Functional characterisation of the regulatory subunit of cyclic AMP-dependent protein kinase A homologue of Giardia lamblia: Differential expression of the regulatory and catalytic subunits during encystation

    Authors

    C. Gibson; B. Schanen; D. Chakrabarti;R. Chakrabarti

    Comments

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    Abbreviated Journal Title

    Int. J. Parasit.

    Keywords

    Giardia; PKA; regulatory subunit; kinase activity; localisation :; expression : encystation; I-ALPHA; SACCHAROMYCES-CEREVISIAE; CELL-DIFFERENTIATION; DICTYOSTELIUM; PATHWAY; BETA; INTESTINALIS; INHIBITOR; TRANSPORT; BIOLOGY; Parasitology

    Abstract

    To understand the functional roles of protein kinase A (PKA) during vegetative and differentiating states of Giardia parasites. we studied the structural and functional characteristics of the regulatory subunit of PKA (gPKAr) and its involvement in the giardial encystment process. Molecular cloning and characterisation showed that gPKAr contains two tandem 3'5'-cyclic adenosine monphosphate (cyclic AMP) binding domains at the C-terminal end and the interaction domain for the catalytic Subunit. A number of consensus residues including in vivo phosphorylation site for PKAc and dimerisation/docking domain are present in gPKAr. The regulatory subunit physically interacts with the catalytic subunit and inhibits its kinase activity in the absence of cyclic AMP. which could be partially restored upon addition of cyclic AMP. Western blot analysis showed a marked reduction in the endogenous gPKAr concentration during differentiation of Giardia into cysts. An increased activity of gPKAc was also detected during encystation without any significant change in the protein concentration. Distinct localisations of gPKAc to the anterior flagella, basal bodies and caudal flagella as noted in trophozoites were absent in encysting cells at later stages. Instead. PKAc staining was punctate and located mostly to the cell periphery. Our study indicates possible enrichment of the active gPKAc during late stages of encystation, which may have implications in completion of the encystment process or priming of cysts for efficient excystation. (c) 2006 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

    Journal Title

    International Journal for Parasitology

    Volume

    36

    Issue/Number

    7

    Publication Date

    1-1-2006

    Document Type

    Article

    Language

    English

    First Page

    791

    Last Page

    799

    WOS Identifier

    WOS:000238922600007

    ISSN

    0020-7519

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