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Four conserved amino acids of type IB topoisomerases (Arg130, Lys167, Arg223, and His265 in vaccinia topoisomerase) catalyze the attack by tyrosine on the scissile phosphodiester to form a DNA-(3′-phosphotyrosyl)-enzyme intermediate. The mechanism entails general acid catalysis (by Lys167 and Arg130) and transition-state stabilization (via contact of His265 with the pro-Sp oxygen). Here we query the...
Vaccinia topoisomerase IB forms a covalent DNA-(3'-phosphotyrosyl)-enzyme intermediate at its target site 5'-CCCTTp↓ in duplex DNA. The contributions of backbone electrostatics and individual phosphate oxygens to the transesterification reaction were probed by introducing 22 single Rp and Sp methylphosphonate diastereomers at 11 positions flanking the cleavage site. Methyl groups at eight positions...
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