Green fluorescent protein (GFP) is a light-emitting protein that does not require a prosthetic group for its fluorescent activity. As such, GFP has become indispensable as a molecular tool in molecular biology. Nonetheless, there has been no subatomic elucidation of the GFP structure owing to the structural polymorphism around the chromophore. Here, subatomic resolution X-ray structures of GFP without the structural polymorphism are reported. The positions of H atoms, hydrogen-bonding network patterns and accurate geometric parameters were determined for the two protonated forms. Compared with previously determined crystal structures and theoretically optimized structures, the anionic chromophores of the structures represent the authentic resonance state of GFP. In addition, charge-density analysis based on atoms-in-molecules theory and noncovalent interaction analysis highlight weak but substantial interactions between the chromophore and the protein environment. Considered with the derived chemical indicators, the lone pair–π interactions between the chromophore and Thr62 should play a sufficient role in maintaining the electronic state of the chromophore. These results not only reveal the fine structural features that are critical to understanding the properties of GFP, but also highlight the limitations of current quantum-chemical calculations.

Human telomeric G-quadruplexes have raised broad interest not just due to their involvement in the regulation of gene expressions and telomerase activities but also because of their application in nanoarchitectures. Herein, three azobenzene derivatives 1-3 were synthesized with different substituent groups and their photo-isomerization properties were investigated by UV/Vis spectroscopy. Then circular dichroism spectroscopy (CD), fluorescence experiments and native-gel electrophoresis were performed to evaluate their capabilities of conformational photo-regulation both in the absence and presence of metal ions. The results suggested that the compounds synthesized can successfully regulate the conformation of human telomeric G-quadruplex DNA in K(+) conditions to some extent. This work will initiate the possibility for the design and intriguing application of light-induced switching to photoregulate the conformation of G-quadruplex DNA under physiological conditions, providing a possible pathway to control G-quadruplex conformation in biological applications and also expanding the potential use of G-quadruplexes in nanomachines.

In the title solvate, C30H39NO5·CH4O {systematic name: 21-acet­oxy-18,21-dihy­droxy-5,6,16,18-tetra­methyl-10-phenyl-6,7-ep­oxy-[11]cytochalasa-13,19-dien-1-one methanol solvate}, the organic mol­ecule exhibits the tetra­cyclic terpenoid skeleton of cytochalasin, consisting of fused five-, six-, three- and 11-membered rings. The five-membered ring adopts an envelope conformation, while the six-membered ring is in a boat conformation. The ep­oxy O atom on the six-membered ring is pointing away from the five-membered ring. An inter­stitial methanol solvent mol­ecule is hydrogen bonded to the cytochalasin mol­ecules and inter­molecular O—H⋯O and N—H⋯O hydrogen bonds connect the mol­ecules into infinite chains along the (10) direction.

Correction for ‘Light-driven conformational regulation of human telomeric G-quadruplex DNA in physiological conditions’ by Xiwen Xing et al., Org. Biomol. Chem., 2011, 9, 6639–6645.

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