Singh, IshaKim, Myong JungMolt, Robert W.Hoshika, ShuichiBenner, Steven A.Georgiadis, Millie M.2019-06-122019-06-122017-11-17Singh, I., Kim, M. J., Molt, R. W., Hoshika, S., Benner, S. A., & Georgiadis, M. M. (2017). Structure and Biophysics for a Six Letter DNA Alphabet that Includes Imidazo[1,2-a]-1,3,5-triazine-2(8H)-4(3H)-dione (X) and 2,4-Diaminopyrimidine (K). ACS synthetic biology, 6(11), 2118–2129. doi:10.1021/acssynbio.7b00150https://hdl.handle.net/1805/19590A goal of synthetic biology is to develop new nucleobases that retain the desirable properties of natural nucleobases at the same time as expanding the genetic alphabet. The nonstandard Watson-Crick pair between imidazo[1,2-a]-1,3,5-triazine-2(8H)-4(3H)-dione (X) and 2,4-diaminopyrimidine (K) does exactly this, pairing via complementary arrangements of hydrogen bonding in these two nucleobases, which do not complement any natural nucleobase. Here, we report the crystal structure of a duplex DNA oligonucleotide in B-form including two consecutive X:K pairs in GATCXK DNA determined as a host-guest complex at 1.75 Å resolution. X:K pairs have significant propeller twist angles, similar to those observed for A:T pairs, and a calculated hydrogen bonding pairing energy that is weaker than that of A:T. Thus, although inclusion of X:K pairs results in a duplex DNA structure that is globally similar to that of an analogous G:C structure, the X:K pairs locally and energetically more closely resemble A:T pairs.en-USPublisher PolicyCrystallography, X-RayDNA, B-FormOligodeoxyribonucleotidesPyrimidinesArticle