Purification and properties of an extracellular lipase from the fungus Botrytis cinerea

Industrial applications of fungal lipases: a review

Fungal lipases (triacylglycerol acyl hydrolases EC 3.1.1.3) are significant industrial enzymes and have several applications in a number of industries and fields. Fungal lipases are found in several species of fungi and yeast. These enzymes are carboxylic acid esterases, categorized under the serine hydrolase family, and do not require any cofactor during the catalyzing of the reactions. It was also noticed that processes including the extraction and purification of lipases from fungi are comparatively easier and cheaper than other sources of lipases. In addition, fungal lipases have been classified into three chief classes, namely, GX, GGGX, and Y. Fungal lipases have applications not only in the hydrolysis of fats and oils (triglycerides) but are also involved in synthetic reactions such as esterification, acidolysis, alcoholysis, interesterification, and aminolysis. The production and activity of fungal lipases are highly affected by the carbon source, nitrogen source, temperature, pH, metal ions, surfactants, and moisture content. Therefore, fungal lipases have several industrial and biotechnological applications in many fields such as biodiesel production, ester synthesis, production of biodegradable biopolymers, formulations of cosmetics and personal care products, detergent manufacturing, degreasing of leather, pulp and paper production, textile industry, biosensor development, and drug formulations and as a diagnostic tool in the medical sector, biodegradation of esters, and bioremediation of wastewater. The immobilization of fungal lipases onto different carriers also helps in improving the catalytic activities and efficiencies of lipases by increasing thermal and ionic stability (in organic solvents, high pH, and temperature), being easy to recycle, and inducing the volume-specific loading of the enzyme onto the support, and thus, these features have proved to be appropriate for use as biocatalysts in different sectors.

Generation of Antifungal Stilbenes Using the Enzymatic Secretome of Botrytis cinerea

The protein secretome of Botrytis cinerea was used to perform the biotransformation of resveratrol, pterostilbene, and a mixture of both. Metabolite profiling by UHPLC-HRMS revealed the presence of compounds with unusual molecular formula, suggesting the existence of new products. To isolate these products, the reactions were scaled-up, and 21 analogues were isolated and fully characterized by NMR and HRESIMS analyses. The reaction with pterostilbene afforded five new compounds, while the reaction with a mixture of pterostilbene and resveratrol afforded seven unusual stilbene dimers. The antifungal properties of these compounds were evaluated using in vitro bioassays against Plasmopara viticola. The cytological effects of the isolated antifungal compounds on the ultrastructure of P. viticola were also evaluated.

A secreted lipolytic enzyme from Xanthomonas campestris pv. vesicatoria is expressed in planta and contributes to its virulence

A recombinase-based in vivo expression technology (RIVET) approach with Xanthomonas campestris pv. vesicatoria (Xcv) revealed that lipA, annotated as putative secreted lipase, is expressed during the interaction between this pathogen and tomato. Here, the tnpR and uidA reporter genes were used to show that lipA is strongly induced in XVM2 minimal medium and during the early stages of tomato infection by Xcv. A mutant strain impaired in lipA was generated by insertional mutagenesis. This mutant grew in a similar manner to the wild-type in rich medium, but its growth was significantly compromised in a medium containing olive oil as a single carbon source. The lipolytic activity of the extracellular fraction of the lipA mutant was reduced significantly relative to that of the wild-type strain, thus confirming that lipA indeed encodes a functional secreted enzyme with lipolytic activity. A plasmid carrying a wild-type copy of lipA complemented the lipA mutant for extracellular lipolytic activity. Dip inoculation experiments with tomato lines Hawaii 7998 (H7998) and Micro Tom showed that the lipA mutant grew to a lesser extent than the wild-type in tomato leaves. Following leaf syringe infiltrations, the mutant strain induced disease symptoms that were less severe than those induced by the wild-type strain, supporting a significant role of lipA in the pathogenicity of Xcv.

Overview of fungal lipase: a review

Lipases (triacylglycerolacyl hydrolases, EC3.1.1.3) are class of enzymes which catalyze the hydrolysis of long-chain triglycerides. In this review paper, an overview regarding the fungal lipase production, purification, and application is discussed. The review describes various industrial applications of lipase in pulp and paper, food, detergent, and textile industries. Some important lipase-producing fungal genera include Aspergillus, Penicillium, Rhizopus, Candida, etc. Current fermentation process techniques such as batch, fed-batch, and continuous mode of lipase production in submerged and solid-state fermentations are discussed in details. The purification of lipase by hydrophobic interaction chromatography is also discussed. The development of mathematical models applied to lipase production is discussed with special emphasis on lipase engineering.

