Investigations on unconventional hydrogen bonds in RNA binding proteins: The role of CH⋯OC interactions

Influence of C-H...O interactions on the structural stability of β-lactamases

β-Lactamases produced by pathogenic bacteria cleave β-lactam antibiotics and render them ineffective. Understanding the principles that govern the structural stability of β-lactamases requires elucidation of the nature of the interactions that are involved in stabilization. In the present study, we systematically analyze the influence of CH...O interactions on determining the specificity and stability of β-lactamases in relation to environmental preferences. It is interesting to note that all the residues located in the active site of β-lactamases are involved in CH...O interactions. A significant percentage of CH...O interactions have a higher conservation score and short-range interactions are the predominant type of interactions in β-lactamases. These results will be useful in understanding the stability patterns of β-lactamases.

Synthesis and crystallographic analysis of 5-Se-thymidine DNAs

We investigated the possibility of the interaction of 5-CH(3) of thymidine and its 5'-phosphate backbone (C-H...O(-)-PO(3) interaction) in DNA via the insertion of the atomic probe (a selenium atom) into the exo-5-position of thymidine (5-Se-T). 5-Se-T was synthesized for the first time, via Mn(OAc)(3) assisted electrophilic addition of CH(3)SeSeCH(3) to 3',5'-di-O-benzoyl-2'-deoxyuridine. The 5-Se-T phosphoramidite was subsequently synthesized and incorporated into DNA in over 99% coupling yield. Biophysical and structural investigations of the 5-Se-T DNAs revealed that the Se-modified and nonmodified DNAs are virtually identical. In addition, the crystallographic analysis of a 5-Se-T DNA strongly suggests a hydrogen-bond formation between the 5-CH(3) and 5'-phosphate groups (CH(3)...PO(4)(-) interaction).