RESUMEN
Nucleotide excision repair (NER) is responsible for the removal of a large variety of structurally diverse DNA lesions. Mutations of the involved proteins cause the xeroderma pigmentosum (XP) cancer predisposition syndrome. Although the general mechanism of the NER process is well studied, the function of the XPA protein, which is of central importance for successful NER, has remained enigmatic. It is known, that XPA binds kinked DNA structures and that it interacts also with DNA duplexes containing certain lesions, but the mechanism of interactions is unknown. Here we present two crystal structures of the DNA binding domain (DBD) of the yeast XPA homolog Rad14 bound to DNA with either a cisplatin lesion (1,2-GG) or an acetylaminofluorene adduct (AAF-dG). In the structures, we see that two Rad14 molecules bind to the duplex, which induces DNA melting of the duplex remote from the lesion. Each monomer interrogates the duplex with a ß-hairpin, which creates a 13mer duplex recognition motif additionally characterized by a sharp 70° DNA kink at the position of the lesion. Although the 1,2-GG lesion stabilizes the kink due to the covalent fixation of the crosslinked dG bases at a 90° angle, the AAF-dG fully intercalates into the duplex to stabilize the kinked structure.
Asunto(s)
Daño del ADN , Enzimas Reparadoras del ADN/química , Reparación del ADN , Proteínas de Saccharomyces cerevisiae/química , 2-Acetilaminofluoreno/química , 2-Acetilaminofluoreno/metabolismo , Secuencia de Aminoácidos , Cisplatino/química , Cisplatino/metabolismo , Cristalografía por Rayos X , Enzimas Reparadoras del ADN/genética , Enzimas Reparadoras del ADN/metabolismo , ADN de Hongos/química , ADN de Hongos/genética , ADN de Hongos/metabolismo , Modelos Moleculares , Datos de Secuencia Molecular , Conformación de Ácido Nucleico , Desnaturalización de Ácido Nucleico , Unión Proteica , Estructura Terciaria de Proteína , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Homología de Secuencia de Aminoácido , Termodinámica , Temperatura de TransiciónRESUMEN
8-Oxopurines (8-oxodG and 8-oxodA) and formamidopyrimidines (FaPydG and FaPydA) are major oxidative DNA lesions involved in cancer development and aging. Their mutagenicity is believed to result from a conformational shift of the N9-C1' glycosidic bonds from anti to syn, which allows the lesions to form noncanonical Hoogsteen-type base pairs with incoming triphosphates during DNA replication. Here we present biochemical data and what are to our knowledge the first crystal structures of carbocyclic FaPydA and FaPydG containing DNA in complex with a high-fidelity polymerase. Crystallographic snapshots show that the cFaPy lesions keep the anti geometry of the glycosidic bond during error-free and error-prone replication. The observed dG·dCâdT·dA transversion mutations are the result of base shifting and tautomerization.