Ngan Nguyen Bich

Green-to-red photoconvertible Dronpa mutant for multimodal super-resolution fluorescence microscopy

Advanced imaging techniques crucially depend on the labels used. In this work, we present the structure-guided design of a fluorescent protein that displays both reversibly photochromic and green-to-red photoconversion behavior. We first designed ffDronpa, a mutant of the photochromic fluorescent protein Dronpa that matures up to three times faster while retaining its interesting photochromic features. Using a combined evolutionary and structure-driven rational design strategy, we developed a green-to-red photoconvertible ffDronpa mutant, called pcDronpa, and explored different optimization strategies that resulted in its improved version, pcDronpa2. This fluorescent probe combines a high brightness with low photobleaching and photoblinking. We herein show that, despite its tetrameric nature, pcDronpa2 allows for multimodal subdiffraction imaging by sequentially imaging a given sample using both super-resolution fluctuation imaging and localization microscopy.

Structural basis for the influence of a single mutation K145N on the oligomerization and photoswitching rate of Dronpa.

The crystal structure of the on-state of PDM1-4, a single-mutation variant of the photochromic fluorescent protein Dronpa, is reported at 1.95 Å resolution. PDM1-4 is a Dronpa variant that possesses a slower off-switching rate than Dronpa and thus can effectively increase the image resolution in subdiffraction optical microscopy, although the precise molecular basis for this change has not been elucidated. This work shows that the Lys145Asn mutation in PDM1-4 stabilizes the interface available for dimerization, facilitating oligomerization of the protein. No significant changes were observed in the chromophore environment of PDM1-4 compared with Dronpa, and the ensemble absorption and emission properties of PDM1-4 were highly similar to those of Dronpa. It is proposed that the slower off-switching rate in PDM1-4 is caused by a decrease in the potential flexibility of certain β-strands caused by oligomerization along the AC interface.

Stacking patterns of thieno[3,2-b]thiophenes functionalized by sequential palladium-catalyzed Suzuki and Heck cross-coupling reactions.

The crystal structures of three 5-alkenyl-2-arylthieno[3,2-b]thiophenes, namely 3,6-dibromo-5-(4-tert-butylstyryl)-2-(naphthalen-1-yl)thieno[3,2-b]thiophene, C(28)H(22)Br(2)S(2), (I), 3,6-dibromo-5-(4-methylstyryl)-2-(naphthalen-1-yl)thieno[3,2-b]thiophene, C(25)H(16)Br(2)S(2), (II), and 3,6-dibromo-2-(4-tert-butylphenyl)-5-(4-methylstyryl)thieno[3,2-b]thiophene, C(25)H(22)Br(2)S(2), (III), have been determined in order to evaluate the geometry of the molecules. The π-conjugated system containing the thieno[3,2-b]thiophene skeleton, the ethylene bridge and the phenyl rings is almost planar. The aromatic ring directly attached to the thieno[3,2-b]thiophene moiety is not coplanar with the thieno[3,2-b]thiophene moiety itself due to steric hindrance of the bromo substituent. The crystal packings are characterized by π-π stacking [only for (II)] and C-Br...π interactions. The long axes of the molecules in (I) are oriented in two directions; for the two other structures the long axis is oriented in one direction only.

Crystal structures of organoplatinum complexes containing alkyl­eugenoxyacetate and p-chloro­aniline

In the title trans-dichloridoplatinum(II) complexes, the central PtII atom is further coordinated by the p-chloroaniline N atom and ethylenic double bond of alkyleugenoxyacetate.

Crystal structure of hexa­aqua­nickel(II) bis{2-[(5,6-di­hy­droxy-3-sul­fon­ato­quino­lin-1-ium-7-yl)oxy]acetate} dihydrate

In the packing of the title compound, Ni(H2O)6 is acting as a glue between neighbouring zwitterionic quinoline derivatives which are not directly complexing with NiII.

Crystal structures of three 4-substituted-2,2'-bipyridines synthesized by Sonogashira and Suzuki-Miyaura cross-coupling reactions

In the crystal structures of three 4-substituted-2,2′-bipyridines prepared using facile synthetic procedures, two novel 4-alkynyl-2,2-bipyridines via the Sonogashira cross-coupling reaction and one 4-aryl-2,2′-bipyridine via the Suzuki–Miyaura cross-coupling reaction, the planar 4-alkynyl-substituted derivatives are in contrast to the non-planar 4-aryl derivative.

Crystal structure of trans-di­chlorido­(4-nitro­aniline-κN1)(piperidine-κN)platinum(II)

The packing of the title compound features N—H⋯Cl hydrogen bonds and π–π stacking interactions, which form one-dimensional chains of molecules parallel to [001] further linked via N—H⋯O interactions.

Crystal structure of chlorido­(piperidine-κN)(quinoline-2-carboxyl­ato-κ2N,O)platinum(II)

The platinum(II) complex with notable antitumor activity shows a slightly distorted square-planar coordination and intramolecular C—H⋯Cl and intermolecular N—H⋯Cl and C—H⋯O hydrogen bonds.

Structures of states of a photoconvertible and photoswitchable fluorescent protein engineered from Dronpa

The structures of several states of a new photoconvertible and photoswitchable fluorescent protein (FP) engineered from Dronpa [1], called pcDronpa (photoconvertible Dronpa), were determined. Like IrisFP [2] and NijiFP [3], pcDronpa possesses both photoconvertible and photoswitching properties. However, pcDronpa shows the success of introducing photoconvertibility into the photoswichable FP. The green fluorescent state (green-on state) of pcDronpa can switch reversibly to the nonfluorescent state (green-off state) by illumination with 488-nm and 405-nm light, respectively. The structural basis for this switching was proven by the crystal structure determination of the green-on and green-off states. The photoswitching of pcDronpa is as expected not different from that of Dronpa [4], because there is no alternation in the part of the chromophore responsible for the photoswitching, as well as in its proximate environment. Remarkably, pcDronpa can also convert to the red fluorescent state (red-on state) by illumination with 405-nm light. This property was introduced by rationally mutating the chromophore from Cys-Tyr-Gly to His-Tyr-Gly.