Cisplatin GG-crosslinks within single-stranded DNA: Origin of the preference for left-handed helicity

► The antitumor drug cisplatin crosslinks two adjacent guanines of DNA. ► Pt-DNA crosslinks cause destacking of the crosslinked bases. ► In duplex DNA, the crosslinked GG dinucleotide conserves right-handed helical twist. ► In single-stranded DNA, the twist of the GG dinucleotide reverts to left-handed. ► MD simulations explain the left-handed GG twist in single-stranded Pt-DNA adducts.