This subgroup contains the families of proteins that form part of the biosynthetic pathways of Factor420 (F420) in the form of FO Synthase, and menaquinone (vitamin K2). Both perform complex ring formations and are members of the radical S-adenosylmethionine (AdoMet) superfamily of proteins.
In the case of the menaquinone synthase enzymes, both the mechanisms of the two enzymes and role of the SAM moiety have been proposed. In mqnC, SAM is stoichiometric, and generates methionine and deoxyadenosine. In mqnE, the deoxyadeonsine moiety is added to the chorismate substrate. Thus, in both cases SAM is stoichometric.
Petersen JL, Ronan PJ
Critical role of 7,8-didemethyl-8-hydroxy-5-deazariboflavin for photoreactivation in Chlamydomonas reinhardtii
▸ Abstract
DNA photolyases use two noncovalently bound chromophores to catalyze photoreactivation, the blue light-dependent repair of DNA that has been damaged by ultraviolet light. FAD is the catalytic chromophore for all photolyases and is essential for photoreactivation. The identity of the second chromophore is often 7,8-didemethyl-8-hydroxy-5-deazariboflavin (FO). Under standard light conditions, the second chromophore is considered nonessential for photoreactivation because DNA photolyase bound to only FAD is sufficient to catalyze the repair of UV-damaged DNA. phr1 is a photoreactivation-deficient strain of Chlamydomonas. In this work, the PHR1 gene of Chlamydomonas was cloned through molecular mapping and shown to encode a protein similar to known FO synthases. Additional results revealed that the phr1 strain was deficient in an FO-like molecule and that this deficiency, as well as the phr1 photoreactivation deficiency, could be rescued by transformation with DNA constructs containing the PHR1 gene. Furthermore, expression of a PHR1 cDNA in Escherichia coli produced a protein that generated a molecule with characteristics similar to FO. Together, these results indicate that the Chlamydomonas PHR1 gene encodes an FO synthase and that optimal photoreactivation in Chlamydomonas requires FO, a molecule known to serve as a second chromophore for DNA photolyases.
Hiratsuka T, Furihata K, Ishikawa J, Yamashita H, Itoh N, Seto H, Dairi T
An alternative menaquinone biosynthetic pathway operating in microorganisms
▸ Abstract
In microorganisms, menaquinone is an obligatory component of the electron-transfer pathway. It is derived from chorismate by seven enzymes in Escherichia coli. However, a bioinformatic analysis of whole genome sequences has suggested that some microorganisms, including pathogenic species such as Helicobacter pylori and Campylobacter jejuni, do not have orthologs of the men genes, even though they synthesize menaquinone. We deduced the outline of this alternative pathway in a nonpathogenic strain of Streptomyces by bioinformatic screening, gene knockouts, shotgun cloning with isolated mutants, and in vitro studies with recombinant enzymes. As humans and commensal intestinal bacteria, including lactobacilli, lack this pathway, it represents an attractive target for the development of chemotherapeutics.
Menaquinone Biosynthesis: Formation of Aminofutalosine Requires a Unique Radical SAM Enzyme
▸ Abstract
Menaquinone (MK, vitamin K2) is a lipid-soluble molecule that participates in the bacterial electron transport chain. In mammalian cells, MK functions as an essential vitamin for the activation of various proteins involved in blood clotting and bone metabolism. Recently, a new pathway for the biosynthesis of this cofactor was discovered in Streptomyces coelicolor A3(2) in which chorismate is converted to aminofutalosine in a reaction catalyzed by MqnA and an unidentified enzyme. Here, we reconstitute the biosynthesis of aminofutalosine and demonstrate that the missing enzyme (aminofutalosine synthase, MqnE) is a radical SAM enzyme that catalyzes the addition of the adenosyl radical to the double bond of 3-[(1-carboxyvinyl)oxy]benzoic acid. This is a new reaction type in the radical SAM superfamily.
J Am Chem Soc
2013;135(41):15318-15321
| PubMed ID:
24083939
Cooper LE, Fedoseyenko D, Abdelwahed SH, Kim SH, Dairi T, Begley TP
In Vitro Reconstitution of the Radical S-Adenosylmethionine Enzyme MqnC Involved in the Biosynthesis of Futalosine-Derived Menaquinone
▸ Abstract
The radical S-adenosylmethionine enzyme MqnC catalyzes conversion of dehypoxanthine futalosine (DHFL) to the unique spiro compound cyclic DHFL in the futalosine pathway for menaquinone biosynthesis. This study describes the in vitro reconstitution of [4Fe-4S] cluster-dependent MqnC activity and identifies the site of abstraction of a hydrogen atom from DHFL by the adenosyl radical.
Annu Rev Biochem
2013;52(27):4592-4594
| PubMed ID:
23763543
