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Molecular cloning and characterization of Coccidioides immitis antigen 2 cDNA.

ABSTRACT: Previous experiments have provided evidence that Coccidioides immitis antigen 2 (Ag2) is a major T-cell-reactive component of mycelia and spherule cell walls. Here we report the identification and cloning of the cDNA that encodes Ag2 from a lambda ZAP cDNA expression library constructed from spherule-derived RNA. DNA sequence analysis established that the 1,255-bp clone contains a 174-bp 5' untranslated region, a 582-bp open reading frame which encodes for a protein consisting of 194 amino acids, and a 375-bp 3' untranslated region, including a poly(A) tail. The recombinant Ag2 protein has a predicted molecular mass of 19.5 kDa and contains an 18-amino-acid N terminus which has been tentatively identified as a signal peptide. The Ag2 cDNA was ligated into the pGEX-4T-3 vector and expressed in Escherichia coli TG-1 cells as a glutathione S-transferase fusion protein. The recombinant fusion protein showed reactivity with sera from patients with coccidioidomycosis and elicited delayed-type footpad hypersensitivity responses in Coccidioides-immune mice. These results suggest that the Ag2 cDNA can be used for the large-scale production of this immunologically important protein.

SUBMITTER: Zhu Y

PROVIDER: S-EPMC174128 | biostudies-other | 1996 Jul

REPOSITORIES: biostudies-other

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Molecular cloning and characterization of Coccidioides immitis antigen 2 cDNA.

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

Infection and immunity 19960701 7

Previous experiments have provided evidence that Coccidioides immitis antigen 2 (Ag2) is a major T-cell-reactive component of mycelia and spherule cell walls. Here we report the identification and cloning of the cDNA that encodes Ag2 from a lambda ZAP cDNA expression library constructed from spherule-derived RNA. DNA sequence analysis established that the 1,255-bp clone contains a 174-bp 5' untranslated region, a 582-bp open reading frame which encodes for a protein consisting of 194 amino acids ...[more]

PMID: 8698497

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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.

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.

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Molecular cloning and characterization of Coccidioides immitis antigen 2 cDNA.

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Molecular cloning and characterization of Coccidioides immitis antigen 2 cDNA.

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