Aspergillus flavus

Aspergillus flavus is saprophytic soil fungus that infects and contaminates preharvest and postharvest seed crops with the carcinogenic secondary metabolite aflatoxin. The fungus is also an opportunistic animal and human pathogen causing aspergillosis diseases with incidence increasing in the immunocompromised population. Whole genome sequences of A. flavus have been released and reveal 55 secondary metabolite clusters that are regulated by different environmental regimes and the global secondary metabolite regulators LaeA and VeA. Characteristics of A. flavus associated with pathogenicity and niche specialization include secondary metabolite production, enzyme elaboration, and a sophisticated oxylipin host crosstalk associated with a quorum-like development program. One of the more promising strategies in field control involves the use of atoxic strains of A. flavus in competitive exclusion studies. In this review, we discuss A. flavus as an agricultural and medical threat and summarize recent research advances in genomics, elucidation of parameters of pathogenicity, and control measures.

Methods for detection and characterization of lipases: A comprehensive review

Microbial lipases are very prominent biocatalysts because of their ability to catalyze a wide variety of reactions in aqueous and non-aqueous media. The chemo-, regio- and enantio-specific behaviour of these enzymes has caused tremendous interest among scientists and industrialists. Lipases from a large number of bacterial, fungal and a few plant and animal sources have been purified to homogeneity. This article presents a critical review of different strategies which have been employed for the detection, purification and characterization of microbial lipases.

Characterization and expression analysis of a gene encoding a secreted lipase-like protein expressed in the salivary glands of the larval Hessian fly, Mayetiola destructor (Say)

In a salivary gland transcriptomics study we identified a cDNA with a full-length open reading frame for a gene (MdesL1) encoding a lipase-like protein expressed in the salivary glands of the larval Hessian fly, Mayetiola destructor (Say). Fluorescent in situ hybridization on salivary polytenes positioned MdesL1 on the long arm of Autosome 1. BLASTp and conserved domain searches revealed the deduced amino acid sequence contained a lipase superfamily domain with similarity to lipases and phospholipases from other insects. A secretion signal peptide was identified at the amino terminus of the deduced amino acid sequence. Analysis of the transcript of MdesL1 in larval Hessian fly tissues by quantitative real-time PCR (qPCR) revealed the greatest abundance was in salivary glands. Analysis of transcript levels during development showed the greatest level was detected in feeding 1st-instar and early 2nd-instar larvae. Transcript levels increased dramatically over time in larvae feeding on susceptible wheat but were detected at low levels in larvae feeding on resistant wheat. These data suggest the protein encoded by MdesL1 is likely secreted into host-plant cells during larval feeding and could be involved in extra-oral digestion and changes in host-cell permeability or in generating a second messenger in a host-cell-signaling cascade.

Crystallization and preliminary crystallographic analysis of Gibberella zeae extracellular lipase

Fusarium head blight, one of the most destructive crop diseases, is mainly caused by Fusarium graminearum (known in its sexual stage as Gibberella zeae). F. graminearum secretes various extracellular enzymes that have been hypothesized to be involved in host infection. One of the extracellular enzymes secreted by this organism is the G. zeae extracellular lipase (GZEL), which is encoded by the FGL1 gene. In order to solve the crystal structure of GZEL and to gain a better understanding of the biological functions of the protein and of possible inhibitory mechanisms of lipase inhibitors, recombinant GZEL was crystallized at 291 K using PEG 3350 as a precipitant. A data set was collected to 2.8 A resolution from a single flash-cooled crystal (100 K). The crystal belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 78.4, b = 91.0, c = 195.8 A, alpha = beta = gamma = 90 degrees . The presence of four molecules was assumed per asymmetric unit, which gave a Matthews coefficient of 2.6 A(3) Da(-1).

Requirement of LaeA for secondary metabolism and sclerotial production in Aspergillus flavus

The nuclear regulator LaeA has been shown to govern production of multiple secondary metabolites in Aspergillus nidulans and Aspergillus fumigatus. Herein we examine the role of this protein in Aspergillus flavus. Similarly as in other Aspergilli, LaeA had a major effect on A. flavus secondary metabolism where DeltalaeA and over-expression laeA (OE::laeA) strains yielded opposite phenotypes resulting in decreased (increased) secondary metabolite production. The two mutant strains also exhibited striking morphological phenotypes in the loss (increase) of sclerotial production in comparison to wildtype. Growth on seed was marked by decreased (increased) conidial and aflatoxin production of the respective mutants; this was accompanied by decreased lipase activity in DeltalaeA, an enzymatic process correlated with seed maceration. Transcriptional examination of the mutants showed LaeA negatively regulates expression of its recently identified nuclear partner VeA, another global regulator of A. flavus secondary metabolites and sclerotia.

