beta-1,3-Glucan in Developing Cotton Fibers: Structure, Localization, and Relationship of Synthesis to That of Secondary Wall Cellulose

Evidence is presented for the existence of a noncellulosic β-1,3-glucan in cotton fibers. The glucan can be isolated as distinct fractions of varying solubility. When fibers are homogenized rigorously in aqueous buffer, part of the total β-1,3-glucan is found as a soluble polymer in homogenates freed of cell walls. The proportion of total β-1,3-glucan which is found as the soluble polymer varies somewhat as a function of fiber age. The insoluble fraction of the β-1,3-glucan remains associated with the cell wall fraction. Of this cell wall β-1,3-glucan, a variable portion can be solubilized by treatment of walls with hot water, a further portion can be solubilized by alkaline extraction of the walls, and 17 to 29% of the glucan remains associated with cellulose even after alkaline extraction. A portion of this glucan can also be removed from the cell walls of intact cotton fibers by digestion with an endo-β-1,3-glucanase. The glucan fraction which can be isolated as a soluble polymer in homogenates freed of cell walls is not associated with membranous material, and we propose that it represents glucan which is also extracellular but not tightly associated with the cell wall. Enzyme digestion studies indicate that all of the cotton fiber glucan is β-linked, and methylation analyses and enzyme studies both show that the predominant linkage in the glucan is 1 → 3. The possibility of some minor branching at C-6 can also be deduced from the methylation analyses. The timing of deposition of the β-1,3-glucan during fiber development coincides closely with the onset of secondary wall cellulose synthesis. Kinetic studies performed with ovules and fibers cultured in vitro show that incorporation of radioactivity from [¹⁴C]glucose into β-1,3-glucan is linear with respect to time almost from the start of the labeling period; however, a lag is observed before incorporation into cellulose becomes linear with time, suggesting that these two different glucans are not polymerized directly from the same substrate pool. Pulse-chase experiments indicate that neither the β-1,3-glucan nor cellulose exhibits significant turnover after synthesis.     

Changes in beta-1,3-Glucan Synthase Activity in Developing Lima Bean Plants

A plasma membrane-enriched fraction was isolated from various tissues of developing lima bean seedlings, Phaseolus lunatus var Cangreen, to study β-1,3-glucan synthase activity changes. All tissues contained an active β-glucan synthase, including the cotyledons that will be senescent in mature lima bean plants. Young primary leaves exhibited a very active β-glucan synthase; but this activity dropped markedly, about fivefold, as the leaves gained weight and became photosynthetic. Some tissues, such as the hypocotyl and young stem, exhibited an increase in β-glucan synthase activity as the tissues were growing and a decrease as the growth rate slowed. Roots exhibited a high activity early in development that only decreased slightly, about 30%, as root growth increased. Surprisingly the senescent cotyledons contained an activity equivalent to some other tissues that was maintained over our measurement time of 21 days. Perhaps this callose synthesis activity is related to translocation processes as the cotyledons transfer their reserves to the growing seedling. We concluded that β-glucan synthase was not a good indicator of sink strength in these lima bean tissues. The plasma membrane fractions also were tested for other enzymes that might be present because an electron microscope study revealed a low contamination by other types of membranes. The membrane fractions had low but detectable activities of sucrose synthase, UDPglucose pyrophosphorylase, UDPase, alkaline invertase, and a general phosphatase; but these enzymes exhibited no consistent pattern(s) of activity change with plant development.     

beta-1, 3-Glucan Synthase from Lilium longiflorum Pollen

A particulate fraction from pollen tubes and ungerminated pollen of Lilium longiflorum incorporated ¹⁴C-glucose from UDP-glucose-¹⁴C into a lipid fraction and into β-1, 3-glucan. Partial hydrolysis of the glucan yielded laminaribiose as the only radioactive disaccharide. The preferred substrate was UDP-glucose, and enzyme activity was stimulated by glucose and by β-linked di- and trisaccharides. Enzyme from growing pollen tubes synthesized β-1, 3-glucan more rapidly and produced a higher proportion of alkali-insoluble glucan than did enzyme from ungerminated pollen. The onset of pollen tube growth may be dependent on altered activity of β-1, 3-glucan synthase.     

