and transmission electron microscopy show that, while native EPS has rigid molecular characteristics and contains small, loosely packed polysaccharide assemblies, lyophilized and resuspended EPS is disordered and contains larger dense rosette-like aggregates, suggesting that structural water molecules in the interior of the polysaccharide assemblies are removed during extensive lyophilization. Importantly, mAbs to C. neoformans polysaccharide binds the native EPS more strongly than lyophilized EPS. Together, these observations argue for caution when interpreting the biological and immunological attributes of polysaccharides that have been lyophilized to dryness.

microbiology↗

bioRxiv2021

Cryptococcus neoformans capsule regrowth experiments reveal dynamics of enlargement and architecture

The polysaccharide capsule of fungal pathogen Cryptococcus neoformans is a critical virulence factor that has historically evaded characterization. Polysaccharides remain attached to the cell as capsular polysaccharide (CPS) or are shed into the surroundings in the form of exopolysaccharide (EPS). While a great deal of study has been done examining the properties of EPS, far less is known about CPS. In this work, we detail the development of new physical and enzymatic methods for the isolation of CPS which can be used to explore the architecture of the capsule and removed capsular material. Sonication and glucanex digestion yield soluble CPS preparations, while French Press and modified glucanex digestion plus vortexing remove the capsule and cell wall producing polysaccharide aggregates that we call capsule ghosts. The existence of capsule ghosts implies an inherent organization that allows it to exist independent of the cell wall surface. As sonication and glucanex digestion were noncytotoxic, it was possible to observe the cryptococcal cells rebuilding their capsule, revealing new insights into capsule architecture and synthesis consistent with a model in which the capsule is assembled from smaller polymers, which are then assemble into larger ones. ImportanceCharacterization of the cryptococcal polysaccharide capsule relies on methods of isolation for its in vitro study. This study demonstrates that the capsule is susceptible to physical and enzymatic removal. The application of new methods yields insights into the anatomy, modular nature, and architecture of the capsule with both soluble CPS preparations and capsule ghosts. Together these insights inform on a long-standing debate modeling capsular assembly wherein our data shows that the capsule is assembled by smaller polymers added distally rather than by proximal addition or by polymers spanning the entire capsule radius.

microbiology↗

bioRxiv2021

Hinge Influences in Murine IgG Binding to Cryptococcus neoformans Capsule

Decades of studies on antibody structure led to the tenet that the V region binds antigens while the C region interacts with immune effectors. In some antibodies, however, the C region affects affinity and/or specificity for the antigen. One such case is that of the 3E5 antibodies, a family of monoclonal murine IgGs in which the mIgG3 isotype has different fine specificity to the Cryptococcus neoformans capsule polysaccharide than the other mIgG isotypes. Our group serendipitously found another pair of mIgG1/mIgG3 antibodies based on the 2H1 hybridoma to the C. neoformans capsule that recapitulated the differences observed with 3E5. In this work, we report the molecular basis of the constant domain effects on antigen binding using recombinant antibodies. As with 3E5, immunofluorescence experiments show a punctate pattern for 2H1-mIgG3 and an annular pattern for 2H1-mIgG1. Also as observed with 3E5, 2H1-mIgG3 bound on ELISA to both acetylated and non-acetylated capsular polysaccharide, whereas 2H1-mIgG1 only bound well to the acetylated form, consistent with differences in fine specificity. In engineering hybrid mIgG1/mIgG3 antibodies, we found that switching the 2H1-mIgG3 hinge for its mIgG1 counterpart changed the immunofluorescence pattern to annular, but a 2H1-mIgG1 antibody with a mIgG3 hinge still had an annular pattern. The hinge is thus necessary but not sufficient for these changes in binding to the antigen. This important role for the constant region in binding of antibodies to the antigen could affect the design of therapeutic antibodies and our understanding of their function in immunity. Key pointsO_LIKey point 1- 2H1 antibodies recapitulate differences between mIgG isotypes observed with 3E5. C_LIO_LIKey point 2 - The hinge region is necessary but not sufficient for these differences. C_LIO_LIKey point 3 - The antibody constant region can also play a role in mIgG binding to antigen. C_LI

immunology↗

bioRxiv2019

Exploring Cryptococcus neoformans capsule structure and assembly with a hydroxylamine-armed fluorescent probe

Chemical biology is an emerging field that allows the study and manipulation of biological systems using probes that inform on structure based on their reactivity. We report the synthesis of a hydroxylamine-armed fluorescent probe that reacts with reducing glycans and its application to study the architecture of the Cryptococcus neoformans capsule under a variety of conditions. The probe signal localized intracellularly and at the cell wall-membrane interface, implying the presence of reducing end glycans at this location where the capsule attachment to the cell body occurs. In contrast, there was no fluorescence signal in the body of the capsule. We observed vesicle-like structures containing the reducing-end probe, both intra- and extracellularly, consistent with the importance of vesicles in capsular assembly. Disrupting the capsule with DMSO, ultrasound, or mechanical shear-stress resulted in capsule alterations that affected the binding of the probe as reducing ends were exposed, and cell membrane integrity was compromised. In contrast to the polysaccharides in the assembled capsule, isolated exopolysaccharides contained reducing ends. The reactivity of the hydroxylamine-armed fluorescent probe suggests a model for capsule assembly where reducing ends localize to the cell wall surface, supporting previous work suggesting that this is an initiation point for capsular assembly. Chemical biology is a promising approach for studying the C. neoformans capsule and its associated polysaccharides.

microbiology↗