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Molecular cloning and characterization of the Coccidioides immitis complement fixation/chitinase antigen.

ABSTRACT: Detection of anti-Coccidioides complement-fixing (CF) antibody is a valuable diagnostic and prognostic aid in coccidioidomycosis. The CF antibody response is directed against a heat-labile antigen that has chitinase activity, hereafter referred to as the CF/chitinase protein. To identify and clone this immunoreactive enzyme, we constructed a Coccidioides immitis cDNA lambda ZAP expression library from spherule RNA and detected fusion peptides expressing CF epitopes by immunoscreening. A cDNA clone consisting of 1,623 bp was identified, sequenced, and found to contain a single open reading frame that encodes a protein of 47 kDa with 427 amino acids. Deduced amino acid sequence analyses showed that the cloned CF/chitinase cDNA contains a 35-amino-acid region, beginning at Ser-18 and ending at and ending at Arg-52 which has 92% homology with the reported N-terminal amino acid sequence of authentic CF/chitinase protein. The first 17 amino acids in the deduced sequence of the cloned cDNA are not present on the mature CF/chitinase protein, suggesting that it may be a signal peptide. Expression of the CF/chitinase cDNA insert by using the pGEX-4T-3 vector yields a fusion peptide that bears CF-specific epitopes and shows chitinase activity. The CF/chitinase clone will enable large-scale production of the recombinant CF antigen for use in immunoassays and facilitate studies on the role of chitinase in the morphogenesis of C. immitis.

SUBMITTER: Yang C

PROVIDER: S-EPMC174027 | biostudies-other | 1996 Jun

REPOSITORIES: biostudies-other

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Molecular cloning and characterization of the Coccidioides immitis complement fixation/chitinase antigen.

Yang C C Zhu Y Y Magee D M DM Cox R A RA

Infection and immunity 19960601 6

Detection of anti-Coccidioides complement-fixing (CF) antibody is a valuable diagnostic and prognostic aid in coccidioidomycosis. The CF antibody response is directed against a heat-labile antigen that has chitinase activity, hereafter referred to as the CF/chitinase protein. To identify and clone this immunoreactive enzyme, we constructed a Coccidioides immitis cDNA lambda ZAP expression library from spherule RNA and detected fusion peptides expressing CF epitopes by immunoscreening. A cDNA clo ...[more]

PMID: 8675298

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Project description:A chitinase had been isolated from the culture filtrates of Coccidioides immitis endosporulating spherules and from hyphae and shown to be the coccidioidal complement fixation (CF) and immunodiffusion-CF antigen. In the present study, we made use of our previously determined amino-terminal (N-terminal) sequence of the CF-chitinase to design degenerate oligonucleotide primers and to amplify and sequence a PCR product that coded for the N-terminal portion of the CF-chitinase. The PCR product was used as a hybridization probe to screen a developing spherule-(lambda)ZAP cDNA library, and three hybridizing clones were selected. These clones were converted into their pBluescript expression plasmid form in Escherichia coli and induced to express their recombinant proteins. Lysate from only one clone, pCTS 4-2A, yielded an enzymatically functional CF-chitinase and a line of identity with control immunodiffusion-CF-positive antigen. The pCTS 4-2A insert was sequenced and found to contain a deduced open reading frame coding for a 427-amino-acid polypeptide with an approximate molecular weight of 47 kDa. When purified by a chitin adsorption-desorption method, the recombinant protein exhibited virtually identical characteristics to those of the original C. immitis CF-chitinase. Nondenaturing gels of the pCTS 4-2A E. coli lysates and the purified C. immitis and recombinant CF-chitinase revealed proteins that had chitinase activity and similar relative electrophoretic mobilities. The appearance and relative levels of hybridizing RNA from the developing spherules-endospores (SEs) and hyphae correlated with the appearance or presence and level of CF-chitinase enzyme activity found in SEs culture filtrate and in cellular extracts of developing SE and hyphae. Thus, a functional recombinant CF-chitinase antigen was produced in E. coli and was used in serological diagnostic applications. These results also suggest a functional role for this chitinase in SE development and maturation.

Project description:Results of earlier investigations have indicated that the saprobic phase of Coccidioides immitis produces a heat-stable, 19-kDa antigen with serine proteinase activity which has been suggested to be specific for this pathogenic fungus. In the present study we have determined the N-terminal and partial internal amino acid sequences of the purified, 19-kDa antigen, cloned the gene which encodes this polypeptide, and confirmed that the secreted proteinase is a Coccidioides-specific antigen (CS-Ag). Both the genomic and cDNA sequences are reported and reveal that the csa gene which encodes this antigen has no introns. A 543-bp open reading frame encodes a 181-amino-acid-containing protein with a predicted molecular mass of 19.8 kDa and an isoelectric point of 8.3. The csa gene was localized on chromosome I of three representative C. immitis clinical isolates on the basis of Southern hybridizations. Expression of the csa gene in Escherichia coli using the pET21a plasmid vector yielded a recombinant protein that was recognized in immunoblot assays by antibody raised to the purified 19-kDa CS-Ag. Secretion of the native antigen is suggested to occur by cleavage of a putative 23-residue signal peptide. The native CS-Ag showed a low degree of glycosylation. Analysis of the carbohydrate composition of the CS-Ag revealed xylose, mannose, galactose, and glucose. However, the purified antigen showed no affinity for concanavalin A. A PCR method with specificity and high sensitivity for detection of C. immitis genomic DNA, using a pair of synthetic oligonucleotide primers whose sequences were based on that of the csa gene, was developed. A 520-bp product was amplified only when C. immitis genomic DNA was used as the template. The lower limits of DNA detection using this PCR method were 1 pg of C. immitis genomic DNA by ethidium bromide staining and 100 fg after Southern hybridization. The csa gene-based PCR method for detection of C. immitis DNA is useful for culture identification and may have clinical applications for the diagnosis of coccidioidal infections.

Dataset Information

Molecular cloning and characterization of the Coccidioides immitis complement fixation/chitinase antigen.

Publications

Molecular cloning and characterization of the Coccidioides immitis complement fixation/chitinase antigen.

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