The previously developed particle mesh Ewald method is reformulated in terms of efficient B-spline interpolation of the structure factors. This reformulation allows a natural extension of the method to potentials of the form 1/r p with pу1. Furthermore, efficient calculation of the virial tensor follows. Use of B-splines in place of Lagrange interpolation leads to analytic gradients as well as a significant improvement in the accuracy. We demonstrate that arbitrary accuracy can be achieved, independent of system size N, at a cost that scales as N log(N). For biomolecular systems with many thousands of atoms this method permits the use of Ewald summation at a computational cost comparable to that of a simple truncation method of 10 Å or less.

No abstract

An all-atom 5 nanosecond molecular dynamics simulation of a water-solvated micelle containing 60 sodium dodecyl sulfate monomers was performed. Structural properties such as the radius of gyration, eccentricity, micellar size, accessible surface area, dihedral angle distribution, carbon atom distribution, and the orientation of the monomers toward the micelle center of mass were evaluated. The results indicate a stable micellar system over the duration of the simulation. Evaluation of the structure and motion of the sodium counterions show (1) a long equilibration time (1 nanosecond) is required to achieve a stable distribution of counterions and (2) approximately 25% of the sodium ions are located in the first shell and 50% are located in the first two shells of the micelle during the course of the simulation. The structure of the micelle oxygen-sodium ion radial distribution function reveals two distinct peaks which divide the counterions into those close to the micelle (first shell) those far from the micelle (bulk) and those between (second shell). Finally, values of the diffusion coefficient for sodium ions followed a decreasing trend for ions in the bulk of the micellar system (D ) 1.9 × 10 -5 cm 2 /s), ions in the second shell of the micelle (D ) 1.4 × 10 -5 cm 2 /s), and those in the first shell of the micelle (D ) 1.0 × 10 -5 cm 2 /s).

Oxidative stress promotes genomic instability and human diseases1. A common oxidized nucleoside is 8-oxo-7,8-dihydro-2’-deoxyguanosine found both in DNA (8-oxo-G) and as a free nucleotide (8-oxo-dGTP)2,3. Nucleotide pools are especially vulnerable to oxidative damage4. Therefore cells encode an enzyme (MutT/MTH1) that removes free oxidized nucleotides. This cleansing function is required for cancer cell survival5,6 and to modulate E. coli antibiotic sensitivity in a DNA polymerase (pol)-dependent manner7. How polymerase discriminates between damaged and non-damaged nucleotides is not well understood. This analysis is essential given the role of oxidized nucleotides in mutagenesis, cancer therapeutics, and bacterial antibiotics8. Even with cellular sanitizing activities, nucleotide pools contain enough 8-oxo-dGTP to promote mutagenesis9,10. This arises from the dual coding potential where 8-oxo-dGTP(anti) base pairs with cytosine (Cy) and 8-oxodGTP(syn) utilizes its Hoogsteen edge to base pair with adenine (Ad)11. Here we utilized time-lapse crystallography to follow 8-oxo-dGTP insertion opposite Ad or Cy with human DNA pol β, to reveal that insertion is accommodated in either the syn- or anti-conformation, respectively. For 8-oxo-dGTP(anti) insertion, a novel divalent metal relieves repulsive interactions between the adducted guanine base and the triphosphate of the oxidized nucleotide. With either templating base, hydrogen bonding interactions between the bases are lost as the enzyme reopens after catalysis, leading to a cytotoxic nicked DNA repair intermediate. Combining structural snapshots with kinetic and computational analysis reveals how 8-oxodGTP utilizes charge modulation during insertion that can lead to a blocked DNA repair intermediate.