Pea Xyloglucan and Cellulose: VI. Xyloglucan-Cellulose Interactions in Vitro and in Vivo

Since xyloglucan is believed to bind to cellulose microfibrils in the primary cell walls of higher plants and, when isolated from the walls, can also bind to cellulose in vitro, the binding mechanism of xyloglucan to cellulose was further investigated using radioiodinated pea xyloglucan. A time course for the binding showed that the radioiodinated xyloglucan continued to be bound for at least 4 hours at 40°C. Binding was inhibited above pH 6. Binding capacity was shown to vary for celluloses of different origin and was directly related to the relative surface area of the microfibrils. The binding of xyloglucan to cellulose was very specific and was not affected by the presence of a 10-fold excess of (1→2)-β-glucan, (1→3)-β-glucan, (1→6)-β-glucan, (1→3, 1→4)-β-glucan, arabinogalactan, or pectin. When xyloglucan (0.1%) was added to a cellulose-forming culture of Acetobacter xylinum, cellulose ribbon structure was partially disrupted indicating an association of xyloglucan with cellulose at the time of synthesis. Such a result suggests that the small size of primary wall microfibrils in higher plants may well be due to the binding of xyloglucan to cellulose during synthesis which prevents fasciation of small fibrils into larger bundles. Fluorescent xyloglucan was used to stain pea cell wall ghosts prepared to contain only the native xyloglucan:cellulose network or only cellulose. Ghosts containing only cellulose showed strong fluorescence when prepared before or after elongation; as predicted, the presence of native xyloglucan in the ghosts repressed binding of added fluorescent xyloglucan. Such ghosts, prepared after elongation when the ratio of native xyloglucan:cellulose is substantially reduced, still showed only faint fluorescence, indicating that microfibrils continue to be coated with xyloglucan throughout the growth period.     

Architecture and Biosynthesis of the Saccharomyces cerevisiae Cell Wall

The wall gives a Saccharomyces cerevisiae cell its osmotic integrity; defines cell shape during budding growth, mating, sporulation, and pseudohypha formation; and presents adhesive glycoproteins to other yeast cells. The wall consists of β1,3- and β1,6-glucans, a small amount of chitin, and many different proteins that may bear N- and O-linked glycans and a glycolipid anchor. These components become cross-linked in various ways to form higher-order complexes. Wall composition and degree of cross-linking vary during growth and development and change in response to cell wall stress. This article reviews wall biogenesis in vegetative cells, covering the structure of wall components and how they are cross-linked; the biosynthesis of N- and O-linked glycans, glycosylphosphatidylinositol membrane anchors, β1,3- and β1,6-linked glucans, and chitin; the reactions that cross-link wall components; and the possible functions of enzymatic and nonenzymatic cell wall proteins.     

Protection by Anti-β-Glucan Antibodies Is Associated with Restricted β-1,3 Glucan Binding Specificity and Inhibition of Fungal Growth and Adherence

Anti-β-glucan antibodies elicited by a laminarin-conjugate vaccine confer cross-protection to mice challenged with major fungal pathogens such as Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. To gain insights into protective β-glucan epitope(s) and protection mechanisms, we studied two anti-β-glucan monoclonal antibodies (mAb) with identical complementarity-determining regions but different isotypes (mAb 2G8, IgG2b and mAb 1E12, IgM). C. albicans, the most relevant fungal pathogen for humans, was used as a model.Both mAbs bound to fungal cell surface and to the β1,3-β1,6 glucan of the fungal cell wall skeleton, as shown by immunofluorescence, electron-microscopy and ELISA. They were also equally unable to opsonize fungal cells in a J774 macrophage phagocytosis and killing assay. However, only the IgG2b conferred substantial protection against mucosal and systemic candidiasis in passive vaccination experiments in rodents. Competition ELISA and microarray analyses using sequence-defined glucan oligosaccharides showed that the protective IgG2b selectively bound to β1,3-linked (laminarin-like) glucose sequences whereas the non-protective IgM bound to β1,6- and β1,4-linked glucose sequences in addition to β1,3-linked ones. Only the protective IgG2b recognized heterogeneous, polydisperse high molecular weight cell wall and secretory components of the fungus, two of which were identified as the GPI-anchored cell wall proteins Als3 and Hyr1. In addition, only the IgG2b inhibited in vitro two critical virulence attributes of the fungus, hyphal growth and adherence to human epithelial cells.Our study demonstrates that the isotype of anti-β-glucan antibodies may affect details of the β-glucan epitopes recognized, and this may be associated with a differing ability to inhibit virulence attributes of the fungus and confer protection in vivo. Our data also suggest that the anti-virulence properties of the IgG2b mAb may be linked to its capacity to recognize β-glucan epitope(s) on some cell wall components that exert critical functions in fungal cell wall structure and adherence to host cells.     

