Searle M S, Hall J G, Denny W A, Wakelin L P
Molecular Pharmacology Group and NMR Facility, Peter MacCallum Cancer Institute, Melbourne, Vic., Australia.
Biochem J. 1989 Apr 15;259(2):433-41. doi: 10.1042/bj2590433.
1H- and 31P-n.m.r. spectroscopy were used to characterize the solution structure of the 1:1 complex formed between the antitumour antibiotic luzopeptin and the self-complementary hexanucleotide d(5'-GCATGC)2. Eighteen nuclear Overhauser effects between antibiotic and nucleotide protons, together with ring-current-induced perturbations to base-pair and quinoline 1H resonances, define the position and orientation of the bound drug molecule. Luzopeptin binds in the minor groove of the DNA with full retention of dyad symmetry, its quinoline chromophores intercalating at the 5'-CpA and 5'-TpG steps and its depsipeptide ring spanning the central two A.T base-pairs. The chromophores stack principally on the adenine base with their carbocyclic rings pointing towards the deoxyribose of the cytosine. There is no evidence for Hoogsteen base-pairing in the complex, all glycosidic bond angles and sugar puckers being typical of B-DNA as found for the free hexanucleotide. The 'breathing' motions of the A.T and internal G.C base-pairs are substantially slowed in the complex compared with the free DNA, and the observation that two phosphate resonances are shifted downfield by at least 0.5 p.p.m. in the 31P-n.m.r. spectrum of the complex suggests pronounced local helix unwinding at the intercalation sites. The data are consistent with a model of the complex in which luzopeptin bisintercalates with its depsipeptide essentially in the conformation found in the crystal of the free antibiotic [Arnold & Clardy (1981) J. Am. Chem. Soc. 103, 1243-1244]. We postulate only one conformational change within the peptide ring, which involves rotation of the pyridazine-glycine amide group linkage by 90 degrees towards the DNA surface. This manoeuvre breaks the glycine-to-glycine transannular hydrogen bonds and enables the glycine NH groups to bond to the thymine O-2 atoms of the sandwiched A.T base-pairs. It also shortens the major axis of the depsipeptide so that the interchromophore distance is more suitable for spanning two base-pairs. The model further implies that the carboxy and hydroxy groups of the L-beta-hydroxyvaline residue are appropriately positioned for hydrogen-bonding to the 2-amino group of guanine and the O-2 atom of cytosine of the adjacent G.C base-pair.
利用1H和31P核磁共振光谱对抗肿瘤抗生素鲁佐肽与自互补六核苷酸d(5'-GCATGC)2形成的1:1复合物的溶液结构进行了表征。抗生素与核苷酸碱基质子之间有18个核Overhauser效应，以及环电流对碱基对和喹啉1H共振的扰动，确定了结合药物分子的位置和取向。鲁佐肽结合在DNA的小沟中，二元对称性完全保留，其喹啉发色团在5'-CpA和5'-TpG步插入，其缩肽环跨越中央两个A.T碱基对。发色团主要堆积在腺嘌呤碱基上，其碳环指向胞嘧啶的脱氧核糖。复合物中没有Hoogsteen碱基配对的证据，所有糖苷键角和糖的褶皱都是游离六核苷酸中典型的B-DNA特征。与游离DNA相比，复合物中A.T和内部G.C碱基对的“呼吸”运动显著减慢，并且在复合物的31P核磁共振谱中观察到两个磷酸共振向下场移动至少0.5 ppm，这表明在插入位点有明显的局部螺旋解旋。这些数据与复合物的模型一致，其中鲁佐肽双插入，其缩肽基本上处于游离抗生素晶体中发现的构象[阿诺德和克拉迪(1981年)《美国化学会志》103，1243 - 1244]。我们假设肽环内只有一个构象变化，即哒嗪 - 甘氨酸酰胺基团的连接向DNA表面旋转90度。这个操作打破了甘氨酸到甘氨酸的跨环氢键，并使甘氨酸的NH基团与夹心A.T碱基对的胸腺嘧啶O - 2原子结合。它还缩短了缩肽的长轴，使得发色团间的距离更适合跨越两个碱基对。该模型进一步表明，L-β-羟基缬氨酸残基的羧基和羟基位置适当，可与相邻G.C碱基对的鸟嘌呤2 - 氨基和胞嘧啶的O - 2原子形成氢键。