Purification and biochemical characterization of a broad substrate specificity thermostable alkaline protease from Aspergillus nidulans

Aspergillus nidulans PW1 produces an extracellular carboxylesterase activity that acts on several lipid esters when cultured in liquid media containing olive oil as a carbon source. The enzyme was purified by gel filtration and ion exchange chromatography. It has an apparent MW and pI of 37 kDa and 4.5, respectively. The enzyme efficiently hydrolyzed all assayed glycerides, but showed preference toward short- and medium-length chain fatty acid esters. Maximum activity was obtained at pH 8.5 at 40 degrees C. The enzyme retained activity after incubation at pHs ranging from 8 to 11 for 12 h at 37 degrees C and 6 to 8 for 24 h at 37 degrees C. It retained 80% of its activity after incubation at 30 to 70 degrees C for 30 min and lost 50% of its activity after incubation for 15 min at 80 degrees C. Noticeable activation of the enzyme is observed when Fe(2+) ion is present at a concentration of 1 mM. Inhibition of the enzyme is observed in the presence of Cu(2+), Fe(3+), Hg(2+), and Zn(2+) ions. Even though the enzyme showed strong carboxylesterase activity, the deduced N-terminal amino acid sequence of the purified protein corresponded to the protease encoded by prtA gene.

The multifunctional beta-oxidation enzyme is required for full symptom development by the biotrophic maize pathogen Ustilago maydis

The transition from yeast-like to filamentous growth in the biotrophic fungal phytopathogen Ustilago maydis is a crucial event for pathogenesis. Previously, we showed that fatty acids induce filamentation in U. maydis and that the resulting hyphal cells resemble the infectious filaments observed in planta. To explore the potential metabolic role of lipids in the morphological transition and in pathogenic development in host tissue, we deleted the mfe2 gene encoding the multifunctional enzyme that catalyzes the second and third reactions in beta-oxidation of fatty acids in peroxisomes. The growth of the strains defective in mfe2 was attenuated on long-chain fatty acids and abolished on very-long-chain fatty acids. The mfe2 gene was not generally required for the production of filaments during mating in vitro, but loss of the gene blocked extensive proliferation of fungal filaments in planta. Consistent with this observation, mfe2 mutants exhibited significantly reduced virulence in that only 27% of infected seedlings produced tumors compared to 88% tumor production upon infection by wild-type strains. Similarly, a defect in virulence was observed in developing ears upon infection of mature maize plants. Specifically, the absence of the mfe2 gene delayed the development of teliospores within mature tumor tissue. Overall, these results indicate that the ability to utilize host lipids contributes to the pathogenic development of U. maydis.

Oxylipins act as determinants of natural product biosynthesis and seed colonization in Aspergillus nidulans

Secreted, hormone-like lipogenic molecules, called oxylipins, mediate the balance of asexual to sexual spore ratio in Aspergillus nidulans. Oxylipin production in this fungus is dependent on developmental regulation of three conserved fatty acid oxygenases, PpoA, PpoB and PpoC. Here, we show that in addition to altering spore ratios, loss of ppo genes affect natural product biosynthesis and seed colonization. DeltappoA;DeltappoC and DeltappoA;DeltappoB;DeltappoC mutants were unable to produce the mycotoxin sterigmatocystin (ST) in vitro or in planta but in contrast overproduced the antibiotic penicillin (PN). These findings were correlated with decreased expression of genes involved in ST biosynthesis and increased expression of a PN biosynthetic gene, thus suggesting that oxylipin species regulate secondary metabolites at the transcriptional level. Additionally, the DeltappoA;DeltappoC and the DeltappoA;DeltappoB;DeltappoC mutants were defective in colonization of peanut seeds as reflected by a decrease in conidiation and production of the seed degradative enzyme lipase. These results indicate that oxylipin production is important for host colonization and mycotoxin production and may provide a promising target for future control strategies.