The expansin superfamily

The expansin superfamily of plant proteins is made up of four families, designated α-expansin, β-expansin, expansin-like A and expansin-like B. α-Expansin and β-expansin proteins are known to have cell-wall loosening activity and to be involved in cell expansion and other developmental events during which cell-wall modification occurs. Proteins in these two families bind tightly to the cell wall and their activity is typically assayed by their stimulation of cell-wall extension and stress relaxation; no bona fide enzymatic activity has been detected for these proteins. α-Expansin proteins and some, but not all, β-expansin proteins are implicated as catalysts of 'acid growth', the enlargement of plant cells stimulated by low extracellular pH. A divergent group of β-expansin genes are expressed at high levels in the pollen of grasses but not of other plant groups. They probably function to loosen maternal cell walls during growth of the pollen tube towards the ovary. All expansins consist of two domains; domain 1 is homologous to the catalytic domain of proteins in the glycoside hydrolase family 45 (GH45); expansin domain 2 is homologous to group-2 grass pollen allergens, which are of unknown biological function. Experimental evidence suggests that expansins loosen cell walls via a nonenzymatic mechanism that induces slippage of cellulose microfibrils in the plant cell wall.     

Loss of the Plasma Membrane-Bound Protein Gas1p in Saccharomyces cerevisiae Results in the Release of β1,3-Glucan into the Medium and Induces a Compensation Mechanism To Ensure Cell Wall Integrity

Deletion of GAS1/GGP1/CWH52 results in a lower β-glucan content of the cell wall and swollen, more spherical cells (L. Popolo, M. Vai, E. Gatti, S. Porello, P. Bonfante, R. Balestrini, and L. Alberghina, J. Bacteriol. 175:1879–1885, 1993; A. F. J. Ram, S. S. C. Brekelmans, L. J. W. M. Oehlen, and F. M. Klis, FEBS Lett. 358:165–170, 1995). We show here that gas1Δ cells release β1,3-glucan into the medium. Western analysis of the medium proteins with β1,3-glucan- and β1,6-glucan-specific antibodies showed further that at least some of the released β1,3-glucan was linked to protein as part of a β1,3-glucan–β1,6-glucan–protein complex. These data indicate that Gas1p might play a role in the retention of β1,3-glucan and/or β-glucosylated proteins. Interestingly, the defective incorporation of β1,3-glucan in the cell wall was accompanied by an increase in chitin and mannan content in the cell wall, an enhanced expression of cell wall protein 1 (Cwp1p), and an increase in β1,3-glucan synthase activity, probably caused by the induced expression of Fks2p. It is proposed that the cell wall weakening caused by the loss of Gas1p induces a set of compensatory reactions to ensure cell integrity.     

A Neutral Thermostable β-1,4-Glucanase from Humicola insolens Y1 with Potential for Applications in Various Industries

We cloned a new glycoside hydrolase family 6 gene, Hicel6C, from the thermophilic fungus Humicola insolens Y1 and expressed it in Pichia pastoris. Using barley β-glucan as a substrate, recombinant HiCel6C protein exhibited neutral pH (6.5) and high temperature (70°C) optima. Distinct from most reported acidic fungal endo-β-1,4-glucanases, HiCel6C was alkali-tolerant, retaining greater than 98.0, 61.2, and 27.6% of peak activity at pH 8.0, 9.0, and 10.0, respectively, and exhibited good stability over a wide pH range (pH 5.0−11.0) and at temperatures up to 60°C. The K _m and V _max values of HiCel6C for barley β-glucan were 1.29 mg/mL and 752 μmol/min·mg, respectively. HiCel6C was strictly specific for the β-1,4-glucoside linkage exhibiting activity toward barley β-glucan, lichenan, and carboxy methylcellulose sodium salt (CMC-Na), but not toward laminarin (1,3-β-glucan). HiCel6C cleaved the internal glycosidic linkages of cellooligosaccharides randomly and thus represents an endo-cleaving enzyme. The predominant product of polysaccharide hydrolysis by HiCel6C was cellobiose, suggesting that it functions by an endo-processive mechanism. The favorable properties of HiCel6C make it a good candidate for basic research and for applications in the textile and brewing industries.     

