Refined Structure of the Doubly Intercalated d(TAT^AFBGCATA)₂ Aflatoxin B₁ Adduct

Abstract

The refined solution structure for the 8, 9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 adduct was refined from the oligodeoxynucleotide duplex d(TATAFBGCATA)2 using a molecular dynamics protocol restrained by NOE data obtained from 1H NMR and compared with the refined structure of the unmodified oligomer, d(TATGCATA)2. The two aflatoxin B1 (AFB1) moieties were symmetry related by the pseudodyad axis of the self-complementary oligodeoxynucleotide. Each AFB1 intercalated into the helix above the 5'-face of the modified guanine, corroborating NMR spectroscopic data [Gopalakrishnan, S., Harris, T. M., and Stone, M. P. (1990) Intercalation of Aflatoxin B1 in Two Oligodeoxynucleotide Adducts: Comparative 1H NMR Analysis of d(ATCAFBGAT).d(ATCGAT) and d(ATAFBGCAT)2 Biochemistry 29, 10438-10448]. Molecular dynamics calculations restrained with 292 experimentally and empirically derived distances refined a family of structures characterized by pairwise root mean square differences of <1.3 A. Complete relaxation matrix calculations yielded a sixth root residual of 11 x 10(-2). Comparison of the refined structure with that of the corresponding unmodified oligodeoxynucleotide suggested that the two AFB1 adducts introduced a perturbation of the DNA localized at the two sites of adduction. The calculations predicted that each adduct introduced a "kink" into the DNA helical axis. However, the pseudodyad symmetry relating the two intercalation sites resulted in no net bending of the DNA. The results suggest the possibility that AFB1 lesions at adjacent guanines in the 5'-GC-3' sequence may be recognized or processed differently than are isolated AFB1 lesions.

The aflatoxin B 1 formamidopyrimidine adduct plays a major role in causing the types of mutations observed in human hepatocellular carcinoma

“…In addition there is a possible hydrogen bond between the formyl proton of what is thought to be FAPY major and the exocyclic amino group on a neighboring adenine. The NMR solution structure of AFB 1 -N7-Gua also reveals an increased melting temperature of the DNA duplex, but only by about 3-5°C (42). Additionally, this form of the adduct bends slightly the DNA helix (28).…”

“…In support of this view, excision repair systems preferentially remove AFB 1 -N7-Gua from the DNA of human fibroblasts (43). The FAPY adduct, having a more subtle effect on DNA architecture and a more profound effect on the local melting temperature of the DNA duplex than AFB 1 -N7-Gua (29,41,42), may evade repair, which is in line with its persistence in vivo. The longevity of the FAPY adduct, combined with its high mutagenic potential, makes it a dangerous lesion.…”

Thermal stabilization of the DNA duplex by adducts of aflatoxin B1

“…Moreover, the FAPY major adduct blocked replication bypass. 33 The availability of site-specifically modified oligodeoxynucleotides allowed biophysical characterization of both the guanine N7 cationic 23,[41][42][43] and FAPY 34 major AFB 1 adducts. The cationic adduct induced small but measurable increases in thermal stability of the DNA duplex.…”

A Review of the Role of Mitochondrial Manganese Superoxide Dismutase in Human Disorders, such as, Diabetes

“…Physically the SOD-2 gene consists of 5 exons and 4 introns [16]. In all the species studied there are no TATA or CAAT boxes identified but the GCrich regions are present in all species [17,18]. There are putative NF-κB transcription regulatory elements in the human and mouse genes.…”