2 research outputs found
Crystal Structure and Biochemical Characterization of an Aminopeptidase LapB from <i>Legionella pneumophila</i>
Aminopeptidases are a group of exopeptidases
that catalyze the
removal of a wide range of N-terminal amino acid residues from peptides
and proteins. They have many important commercial applications in
the food industry. We determined the crystal structure of an aminopeptidase
LapB from <i>Legionella pneumophila</i>. The overall structure
reveals that the N-terminal protease-associated (PA) domain presents
a new fold and shields the active site cavity of the conserved C-terminal
peptidase domain. The steady-state kinetic analysis of LapB and the
PA domain deletion mutant indicate that the PA domain inhibited enzyme
activity of the peptidase domain. Interestingly, the activity of LapB
was largely increased by various organic solvents such as ethanol,
propanol, and methanol at the concentration of 60% (v/v). CD analysis
provided evidence that organic solvents induce the PA domain conformational
changes that eliminate the inhibition role. The unique properties
indicate the application potential of LapB in the food processing
industry
Table_1_Simultaneous determination of nine phenolic compounds in imitation wild Dendrobium officinale samples using ultrahigh-performance liquid chromatography–tandem mass spectrometry.docx
Dendrobium officinale Kimura et Migo (D. officinale), one of the nine everlasting types of grass, has gained increasing attention owing to its important roles in alternative medicines and drug discovery. Due to its natural resources being in danger of being extinct, imitation wild planting is becoming increasingly common. To assess the product’s quality completely, an efficient ultrahigh performance liquid chromatography-triple quadrupole tandem mass spectrometry (UHPLC-QQQ-MS/MS) method was established to simultaneously quantify nine phenolic compounds in D. officinale samples. The extraction parameters, including solvent, solvent concentration, solid–liquid ratio, and extraction time, were systematically optimized with the single-factor test. The results demonstrated that extraction with a 1:200 solid-to-liquid ratio of 80% methanol for 1.5 h was the most efficient condition for the extraction of flavonoids. Satisfactory retention times and resolution of the nine analytes were acquired on the Thermo Scientific Hypersil GOLD column with multiple reaction monitoring in negative ion scanning mode. The method was validated to demonstrate its selectivity, linearity, precision, accuracy, and robustness. Thus, the verified UHPLC-QQQ-MS/MS method was successfully applied to the quantification of phenolic components present in D. officinale samples. The results indicated that the quantity and composition of phenolic components in D. officinale from various provenances were significantly different. This work provides a theoretical foundation for the cultivation and assessment of wild D. officinale quality.</p