A (6-4) Photolyase Model: Repair of DNA (6-4) Lesions Requires a Reduced and Deprotonated Flavin

Abstract

Ultraviolet irradiation of cells causes the formation of a variety of DNA lesions with known mutagenic, carcinogenic, and lethal effects. [1,2] The main UV lesions are cyclobutane ± pyrimidine dimers (CPD lesions) formed in a photochemically allowed [2p 2p] cycloaddition and (6-4) photoadducts; the latter are presumably more mutagenic. [3,4] The highly mutagenic (6-4) lesions are believed to be formed in a Paterno ¬ -B¸chi reaction between two adjacent pyrimidines in the DNA duplex to give initially an oxetane intermediate, which rearranges above À 80 8C to the (6-4) photoadduct by a proton shift and a CÀO bond scission (Scheme 1). [5] Both types of DNA lesions are repaired in many organisms by a special class of repair enzymes, namely DNA photolyases, which cleave both lesions back into the monomers in a lightdependent, single electron transfer based repair reaction. [6] In the last decade, crystallographic, [7, 8] enzymatic, [9, 10] and model compound studies [11±14] showed that the photolyases, [15] which are responsible for the repair of CPD lesions, contain a[5] K.[17] Initial synthesis of 1: A solution of 1,3,5-tris(diphenylphosphanyl)benzene (L; 63 mg, 0.1 mmol) in CH 2 Cl 2 (3 mL) was added to a solution of AgOTf (38.5 mg, 0.15 mmol) in CH 3 NO 2 (1 mL). Diffusion of diethyl ether vapor into the resulting solution over one week gave colorless hexagonal crystals of 1 in 10 % yield, together with powdery amorphous material. Higher yield synthesis: 1,3,5-tris(diphenylphosphanyl)benzene (L; 31.5 mg, 0.05 mmol) and AgOTf (17.0 mg, 0.067 mmol) were dissolved in a mixture of ethanol (7 mL) and nitromethane (3 mL), placed in a loosely stoppered polypropylene flask and partially evaporated at 88 8C overnight. Block and hexagonal colorless crystals were manually separated from the powdery amorphous byproduct. Yield: 50 ± 80 %; elemental analysis calcd (%) for [Ag 4 L 3 (OTf) 4 ] ¥ CH 3 NO 2 : C 52.79, H 3.42; found: C 52.55, H 3.32. [18] X-ray data were collected on a BrukerAXS SMART diffractometer using the SAINT-NT [26] software with omega/phi scans. A crystal was mounted on to the diffractometer under dinitrogen at approximately 120 K. The structure was solved using direct methods with the SHELXTL program package. [27] Crystal Data for the hexagonal plate crystals {C 130 H 99 F 12 Ag 4 P 9 S 4 O 12 } n (1): M 2919.54, hexagonal, space group P3 ≈ c, a 29.949(8), c 25.929(10) ä, V 20 141(11) ä À3 , Z 4, m 0.545 mm À1 . A total of 39 337 reflections were measured for the angle range 4 < 2q < 45 and 8797 independent reflections were used in the refinement. The final parameters were wR2 0.3009 and R1 0.0906 [I > 2sI]. Cell parameters for the block crystals [{C 130 H 99 F 12 Ag 4 -P 9 S 4 O 12 } n ] (1') [23] : M 2919.54, hexagonal, space group P3 ≈ c, a 30.076(1), c 25.791(1) ä, V 20 204(1) ä À3 . The residual densities (< 1 electron ä À3 ) associated with the voids indicate small amounts of very diffuse solvent molecules. Consequently, the nature of the solvent could not be determined using X-ray diffraction m...

Do Photolyases Need To Provide Considerable Activation Energy for the Splitting of Cyclobutane Pyrimidine Dimer Radical Anions?

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Solid‐Phase Synthesis of Acid‐Sensitive N‐(2‐Aminoethyl)glycine‐PNA Oligomers by the Fmoc/Bhoc Strategy

“…The alternative regioisomer was not observed 20. The thymineoxetane acetic acid was purified by precipitation and obtained in 28 % yield 21…”

Repair of (6‐4) Lesions in DNA by (6‐4) Photolyase: 20 Years of Quest for the Photoreaction Mechanism

“…The idea of photoenzymatic splitting of a preformed oxetane intermediate was supported by studies of model compounds bearing an isoalloxazine and an oxetane attached to thymine derivatives. Illumination of such model compounds under reductive conditions resulted indeed in splitting of the oxetane ring .…”