NAMOT2--a redesigned nucleic acid modeling tool: construction of non-canonical DNA structures.

Using a new set of reduced coordinates developed for describing regular and unusual nucleic acid structures, we have revised our nucleic acid modeling tool NAMOT2. NAMOT2 is general in terms of modeling different nucleic acid structures. A set of modifiable libraries allows users to customize their modeling environment. With this set of libraries, NAMOT2 can be used to model non-canonical structures such as parallel-stranded, triple-stranded and quadruple-stranded nucleic acid molecules. For modeling irregular structures (junctions, hairpin loops, etc.), we introduce a structural recipe approach. The complete procedure using NAMOT2 to construct the structure of a specific molecule is treated as the recipe for that structural motif. The existing recipes can be modified to generate new recipes for different structural motifs. Several examples of nucleic acids with non-canonical structures were modeled using NAMOT2. These examples include a DNA-drug complex, a DNA cube, a six-arm junction and a curved DNA molecule.