title: Intracellular positioning of isoforms explains an unusually large adenylate kinase gene family in the parasite Trypanosoma brucei.
abstract: Adenylate kinases occur classically as cytoplasmic and mitochondrial enzymes, but the expression of seven adenylate kinases in the flagellated protozoan parasite Trypanosoma brucei (order, Kinetoplastida; family, Trypanosomatidae) easily exceeds the number of isoforms previously observed within a single cell and raises questions as to their location and function. We show that a requirement to target adenylate kinase into glycosomes, which are unique kinetoplastid-specific microbodies of the peroxisome class in which many reactions of carbohydrate metabolism are compartmentalized, and two different flagellar structures as well as cytoplasm and mitochondrion explains the expansion of this gene family in trypanosomes. The three isoforms that are selectively built into either the flagellar axoneme or the extra-axonemal paraflagellar rod, which is essential for motility, all contain long N-terminal extensions. Biochemical analysis of the only short form trypanosome adenylate kinase revealed that this enzyme catalyzes phosphotransfer of gamma-phosphate from ATP to AMP, CMP, and UMP acceptors; its high activity and specificity toward CMP is likely to reflect an adaptation to very low intracellular cytidine nucleotide pools. Analysis of some of the phosphotransfer network using RNA interference suggests considerable complexity within the homeostasis of cellular energetics. The anchoring of specific adenylate kinases within two distinct flagellar structures provides a paradigm for metabolic organization and efficiency in other flagellates.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, United Kingdom.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Ginger
authors.forename: E Solange
authors.initials: ES
authors.lastname: Ngazoa
authors.forename: Claudio A
authors.initials: CA
authors.lastname: Pereira
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Pullen
authors.forename: Mostafa
authors.initials: M
authors.lastname: Kabiri
authors.forename: Katja
authors.initials: K
authors.lastname: Becker
authors.forename: Keith
authors.initials: K
authors.lastname: Gull
authors.forename: Dietmar
authors.initials: D
authors.lastname: Steverding
mesh_terms: D000263:Adenylate Kinase / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D005407:Flagella / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry; D008830:Microbodies / Q000201:enzymology; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D014346:Trypanosoma brucei brucei / Q000201:enzymology*
chemical_list: D007527:Isoenzymes; D000263:Adenylate Kinase