Identification and Characterization of a B-Raf Kinase α-Helix Critical for the Activity of MEK Kinase in MAPK Signaling

In the MAPK pathway, an oncogenic V600E mutation in B-Raf kinase causes the enzyme to be constitutively active, leading to aberrantly high phosphorylation levels of its downstream effectors, MEK and ERK kinases. The V600E mutation in B-Raf accounts for more than half of all melanomas and ∼3% of all cancers, and many drugs target the ATP binding site of the enzyme for its inhibition. Because B-Raf can develop resistance against these drugs and such drugs can induce paradoxical activation, drugs that target allosteric sites are needed. To identify other potential drug targets, we generated and kinetically characterized an active form of B-Raf^V600E expressed using a bacterial expression system. In doing so, we identified an α-helix on B-Raf, found at the B-Raf-MEK interface, that is critical for their interaction and the oncogenic activity of B-Raf^V600E. We assessed the binding between B-Raf mutants and MEK using pull downs and biolayer interferometry and assessed phosphorylation levels of MEK in vitro and in cells as well as its downstream target ERK to show that mutating certain residues on this α-helix is detrimental to binding and downstream activity. Our results suggest that this B-Raf α-helix binding site on MEK could be a site to target for drug development to treat B-Raf^V600E-induced melanomas.

[The relationship between bile acid and factors relative to gastric cancer]

By high performance liquid chromatography and 3a-hydroxysteroid dehydrogenase determination, we quantitatively analysed the content of 8 combined biliary acid salt and pH of gastric juice from 35 patients with gastric disease and healthy controls. It was found that both the content of various kinds of biliary acid salt and pH value of gastric juice were much higher in patients with gastric cancer, gastric ulcer, and chronic atrophic gastritis than in normal controls, bile acid salt is known to be harmful to gastric mucosa and that the damage becomes more severe with the increase of bile acid salt concentration and prolongation of exposure, therefore our results suggest that the bile acid salt in the gastric juice is one of the carcinogenic factors.

High-performance liquid chromatographic separation of racemic and diastereomeric mixtures of 2,4-pentadienoate-iron tricarbonyl derivatives

beta-Cyclodextrin chiral stationary phase facilitates the chiral separation of the (+/-)-methyl-5-formyl-2,4-pentadienoate-iron tricarbonyl (1) racemic mixture. The separation of oxazolidine derivatives 2 and 3 diastereomers were achieved with a C18 column but the compounds underwent in-column hydrolysis to give (-)- and (+)-1, respectively. This hydrolysis was exploited for the determination of 2 and 3 by the beta-cyclodextrin column, namely 2 and 3 were initially and completely hydrolyzed in the column to give (-)- and (+)-1 and this racemic mixture was then separated by this chiral column.

Thermal lens-circular dichroism detector for high-performance liquid chromatography

A novel and ultrasensitive chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents by the thermal lens effect. In this instrument, the chromatographic effluent was sequentially excited by left circularly polarized laser light (LCPL) and right circularly polarized laser light (RCPL); both of these excitation beams were derived from the same argon ion laser whose linearly polarized output was transformed into circularly polarized light by means of a Pockels cell. The heat generated as a consequence of the sample absorption of the LCPL and RCPL was measured by the probe laser beam collinearly overlapping with the two excitation beams. A lock-in amplifier was used to measure the thermal lens-circular dichroism (TL-CD) signal which corresponds to the difference in the thermal lens signals produced by the LCPL and RCPL excitation beams. In addition to its high sensitivity, the advantages of this TL-CD chiral detector include its ability to provide, directly and in real time, information on the chirality (i.e., circular dichroism) and optical purity of chiral samples. A detection limit of 7.2 ng was achieved for (-)-tris(ethylenediamine)cobalt(III) (k' = 0.45) as well as for the (+)-tris(ethylenediamine)cobalt(III) (k' = 1.40) when these two enantiomers were chromatographically separated from the corresponding racemic mixture through the use of bis(mu-d-tartrato)diantiomonate(III) ion pair reversed-phase chromatography. This limit of detection was found by using a 10-microL flow cell and having 5-mm path length and 6-mW excitation laser beam (lambda = 514.5 nm) modulated at 2 Hz.