PDB entry: 4u5m

The iconic double helical structure of B-form DNA needs no introduction, but DNA can take on several different structures too. G-quadruplex DNA is formed from guanine-rich DNA sequences which are found in the telomeres. 

While G-quadruplexes vary much in structure, so far all have been right-handed. In this week's release of the PDB however, the first structure of a left-handed G-quadruplex is seen.

The work is descibed by Ching et al. in PNAS. DOI:10.1073/pnas.1418718112