A secreted lipase encoded by LIP1 is necessary for efficient use of saturated triglyceride lipids in Fusarium graminearum

A triglyceride lipase gene LIP1 was identified in the genome of Fusarium graminearum strain PH-1. The predicted protein encoded by LIP1 contains 591 amino acid residues with a putative N-terminal signal peptide and shows 57 and 40-44 % identity to a Botrytis cinerea lipase and five Candida rugosa lipases, respectively. Yeast cells overexpressing LIP1 showed lipolytic activity against a broad range of triglyceride substrates. Northern blot analyses revealed that expression of LIP1 was activated in planta during the fungal infection process. LIP1 expression was strongly induced in minimal medium supplemented with wheatgerm oil, but only weakly induced by olive oil and triolein. In contrast, supplementation with other carbon sources, including glucose, sucrose, apple pectin and wheat cell-wall material, did not induce LIP1 expression. Saturated fatty acids were the strongest inducers for LIP1 expression and this induction was suppressed proportionally by the presence of the unsaturated fatty acid. To determine the potential function of LIP1, gene replacement was conducted on strain PH-1. When compared with wild-type PH-1, DeltaLIP1 mutants showed greatly reduced lipolytic activities at the early stage of incubation on minimal medium supplemented with either saturated or unsaturated lipid as the substrate, indicating that LIP1 encodes a secreted lipase for exogenous lipid hydrolysis. Moreover, the DeltaLIP1 mutants exhibited growth deficiency on both liquid and solid minimal media supplemented with the saturated triglyceride tristearin as the sole carbon source, suggesting that LIP1 is required for utilization of this substance. Despite these differences, no variation in disease symptoms between the DeltaLIP1 mutants and the wild-type strain was observed on susceptible cereal hosts.

A secreted lipase of Fusarium graminearum is a virulence factor required for infection of cereals

Fusarium graminearum is the causal agent of the Fusarium head blight (FHB) and a destructive pathogen of cereals accounting for high grain yield losses especially on wheat and maize. Like other fungal pathogens, F. graminearum secretes various extracellular enzymes, which are hypothesized to be involved in host infection. Extracellular lipolytic activity of F. graminearum was strongly induced in culture by wheat germ oil; this allowed us to isolate, clone, and characterize a gene (FGL1) encoding a secreted lipase. Expression analysis indicated that FGL1 is induced by lipid-containing substrates and repressed by glucose. In planta, FGL1 transcription was detected 1 day post-infection of wheat spikes. The function of the FGL1 gene product was verified by specifically demonstrating lipase activity after expression in a heterologous host. Ebelactone B, a known lipase inhibitor, repressed the lipolytic activity of the enzyme. Disease severity was strongly reduced when wild-type conidia were supplemented with ebelactone B. Transformation-mediated disruption of FGL1 led to reduced extracellular lipolytic activity in culture and to reduced virulence to both wheat and maize.

Molecular and functional characterization of a secreted lipase from Botrytis cinerea

SUMMARY A previous study has indicated that a cutinolytic lipase from Botrytis cinerea was required for penetration of an intact plant host cuticle and infection (Comménil et al., 1998, Physiol. Mol. Plant Pathol. 52, 1-14). In order to clarify the role of this lipase, the corresponding gene (lip1) was cloned. In vitro, the lip1-encoded lipase was inducibly expressed and subject to catabolite repression. On the leaf surface, the cuticle served as an inducer. lip1 knock-out mutants lacked lipase activity; however, no reduction of virulence was observed. To further eliminate cutinolytic activity, the gene encoding cutinase A was also disrupted. In lip1cutA double mutants, extracellular esterases were largely eliminated in vitro and greatly reduced on the leaf surface; yet these mutants also retained full pathogenicity in various host systems. Our data indicate that cutinase and esterase activities are secreted by germinating B. cinerea spores on the surface of host leaves, but they do not seem to be required for host cuticle penetration.

Purification and characterization of an extracellular lipase from Geotrichum marinum

