| ENERGY MINIMIZATION, MOLECULAR DYNAMICS | TWO STARTING STRUCTURES WITH BENZO[A]PYRENE MOIETY INSIDE THE DUPLEX AND OUTSIDE THE DUPLEX, RESPECTIVELY, WERE GENERATED BY CONNECTING A STANDARD B-TYPE DNA FRAGMENT WITH A MANUALLY BUILD (+)-DE2-[BAP] FRAGMENT. SOLUTION STRUCTURES FOR THE DUPLEX WERE GENERATED BY RESTRAINTED MOLECULAR DYNAMICS AND RESTRAINTED ENERGY MINIMIZATION USING A SET OF INTER-PROTON DISTANCE RESTRAINTS AND DIHEDRAL ANGLE RESTRAINTS WHICH WERE DERIVED FROM NMR EXPERIMENTS. SOME OF STRUCTURES WITH MINIMUM RESTRAINT VIOLATIONS WERE FURTHER REFINED BY THE ITERATIVE RELAXATION MATRIX ANALYSIS (IRMA) METHOD OVER 111 WELL-SEPARATED CROSS PEAKS IN NOESY SPECTRA RECORDED IN D2O AND MIXING TIMES OF 50, 80, 120, 160 AND 200 MS. THE STRUCTURE PRESENTED HERE WAS ONE OF THE FIVE REFINED AND MINIMIZED STRUCTURES. THE FOLLOWING RESTRAINTS WERE APPLIED IN THE MOLECULAR DYNAMICS/ENERGY MINIMIZATION CALCULATIONS. THESE WERE; (1) INTER-PROTON DISTANCE RESTRAINTS DIRECTLY DERIVED FROM NOE DATA; (2) BACKBONE DIHEDRAL ANGLE RESTRAINTS FOR A STANDARD B-DNA EXCEPT THOSE IMMEDIATELY ADJACENT TO THE MODIFIED RESIDUE; (3) DIHEDRAL ANGLE RESTRAINTS FOR ALL GLYCOSIDIC BONDS, EXCEPT MODIFIED DA RESIDUE IN THE CENTER; (4) HYDROGEN BOND RESTRAINTS (BOTH DISTANCE AND PLANARITY ) FOR ALL BASE-PAIRS EXCEPT CENTRAL DA-DG MISMATCH PAIR. THESE RESTRAINTS WERE JUSTIFIED BY THE FACT THAT THE MODIFIED DUPLEX DISPLAYED CHARACTERISTIC NMR SPECTRA OF A B-DNA EXCEPT NEAR LESION SITE, WHERE THE BAP MOIETY WAS INTERCALATED. THE MODIFIED DA RESIDUE DISPLAYED C3'-ENDO SUGAR RING AND A SYN GLYCOSIDIC BOND. IT ALSO FORMED A NON-WATSON-CRICK BASE PAIR WITH THE OPPOSITE DG. | NMRCHITECT |
