@article {YANG2019,
	title = {Evaluation of the Binding of Natural Products with Thrombin Binding Aptamer G-Quadruplex Using Electrospray Ionization Mass Spectrometry and Spectroscopic Methods},
	journal = {Talanta},
	volume = {200},
	year = {2019},
	month = {08/2019},
	pages = {424-431},
	abstract = {<p>A 15-mer thrombin-binding aptamer (TBA) was discovered with specificity for thrombin. It forms a unique G-quadruplex (G4), which is postulated to be the molecular basis for its binding specificity. Many analytical methods make use of affinity binding between the thrombin and TBA as they form a very stable complex. We develope a strategy to stabilize TBA/G4\&$\#$39;s structure by introducing G4-interactive molecules, which may enhance its ability to recognize the target. Herein, a fast screening ESI-MS assay was employed to determine potential binding of natural products molecules with the TBA/G4 complex. The experimental results showed that four investigated natural alkaloids had apparent binding affinities. One of them, jatrorrhizine (L1), has been shown to bind strongly to the TBA/G4 mainly in 1:2 M ratio. Once the working conditions were established, the interaction of the jatrorrhizine with the TBA/G4 was explored using a combination of ESI-MS and spectroscopic techniques. Ligand-induced effects on TBA/G4 structure and its stability were examined by means of circular dichroism (CD). Jatrorrhizine inducing the G4 formation seems also to be the more effective in terms of thermal stabilization under the experimental conditions used. Both results of UV and fluorescence experiments undoubtedly showed a good binding affinity with the binding constant around 105L\&bull;mol\&minus;1. The stacking interactions of jatrorrhizine with the G-tetrads in TBA/G4 were further confirmed by competition experiment. ESI-MS was carried out to determine the coexistence of 1:1 and 1:2 complexes in TBA/G4-L1 system, and showed a dynamical shift from 1:1 to 1:2 complex in minutes.</p>},
	keywords = {Electrospray ionization mass spectrometry, fluorescence spectroscopy, jatrorrhizine, noncovalent interaction, Thrombin binding aptamer},
	issn = {0039-9140},
	doi = {https://doi.org/10.1016/j.talanta.2019.03.080},
	url = {http://www.sciencedirect.com/science/article/pii/S0039914019303376},
	author = {Pengfei Yang and Xinyi Wang and Zhenggui Gu and Huihui Li and David D.Y. Chen and Xiaodi Yang}
}
@article {3621,
	title = {Probing the role of tryptophan residues in a cellulose-binding domain by chemical modification},
	journal = {Protein Science},
	volume = {5},
	number = {11},
	year = {1996},
	note = {ISI Document Delivery No.: VQ786Times Cited: 41Cited Reference Count: 34},
	month = {Nov},
	pages = {2311-2318},
	type = {Article},
	abstract = {The cellulose-binding domain (CBDCex) of the mixed function glucanase-xylanase Cex from Cellulomonas fimi contains five tryptophans, two of which are located within the p-barrel structure and three exposed on the surface (Xu GY et al., 1995, Biochemistry 34:6993-7009). Although all five tryptophans can be oxidized by N-bromosuccinimide (NBS), stopped-flow measurements show that three tryptophans react faster than the other two. NMR analysis during the titration of CBDCex with NBS shows that the tryptophans on the surface of the protein are fully oxidized before there is significant reaction with the two buried tryptophans. Additionally, modification of the exposed tryptophans does not affect the conformation of the backbone of CBDCex, whereas complete oxidation of all five tryptophans denatures the polypeptide. The modification of the equivalent of one and two tryptophans by NBS reduces binding of CBDCex to cellulose by 70\% and 90\%, respectively. This confirms the direct role of the exposed aromatic residues in the binding of CBDCex to cellulose. Although adsorption to cellulose does afford some protection against NBS, as evidenced by the increased quantity of NBS required to oxidize all of the tryptophan residues, the polypeptide can still be oxidized completely when adsorbed. This suggests that, whereas the binding appears to be irreversible overall [Ong E et al., 1989, Bio/Technology 7:604-607], each of the exposed tryptophans interacts reversibly with cellulose.},
	keywords = {absorbance spectroscopy, ACTIVE-SITE, CELLOBIOHYDROLASE-I, cellulose-binding, ENDOGLUCANASE, ESCHERICHIA-COLI, FIMI, fluorescence spectroscopy, N-bromosuccinimide, NMR, NUCLEAR-MAGNETIC-RESONANCE, SCHIZOPHYLLUM-COMMUNE, SPECTROSCOPY, TRICHODERMA-REESEI, XYLANASE-A},
	isbn = {0961-8368},
	url = {<Go to ISI>://A1996VQ78600017},
	author = {Bray, M. R. and Johnson, P. E. and Gilkes, N. R. and McIntosh, L. P. and Kilburn, D. G. and Warren, R. A. J.}
}
