Abstract
Leishmania parasites are exposed to pronounced changes in their environment during their life cycle as they migrate from the sandfly midgut to the insect proboscis and then into the phagolysosomes of the vertebrate macrophages. The developmental transformations that produce each life cycle stage of the parasite may be signaled in part by binding of environmental ligands to receptors which mediate transduction of extracellular signals. We have identified a family of five clustered genes in Leishmania donovani which may encode signal transduction receptors. The coding regions of two of these genes, designated rac-A and rac-B, have been sequenced and shown to code for proteins with an NH2-terminal hydrophilic domain, an intervening putative transmembrane segment, and a COOH-terminal domain that has high sequence identity to the catalytic domain from adenylate cyclases in other eukaryotes. We have expressed the receptor-adenylate cyclase protein (RAC)-A protein in Xenopus oocytes and demonstrated that it functions as an adenylate cyclase. Although RAC-B exhibits no catalytic activity when expressed in oocytes, co-expression of RAC-A and RAC-B negatively regulates the adenylate cyclase activity of RAC-A, suggesting that these two proteins interact in the membrane. Furthermore, a truncated version of RAC-A functions as a dominant negative mutant that inhibits the catalytic activity of the wild type receptor. The rac-A and rac-B genes encode developmentally regulated mRNAs which are expressed in the insect stage but not in the mammalian host stage of the parasite life cycle.
Highlights
From the Wepartment of Molecular Microbiology and Immunology and the §Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201
We demonstrate that L. donovani parasites contain a family of genes that encode putative receptor-adenylate cyclases (RACs)l that are structurally very similar to the predicted proteins described in T. brucei and T. equiperdum
Cloning and Sequencing of Adenylate Cyclase Genes from Leishmania donovani-A PCR-based strategy was used to clone receptor-adenylate cyclase genes from L. donovani based on the assumption that they would contain sequences related to those found in the highly conserved catalytic domains of the trypanosome proteins [9, 10]
Summary
Leishmania parasites are exposed to pronounced changes in their environment during their life cycle as they migrate from the sandtly midgut to the insect proboscis and into the phagolysosomes of the vertebrate macrophages. The developmental transformations that produce each life cycle stage of the parasite may be signaled in part by binding of environmental ligands to receptors which mediate transduction of extracellular signals. The rae-A and rac-B genes encode developmentally regulated mRNAs which are expressed in the insect stage but not in the mammalian host stage of the parasite life cycle. P. K) from the National Institutes of Health, and by a New Investigator Award in Molecular Parasitology The costs of publication of this article were defrayed in part by the payment of page charges. The nucleotide sequencers) reported in this paper has been submitted to the GenBank TM / EMBL Data Bank with accession numberts) U17042 and U17043
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
