A new gene involved in coenzyme Q biosynthesis in Escherichia coli: UbiI functions in aerobic C5-hydroxylation

International audienceCoenzyme Q (ubiquinone or Q) is a redox-active lipid found in organisms ranging from bacteria to mammals in which it plays a crucial role in energy-generating processes. Q biosynthesis is a complex pathway that involves multiple proteins. In this work, we show that the uncharacterized conserved visC gene is involved in Q biosynthesis in Escherichia coli, and we have renamed it ubiI. Based on genetic and biochemical experiments, we establish that the UbiI protein functions in the C5-hydroxylation reaction. A strain deficient in ubiI has a low level of Q and accumulates a compound derived from the Q biosynthetic pathway, which we purified and characterized. We also demonstrate that UbiI is only implicated in aerobic Q biosynthesis and that an alternative enzyme catalyzes the C5-hydroxylation reaction in the absence of oxygen. We have solved the crystal structure of a truncated form of UbiI. This structure shares many features with the canonical FAD-dependent para-hydroxybenzoate hydroxylase and represents the first structural characterization of a monooxygenase involved in Q biosynthesis. Site-directed mutagenesis confirms that residues of the flavin binding pocket of UbiI are important for activity. With our identification of UbiI, the three monooxygenases necessary for aerobic Q biosynthesis in E. coli are known

Coplanar conjugated β-nitroporphyrins and some aspects of nitration of porphyrins with N\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e

Sterically controlled N2O4 nitration of a meso-2,3-unsubstituted porphyrin or a bis-α-unsubstituted pyrroloporphyrin affords coplanar conjugated β-nitroporphyrins displaying strong electronic interactions. (C) 2000 Elsevier Science Ltd

Dihydroporphyrin synthesis: New methodology

Selective formation of trans-nitrochlorins 16-19, cyclopropylchlorins 14, 15, and 20-23, or functionalized trans-chlorins 5-13 by reaction of 2- nitro-5,10,15,20-tetraphenylporphyrin 1 with \u27active\u27 methylene compounds such as malonates or malononitrile in the presence of base has been achieved. Reaction control is accomplished via sequential Michael additions, followed by intra-molecular nucleophilic displacement of a secondary nitro group. Steric as well as thermodynamic effects have been found to govern the selectivity of product formation. Ambient temperature or bulky carbanion substituents lead to nitrochlorins and/or cyclopropylchlorins. Increased reaction temperatures, combined with sterically less encumbered carbanion substituents, favor the formation of disubstituted trans-chlorins. Nucleophilic ring-opening reactions of cyclopropyl-derivative 14 afford disubstituted trans-chlorin products 5 and 25 and provide additional mechanistic evidence for the intermediacy of the cyclopropylchlorin. Use of porphyrins with modified meso-phenyl positions illustrates the generality of this methodology and allows a novel method for the preparation of a wide range of reduced porphyrins, which may find application in fields such as the photodynamic therapy (PDT) of cancer

Metal ion-induced self assembly of open-chain tetrapyrrole derivatives: Double stranded dinuclear complexes from 10-oxo-5,15-biladienes

Syntheses of double stranded neutral species via the complexation of Zn, Cd, and Hg with 10-oxo-5,15-biladiene LH2 are described. Formation of the single stranded Cd complex indicates that the self assembly process which affords the double stranded system is not simply a consequence of relief of steric strain. The crystal structure of the cadmium(II) double stranded dimer 8 is described. Long contact distances between carbonyl spacers and Cd ions in the crystal structure of and complete the coordination sphere of each Cd, concomitantly forming two distorted trigonal bipyramidal metal centers. Fast coordination/decoordination phenomena involving the carbonyl spacers and the two metallic centers in the zinc(II), cadmium(II) and mercury(II) dimeric complexes 7, 8 and 9, respectively, are investigated by using variable temperature 1H NMR. A bending/twisting process is proposed, and its associated energy barrier (40-50 kJ mol-1) is determined for the first time

Rational approach to the synthesis of meso-meso (5,5′) linked bis-porphyrins

A novel approach for the synthesis of 5,5′-directly linked metal-free bis-porphyrins is reported; McMurry type coupling of dipyrroketones (e.g. 1) leads to 1,1,2,2-tetra(2-pyrrolyl)ethene 2, which after tetra-formylation (to give 3) and MacDonald macrocyclization with a 1,9-di-unsubstituted dihydrodipyrrin 4, affords the 5,5′-bis-porphyrin 5

Oligomeric porphyrin arrays

The field of synthesis and physical characterization of oligomeric porphyrin arrays has been the subject of intense research in recent years. Some of these systems present unique physical and optical properties which reflect the extent of electronic interaction between the monomers in the array, and determines their potential applications in chemistry, physics, and biology. General synthetic approaches to a multitude of porphyrin arrays, including directly linked meso-meso, meso-β, and β-β compounds, oligoporphyrins with fused π-systems, and arrays bearing rigid or flexible spacers, developed by us and by others, are described. X-Ray structures of representative compounds are presented

Near-IR absorption of porphyrin methylcarbocations

Syntheses of stabilized meso-and β-carbocations of nickel(II) porphyrins are reported and compared. A novel dimeric porphyrin cation absorbing at 1030 nm is also described. © 2003 Elsevier Ltd. All rights reserved

A convenient synthesis of functionalized tetraphenylchlorins

Reaction of metallo-2-nitro-5,10,15,20-tetraphenylporphyrins with \u27active-methylene\u27 compounds (e.g. malonates, malononitriles) in the presence of base gives access to novel cyclopropachlorins or functionalized trans-chlorins (both characterized by X-ray crystallography) by way of a sequential Michael addition and rare nucleophilic displacement of a secondary nitro group