title: Enzymatic mechanism controls redox-mediated protein-DNA interactions at the replication origin of kinetoplast DNA minicircles.
abstract: Kinetoplast DNA (kDNA) is the mitochondrial DNA of trypanosomatids. Its major components are several thousand topologically interlocked DNA minicircles. Their replication origins are recognized by universal minicircle sequence-binding protein (UMSBP), a CCHC-type zinc finger protein, which has been implicated with minicircle replication initiation and kDNA segregation. Interactions of UMSBP with origin sequences in vitro have been found to be affected by the protein's redox state. Reduction of UMSBP activates its binding to the origin, whereas UMSBP oxidation impairs this activity. The role of redox in the regulation of UMSBP in vivo was studied here in synchronized cell cultures, monitoring both UMSBP origin binding activity and its redox state, throughout the trypanosomatid cell cycle. These studies indicated that UMSBP activity is regulated in vivo through the cell cycle dependent control of the protein's redox state. The hypothesis that UMSBP's redox state is controlled by an enzymatic mechanism, which mediates its direct reduction and oxidation, was challenged in a multienzyme reaction, reconstituted with pure enzymes of the trypanosomal major redox-regulating pathway. Coupling in vitro of this reaction with a UMSBP origin-binding reaction revealed the regulation of UMSBP activity through the opposing effects of tryparedoxin and tryparedoxin peroxidase. In the course of this reaction, tryparedoxin peroxidase directly oxidizes UMSBP, revealing a novel regulatory mechanism for the activation of an origin-binding protein, based on enzyme-mediated reversible modulation of the protein's redox state. This mode of regulation may represent a regulatory mechanism, functioning as an enzyme-mediated, redox-based biological switch.
authors.affiliation: Department of Parasitology, Kuvin Center for the Study of Infectious and Tropical Diseases, Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
authors.forename: Dotan
authors.initials: D
authors.lastname: Sela
authors.forename: Nurit
authors.initials: N
authors.lastname: Yaffe
authors.forename: Joseph
authors.initials: J
authors.lastname: Shlomai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002453:Cell Cycle; D016831:Crithidia fasciculata / Q000235:genetics / Q000378:metabolism; D018105:DNA, Kinetoplast / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D009698:Nucleoproteins / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018741:Replication Origin / Q000235:genetics*; D014349:Trypanosoma cruzi / Q000201:enzymology / Q000235:genetics
chemical_list: D018105:DNA, Kinetoplast; D004268:DNA-Binding Proteins; D009698:Nucleoproteins; D015800:Protozoan Proteins; C095676:universal minicircle sequence binding protein, protozoan; D009247:NADH, NADPH Oxidoreductases; C049608:trypanothione reductase