The Role of Glucosidase I (Cwh41p) in the Biosynthesis of Cell Wall β-1,6-Glucan Is Indirect

CWH41, a gene involved in the assembly of cell wall β-1,6-glucan, has recently been shown to be the structural gene for Saccharomyces cerevisiae glucosidase I that is responsible for initiating the trimming of terminal α-1,2-glucose residue in the N-glycan processing pathway. To distinguish between a direct or indirect role of Cwh41p in the biosynthesis of β-1,6-glucan, we constructed a double mutant, alg5Δ (lacking dolichol-P-glucose synthase) cwh41Δ, and found that it has the same phenotype as the alg5Δ single mutant. It contains wild-type levels of cell wall β-1,6-glucan, shows moderate underglycosylation of N-linked glycoproteins, and grows at concentrations of Calcofluor White (which interferes with cell wall assembly) that are lethal to cwh41Δ single mutant. The strong genetic interactions of CWH41 with KRE6 and KRE1, two other genes involved in the β-1,6-glucan biosynthetic pathway, disappear in the absence of dolichol-P-glucose synthase (alg5Δ). The triple mutant alg5Δcwh41Δkre6Δ is viable, whereas the double mutant cwh41Δkre6Δ in the same genetic background is not. The severe slow growth phenotype and 75% reduction in cell wall β-1,6-glucan, characteristic of the cwh41Δkre1Δ double mutant, are not observed in the triple mutant alg5Δcwh41Δkre1Δ. Kre6p, a putative Golgi glucan synthase, is unstable in cwh41Δ strains, and its overexpression renders these cells Calcofluor White resistant. These results demonstrate that the role of glucosidase I (Cwh41p) in the biosynthesis of cell wall β-1,6-glucan is indirect and that dolichol-P-glucose is not an intermediate in this pathway.     

Bgs3p,a putative 1,3-beta-glucan synthase subunit,is required for cell wall assembly in Schizosaccharomyces pombe

β-Glucans are the main components of the fungal cell wall. Fission yeast possesses a family of β-glucan synthase-related genes. We describe here the cloning and characterization of bgs3⁺, a new member of this family. bgs3⁺ was cloned as a suppressor of a mutant hypersensitive to Echinocandin and Calcofluor White, drugs that interfere with cell wall biosynthesis. Disruption of the gene is lethal, and a decrease in Bgs3p levels leads to rounded cells with thicker walls, slightly reduces the amount of the β-glucan, and raises the amount of α-glucan polymer. These cells finally died. bgs3⁺ is expressed in vegetative cells grown in different conditions and during mating and germination and is not enhanced by stress situations. Consistent with the observed expression pattern, Bgs3-green fluorescence protein (GFP-Bgs3p) was found at the growing tips during interphase and at the septum prior to cytokinesis, always localized to growth areas. We also found GFP-Bgs3p in mating projections, during the early stages of zygote formation, and at the growing pole during ascospore germination. We conclude that Bgs3p localization is restricted to growth areas and that Bgs3p is a glucan synthase homologue required for cell wall biosynthesis and cell elongation in the fission yeast life cycle.     

A Highlights from MBoC Selection: Distinct roles of cell wall biogenesis in yeast morphogenesis as revealed by multivariate analysis of high-dimensional morphometric data

The cell wall of budding yeast is a rigid structure composed of multiple components. To thoroughly understand its involvement in morphogenesis, we used the image analysis software CalMorph to quantitatively analyze cell morphology after treatment with drugs that inhibit different processes during cell wall synthesis. Cells treated with cell wall–affecting drugs exhibited broader necks and increased morphological variation. Tunicamycin, which inhibits the initial step of N-glycosylation of cell wall mannoproteins, induced morphologies similar to those of strains defective in α-mannosylation. The chitin synthase inhibitor nikkomycin Z induced morphological changes similar to those of mutants defective in chitin transglycosylase, possibly due to the critical role of chitin in anchoring the β-glucan network. To define the mode of action of echinocandin B, a 1,3-β-glucan synthase inhibitor, we compared the morphology it induced with mutants of Fks1 that contains the catalytic domain for 1,3-β-glucan synthesis. Echinocandin B exerted morphological effects similar to those observed in some fks1 mutants, with defects in cell polarity and reduced glucan synthesis activity, suggesting that echinocandin B affects not only 1,3-β-glucan synthesis, but also another functional domain. Thus our multivariate analyses reveal discrete functions of cell wall components and increase our understanding of the pharmacology of antifungal drugs.     