An extracellular lipase (EC 3.1.1.3) from Geotrichum marinum was purified 76-fold with 46% recovery using Octyl Sepharose 4 Fast Flow and Bio-Gel A 1.5 m chromatography. The purified enzyme showed a prominent band on SDS-PAGE and a single band on native PAGE based on the activity staining. The molecular mass of the lipase was estimated to be 62 kDa using SDS-PAGE and Bio-Gel A chromatography, indicating that the lipase likely functions as a monomer. The pl of the lipase was determined to be 4.54. The apparent V(max) and Km were 1000 micromol/min/mg protein and 11.5 mM, respectively, using olive oil emulsified with taurocholic acid as substrate. The lipase demonstrated a pH optimum at pH 8.0 and a temperature optimum at 40 degrees C. At 6 mM, Na+, K+, Ca2+, and Mg2+ stimulated activity, but Na+ and K+ at 500 mM and Fe2+ and Mn2+ at 6 mM reduced lipase activity. The anionic surfactant, taurocholic acid, and the zwitterionic surfactant, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, enhanced the activity at 0.1 mM. Other anionic surfactants such as SDS and sodium dioctyl sulfosuccinate, the cationic surfactants methylbenzethonium bromide and cetyltriethylammonium bromide, and the nonionic surfactants Tween-20 and Triton X-100 inhibited the lipase activity to different extents. The lipase was found to have a preference for TG containing cis double bonds in their FA side chains, and the reaction rate increased with an increasing number of double bonds in the side chain. The lipase had a preference for ester bonds at the sn-1 and sn-3 positions over the ester bond at the sn-2 position.

Lipid-induced filamentous growth in Ustilago maydis

The phytopathogenic fungus Ustilago maydis is obligately dependent on infection of maize to complete the sexual phase of its life cycle. Mating interactions between haploid, budding cells establish an infectious filamentous cell type that invades the host, induces large tumours and eventually forms large masses of black spores. The ability to switch from budding to filamentous growth is therefore critical for infection and completion of the life cycle, although the signals that influence the transition have not been identified from the host or the environment. We have found that growth in the presence of lipids promotes a filamentous phenotype that resembles the infectious cell type found in planta. In addition, the ability of the fungus to respond to lipids is dependent on both the cAMP signalling pathway and a Ras/MAPK pathway; these pathways are known to regulate mating, filamentous growth and pathogenesis in U. maydis. Overall, these results lead us to hypothesize that lipids may represent one of the signals that promote and maintain the filamentous growth of the fungus in the host environment.

Purification and characterization of a 43-kilodalton extracellular serine proteinase from Cryptococcus neoformans

An extracellular proteinase was purified from culture filtrates of Cryptococcus neoformans NHPY24 by DEAE ion-exchange chromatography and gelatin affinity column chromatography with azoalbumin as the substrate. The molecular mass of the purified enzyme was 43 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, its pH optimum was 7.0 to 8.0, and maximal activity was obtained at pH 7.5 and 37 degrees C. By isoelectric focusing, the purified enzyme had a pI of 4.77. Enzyme activity was inhibited by serine proteinase inhibitors such as phenylmethylsulfonyl fluoride and diisopropylfluorophosphate. The purified enzyme was thus a serine proteinase. It hydrolyzed natural substrates including hemoglobin, beta-casein, and gamma globulin.

Endophytic fungi associated with Mediterranean plants as a source of mycelium-bound lipases

A screening of endophytic fungi isolated from Mediterranean plants rendered a mycelium-bound lipase from a strain of Rhizopus oryzae that catalyzed the esterification of fatty acids in isooctane. The influence of various factors (water content, temperature, and pH) on ester synthesis was investigated. Catalytic activity was inversely correlated with water content. This enzyme was active over the entire pH range studied, from pH 3 to pH 8, and activity was maximal at pH 4 and pH 7. The enzyme was thermostable, with maximal activity at 60 degrees C.

Purification strategies for microbial lipases

Microbial lipases today occupy a place of prominence among biocatalysts owing to their ability to catalyze a wide variety of reactions in aqueous and non-aqueous media. The chemo-, regio- and enantio-specific behaviour of these enzymes has caused tremendous interest among scientists and industrialists. Lipases from a large number of bacterial, fungal and a few plant and animal sources have been purified to homogeneity. This has enabled their successful sequence determination and their three-dimensional structure leading to a better understanding of their unique structure-function relationships during various hydrolytic and synthetic reactions. This article presents a critical review of different strategies which have been employed for the purification of bacterial, yeast and fungal lipases. Since protein purification is normally done in a series of sequential steps involving a combination of different techniques, the effect of sequence of steps and the number of times each step is used is analyzed. This will prove to be of immense help while planning lipase purification. Novel purification technologies now available in this field are also reviewed.

