title: Multiple splice variants encode a novel adenylyl cyclase of possible plastid origin expressed in the sexual stage of the malaria parasite Plasmodium falciparum.
abstract: We report the characterization of an unusual adenylyl cyclase gene from Plasmodium falciparum, here designated PfACalpha. The level of mRNA expression is maximum during development of gametocytes (the sexual blood stage of the parasite life cycle). The gene is highly interrupted by 22 introns, and reverse transcriptase-PCR analysis revealed that there are multiple mRNA splice variants. One intron has three alternative 3'-splice sites that confer the potential to encode distinct forms of the enzyme using alternative start codons. Deduced amino acid sequences predict membrane-spanning regions, the number of which can vary between two and six depending on the splice variant. Expression of a synthetic form of two of these variants in Xenopus oocytes and in Dictyostelium adenylyl cyclase-deficient mutants, confirms that PfACalpha is a functional adenylyl cyclase. These results identify a novel mechanism in P. falciparum for the generation of multiple isoforms of a key, membrane-bound signaling molecule from a single genomic copy. Comparisons of the catalytic domains of PfACalpha and a second putative P. falciparum adenylyl cyclase (PfACbeta) with those from other species reveal an unexpected similarity with adenylyl cyclases from certain prokaryotes including the cyanobacteria (blue green algae). In addition, the presence of an unusual active site substitution in a position that determines substrate specificity, also characteristic of these prokaryotic forms of the enzyme, further suggests a plastid origin for the Plasmodium cyclases.
authors.affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, United Kingdom.
authors.forename: David K
authors.initials: DK
authors.lastname: Muhia
authors.forename: Claire A
authors.initials: CA
authors.lastname: Swales
authors.forename: Ursula
authors.initials: U
authors.lastname: Eckstein-Ludwig
authors.forename: Shweta
authors.initials: S
authors.lastname: Saran
authors.forename: Spencer D
authors.initials: SD
authors.lastname: Polley
authors.forename: John M
authors.initials: JM
authors.lastname: Kelly
authors.forename: Pauline
authors.initials: P
authors.lastname: Schaap
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Krishna
authors.forename: David A
authors.initials: DA
authors.lastname: Baker
mesh_terms: D000262:Adenylyl Cyclases / Q000737:chemistry* / Q000378:metabolism; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D020134:Catalytic Domain; D003001:Cloning, Molecular; D018387:Codon, Initiator; D000458:Cyanobacteria / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004023:Dictyostelium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019143:Evolution, Molecular; D005091:Exons; D007438:Introns; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010802:Phylogeny; D010963:Plasmodium falciparum / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014981:Xenopus; D014982:Xenopus laevis
chemical_list: D018387:Codon, Initiator; D012333:RNA, Messenger; D004247:DNA; D000242:Cyclic AMP; D000262:Adenylyl Cyclases