Infection Structure–Specific Expression of β-1,3-Glucan Synthase Is Essential for Pathogenicity of Colletotrichum graminicola and Evasion of β-Glucan–Triggered Immunity in Maize

β-1,3-Glucan and chitin are the most prominent polysaccharides of the fungal cell wall. Covalently linked, these polymers form a scaffold that determines the form and properties of vegetative and pathogenic hyphae. While the role of chitin in plant infection is well understood, the role of β-1,3-glucan is unknown. We functionally characterized the β-1,3-glucan synthase gene GLS1 of the maize (Zea mays) pathogen Colletotrichum graminicola, employing RNA interference (RNAi), GLS1 overexpression, live-cell imaging, and aniline blue fluorochrome staining. This hemibiotroph sequentially differentiates a melanized appressorium on the cuticle and biotrophic and necrotrophic hyphae in its host. Massive β-1,3-glucan contents were detected in cell walls of appressoria and necrotrophic hyphae. Unexpectedly, GLS1 expression and β-1,3-glucan contents were drastically reduced during biotrophic development. In appressoria of RNAi strains, downregulation of β-1,3-glucan synthesis increased cell wall elasticity, and the appressoria exploded. While the shape of biotrophic hyphae was unaffected in RNAi strains, necrotrophic hyphae showed severe distortions. Constitutive expression of GLS1 led to exposure of β-1,3-glucan on biotrophic hyphae, massive induction of broad-spectrum defense responses, and significantly reduced disease symptom severity. Thus, while β-1,3-glucan synthesis is required for cell wall rigidity in appressoria and fast-growing necrotrophic hyphae, its rigorous downregulation during biotrophic development represents a strategy for evading β-glucan–triggered immunity.     

The Characterization of the Endoglucanase Cel12A from Gloeophyllum trabeum Reveals an Enzyme Highly Active on β-Glucan

The basidiomycete fungus Gloeophyllum trabeum causes a typical brown rot and is known to use reactive oxygen species in the degradation of cellulose. The extracellular Cel12A is one of the few endo-1,4-β-glucanase produced by G. trabeum. Here we cloned cel12A and heterologously expressed it in Aspergillus niger. The identity of the resulting recombinant protein was confirmed by mass spectrometry. We used the purified GtCel12A to determine its substrate specificity and basic biochemical properties. The G. trabeum Cel12A showed highest activity on β-glucan, followed by lichenan, carboxymethylcellulose, phosphoric acid swollen cellulose, microcrystalline cellulose, and filter paper. The optimal pH and temperature for enzymatic activity were, respectively, 4.5 and 50°C on β-glucan. Under these conditions specific activity was 239.2±9.1 U mg⁻¹ and the half-life of the enzyme was 84.6±3.5 hours. Thermofluor studies revealed that the enzyme was most thermal stable at pH 3. Using β-glucan as a substrate, the K_m was 3.2±0.5 mg mL⁻¹ and the V_max was 0.41±0.02 µmol min⁻¹. Analysis of the effects of GtCel12A on oat spelt and filter paper by scanning electron microscopy revealed the morphological changes taking place during the process.     

Chemical structure of the cell walls of dwarf maize and changes mediated by gibberellin

Dwarf maize (Zea mays L.), a mutant deficient in gibberellin synthesis, provides an excellent model to study the influence of gibberellin on biochemical processes related to plant development. Alterations in the chemical structure of the cell wall mediated by gibberellin were examined in seedlings of this mutant. The composition of the walls of roots, mesocotyl, coleoptile, and primary leaves of dwarf maize was similar to that of normal maize and other cereal grasses. Glucuronoarabinoxylans constituted the principal hemicelluloses, but walls also contained substantial amounts of xyloglucan and mixed-linkage β-d-glucan. Root growth in dwarf maize was essentially normal, but growth of mesocotyl and primary leaves was severely retarded. Injection of the gibberellin into the cavity of the coleoptile resulted in a marked increase in elongation of the primary leaves. This elongation was accompanied by increases in total wall mass, but the proportion of β-d-glucan decreased from 20% to 15% of the hemicellulosic polysaccharide. During leaf expansion, the proportion decreased further to only 10%. Through 4 days incubation, the proportion of β-d-glucan in leaves of control seedlings without gibberellin was nearly constant. Extraction of exo- and endo-β-d-glucan hydrolases from purified cell walls and assay against a purified oat bran β-d-glucan demonstrated that gibberellin increased the activity of the endo-β-d-glucan hydrolase. These and other data support the hypothesis that β-d-glucan metabolism is central to control of cell expansion in cereal grasses.     

