T. Seshadri, M. Viswamitra
Oct 1, 1974
Citations
0
Influential Citations
4
Citations
Journal
Pramana
Abstract
The crystal structure of deoxyguanosine (5′) phosphate, disodium salt, (5′-dGMP Na2 4H2O) has been determined from three dimensional single crystal x-ray data collected by multiple film, equi-inclination, Weissenberg method using CuKa radiation. The crystal belongs to the monoclinic space groupP21 witha=16.002±0.003 Å,b=10.730±0.003 Å,c=5.575±0.005 Å andβ=101.9°. The structure was solved by symbolic addition method using the program Multan, the reliability index being 0.090. The guanine base is in the usualanti conformation about the C (1′)-N (9) bond withxCN=52.3°. The structure shows two unique conformational features not observed in any nucleotide structure reported so far. The deoxyribose moiety shows O (1′)endo puckering with respect to the best four atom plane defined by C(1′)-C(2′)-C(3′)-C(4′). The conformation about the C(4′)-C(5′) bond isgauche-trans with ø00=62.5° and øoc=174.8°. This is the first nucleotide structure where agt conformer similar to that found in the Watson-Crick double helical DNA model has been experimentally observed. These two conformational features have also direct relevance to the concept of ‘a conformationally rigid nucleotide unit’ developed by Sundaralingam. The nine membered guanine ring is essentially planar. Bases of molecules related by a ‘c’ cell translation tend to overlap, the shortest distance being 3.51 Å between the atoms N (3) and C(8). One of the sodium atoms Na(1) has an octahedral coordination with four water oxygens and O(6) and O(3′) atoms occupying the corners at distances ranging from 2.35 Å to 2.55 Å.