Stretching and twisting of the DNA duplexes in coarse grained dynamical models

Three coarse-grained models of the double-stranded DNA are proposed and compared in the context of mechanical manipulation such as twisting and various schemes of stretching. The models differ in the number of effective beads (between two and five) representing each nucleotide. They all show similar behavior and, in particular, lead to a torque-force phase diagrams qualitatively consistent with experiments and all-atom simulations

Determining critical amino acid contacts for knotted protein folding

Proteins with a non-trivial topological structure are currently well recognized, while a knotted protein chain represents a new motif in protein three dimensional folds. Recent comprehensive analysis of the Protein Data Base shows that knotted proteins represent 1.5% of known protein structures. Determination of a free energy landscape of knotted proteins, and its understanding provides a serious challenge for both experimentalists and theoreticians. Moreover the role of a knot for biological activity of protein still remains elusive. In this work we study the smallest knotted proteins ( PDB code 2efv) to understand/investigate their free energy landscape, by means of extensive molecular dynamics simulations. We explore the dependence of the thermodynamics, kinetics and protein folding pathways on the native-likes contact maps and on the length of the chain. We analyze two sets of native-like contacts , which differ by a number of long range interactions, and we consider the 2efv protein with two different lengths of its C-terminus end. We identify the subset of native contacts sufficient to explore the entire free energy landscape. Then, we analyze the influence of the remaining set of native contacts – we show that the set of additional contacts may enhance folding kinetics, and that it has an influence on folding pathways