Chemical Organization of the Cell Wall Polysaccharide Core of Malassezia restricta

Malassezia species are ubiquitous residents of human skin and are associated with several diseases such as seborrheic dermatitis, tinea versicolor, folliculitis, atopic dermatitis, and scalp conditions such as dandruff. Host-Malassezia interactions and mechanisms to evade local immune responses remain largely unknown. Malassezia restricta is one of the most predominant yeasts of the healthy human skin, its cell wall has been investigated in this paper. Polysaccharides in the M. restricta cell wall are almost exclusively alkali-insoluble, showing that they play an essential role in the organization and rigidity of the M. restricta cell wall. Fractionation of cell wall polymers and carbohydrate analyses showed that the polysaccharide core of the cell wall of M. restricta contained an average of 5% chitin, 20% chitosan, 5% β-(1,3)-glucan, and 70% β-(1,6)-glucan. In contrast to other yeasts, chitin and chitosan are relatively abundant, and β-(1,3)-glucans constitute a minor cell wall component. The most abundant polymer is β-(1,6)-glucans, which are large molecules composed of a linear β-(1,6)-glucan chains with β-(1,3)-glucosyl side chain with an average of 1 branch point every 3.8 glucose unit. Both β-glucans are cross-linked, forming a huge alkali-insoluble complex with chitin and chitosan polymers. Data presented here show that M. restricta has a polysaccharide organization very different of all fungal species analyzed to date.     

Aspergillus nidulans Cell Wall Composition and Function Change in Response to Hosting Several Aspergillus fumigatus UDP-Galactopyranose Mutase Activity Mutants

Deletion or repression of Aspergillus nidulans ugmA (AnugmA), involved in galactofuranose biosynthesis, impairs growth and increases sensitivity to Caspofungin, a β-1,3-glucan synthesis antagonist. The A. fumigatus UgmA (AfUgmA) crystal structure has been determined. From that study, AfUgmA mutants with altered enzyme activity were transformed into AnugmA▵ to assess their effect on growth and wall composition in A. nidulans. The complemented (AnugmA::wild type AfugmA) strain had wild type phenotype, indicating these genes had functional homology. Consistent with in vitro studies, AfUgmA residues R182 and R327 were important for its function in vivo, with even conservative amino (RK) substitutions producing AnugmA? phenotype strains. Similarly, the conserved AfUgmA loop III histidine (H63) was important for Galf generation: the H63N strain had a partially rescued phenotype compared to AnugmA▵. Collectively, A. nidulans strains that hosted mutated AfUgmA constructs with low enzyme activity showed increased hyphal surface adhesion as assessed by binding fluorescent latex beads. Consistent with previous qPCR results, immunofluorescence and ELISA indicated that AnugmA▵ and AfugmA-mutated A. nidulans strains had increased α-glucan and decreased β-glucan in their cell walls compared to wild type and AfugmA-complemented strains. Like the AnugmA▵ strain, A. nidulans strains containing mutated AfugmA showed increased sensitivity to antifungal drugs, particularly Caspofungin. Reduced β-glucan content was correlated with increased Caspofungin sensitivity. Aspergillus nidulans wall Galf, α-glucan, and β-glucan content was correlated in A. nidulans hyphal walls, suggesting dynamic coordination between cell wall synthesis and cell wall integrity.     

Dynamic,Morphotype-Specific Candida albicans β-Glucan Exposure during Infection and Drug Treatment

Candida albicans, a clinically important dimorphic fungal pathogen that can evade immune attack by masking its cell wall β-glucan from immune recognition, mutes protective host responses mediated by the Dectin-1 β-glucan receptor on innate immune cells. Although the ability of C. albicans to switch between a yeast- or hyphal-form is a key virulence determinant, the role of each morphotype in β-glucan masking during infection and treatment has not been addressed. Here, we show that during infection of mice, the C. albicans β-glucan is masked initially but becomes exposed later in several organs. At all measured stages of infection, there is no difference in β-glucan exposure between yeast-form and hyphal cells. We have previously shown that sub-inhibitory doses of the anti-fungal drug caspofungin can expose β-glucan in vitro, suggesting that the drug may enhance immune activity during therapy. This report shows that caspofungin also mediates β-glucan unmasking in vivo. Surprisingly, caspofungin preferentially unmasks filamentous cells, as opposed to yeast form cells, both in vivo and in vitro. The fungicidal activity of caspofungin in vitro is also filament-biased, as corroborated using yeast-locked and hyphal-locked mutants. The uncloaking of filaments is not a general effect of anti-fungal drugs, as another anti-fungal agent does not have this effect. These results highlight the advantage of studying host–pathogen interaction in vivo and suggest new avenues for drug development.