Occurrence of a lipase in spores of Alternaria brassicicola with a crucial role in the infection of cauliflower leaves

Alternaria brassicicola is a pathogen that penetrates directly through the host cuticle thanks to several serine esterases, according to our findings. Among these, an 80-kDa lipase (E.C 3.1.1. 3) was detected by SDS-PAGE and immunoblotting in the water washings of ungerminated spores. The purified lipase cross-reacted with Botrytis cinerea anti-lipase antibodies, which were reported to inhibit the in vitro lipase activity. Anti-lipase antibodies were added to a conidial suspension of A. brassicicola prior to inoculation. As a result, blackspot lesions were reduced by 90% on intact cauliflower leaves, but not on leaves from which surface wax had been removed. Spore surface-bound lipase is thought to interact closely with epicuticular leaf waxes for adhesion and/or penetration of the fungal propagules during the early stages of host-parasite interactions.

A cold-adapted lipase of an Alaskan psychrotroph, Pseudomonas sp. strain B11-1: gene cloning and enzyme purification and characterization

A psychrotrophic bacterium producing a cold-adapted lipase upon growth at low temperatures was isolated from Alaskan soil and identified as a Pseudomonas strain. The lipase gene (lipP) was cloned from the strain and sequenced. The amino acid sequence deduced from the nucleotide sequence of the gene (924 bp) corresponded to a protein of 308 amino acid residues with a molecular weight of 33,714. LipP also has consensus motifs conserved in other cold-adapted lipases, i.e., Lipase 2 from Antarctic Moraxella TA144 (G. Feller, M. Thirty, J. L. Arpigny, and C. Gerday, DNA Cell Biol. 10:381-388, 1991) and the mammalian hormone-sensitive lipase (D. Langin, H. Laurell, L. S. Holst, P. Belfrage, and C. Holm, Proc. Natl. Acad. Sci. USA 90:4897-4901, 1993): a pentapeptide, GDSAG, containing the putative active-site serine and an HG dipeptide. LipP was purified from an extract of recombinant Escherichia coli C600 cells harboring a plasmid coding for the lipP gene. The enzyme showed a 1,3-positional specificity toward triolein. p-Nitrophenyl esters of fatty acids with short to medium chains (C4 and C6) served as good substrates. The enzyme was stable between pH 6 and 9, and the optimal pH for the enzymatic hydrolysis of tributyrin was around 8. The activation energies for the hydrolysis of p-nitrophenyl butyrate and p-nitrophenyl laurate were determined to be 11.2 and 7.7 kcal/mol, respectively, in the temperature range 5 to 35 degrees C. The enzyme was unstable at temperatures higher than 45 degrees C. The Km of the enzyme for p-nitrophenyl butyrate increased with increases in the assay temperature. The enzyme was strongly inhibited by Zn2+, Cu2+, Fe3+, and Hg2+ but was not affected by phenylmethylsulfonyl fluoride and bisnitrophenyl phosphate. Various water-miscible organic solvents, such as methanol and dimethyl sulfoxide, at concentrations of 0 to 30% (vol/vol) activated the enzyme.

Spectrophotometric determination of the positional specificity of nonspecific and 1,3-specific lipases

Using commercially available thiosubstrates, such as 2,3-dimercapto-1-propanol tributyrate, the regio-specificities of 1,3-specific and nonspecific lipases was confirmed. The spectrophotometric test is a simple, rapid, and convenient alternative method to those previously reported for the characterization of the positional specificities of new lipases.

Extracellular proteins of Cryptococcus neoformans and host antibody response

Proteins secreted by the fungal pathogen Cryptococcus neoformans may be involved in invasion and could be useful in vaccine design. Despite the medical importance of this fungus, little is known about its extracellular proteins or the immune response to these antigens. To study C. neoformans extracellular proteins, 12 strains were metabolically radiolabeled and protein supernatants were analyzed. Both strain- and growth condition-dependent differences were observed. Enzymatic assays of filtered culture supernatants revealed butyrate esterase and caprylate esterase lipase activity for 11 of 12 strains, as well as acid phosphatase, naphthol-AS-BI-phosphohydrolase, and beta-glucosidase activities in some strains. Serum from infected rodents immunoprecipitated several secreted proteins, consistent with in vivo expression and development of an antibody response. For strain 24067, two immunodominant species, of approximately 75 and 30 kDa, were recognized. The relative intensity of the autoradiographic bands depended on the route of infection for both rats and mice. In summary, our results indicate that (i) there are multiple proteins in C. neoformans culture supernatants, (ii) there are strain differences in supernatant protein profiles, (iii) there are differences in supernatant protein profile depending on the growth conditions, (iv) there are several new extracellular and/or cell-associated enzymatic activities, and (v) antibodies to several supernatant proteins are made in the course of infection.