63 research outputs found
Histidine Hydrogen-Deuterium Exchange Mass Spectrometry for Probing the Microenvironment of Histidine Residues in Dihydrofolate Reductase
Histidine Hydrogen-Deuterium Exchange Mass Spectrometry (His-HDX-MS) determines the HDX rates at the imidazole C(2)-hydrogen of histidine residues. This method provides not only the HDX rates but also the pK(a) values of histidine imidazole rings. His-HDX-MS was used to probe the microenvironment of histidine residues of E. coli dihydrofolate reductase (DHFR), an enzyme proposed to undergo multiple conformational changes during catalysis.Using His-HDX-MS, the pK(a) values and the half-lives (t(1/2)) of HDX reactions of five histidine residues of apo-DHFR, DHFR in complex with methotrexate (DHFR-MTX), DHFR in complex with MTX and NADPH (DHFR-MTX-NADPH), and DHFR in complex with folate and NADP+ (DHFR-folate-NADP+) were determined. The results showed that the two parameters (pK(a) and t(1/2)) are sensitive to the changes of the microenvironment around the histidine residues. Although four of the five histidine residues are located far from the active site, ligand binding affected their pK(a), t(1/2) or both. This is consistent with previous observations of ligand binding-induced distal conformational changes on DHFR. Most of the observed pK(a) and t(1/2) changes could be rationalized using the X-ray structures of apo-DHFR, DHFR-MTX-NADPH, and DHFR-folate-NADP+. The availability of the neutron diffraction structure of DHFR-MTX enabled us to compare the protonation states of histidine imidazole rings.Our results demonstrate the usefulness of His-HDX-MS in probing the microenvironments of histidine residues within proteins
Reaction of 3,4-Diaminopyridazine with Ξ±,Ξ²-Dicarbonyl compounds, carbon disulfide and urea, and methylation of some of the products
Purine analogues as amplifiers of phleomycin. VIII. Some Thiazolo[4,5-b]pyrazines and related compounds
Purine analogues as amplifiers of phleomycin. VII. Some 1H-imidazo-[4,5-b]pyrazines and related compounds
Imidazo[1,2-B]Pyridazines. I. Some 3-Alkoxy-6-Halogeno-2-Phenyl-(and 4β²-Substituted Phenyl)Imidazo[1,2-B]Pyridazines and 3-Methoxy-2,6-Diphenylimidazo[1,2-B]Pyridazine
Heterocyclic amplifiers of phleomycin. II. Thiazol-4'-ylpyrazines with phenyl substituents and strongly basic side chains
Heterocyclic amplifiers of phleomycin. III. 5-Substituted 1 H-Imidazo[4,5-b]pyrazines and 6-substituted Pyrazino[2,3-b]pyrazines
Potential antimalarials. II. N4-Substituted 2-Methoxy(and 2-hydroxy)-1,5-naphthyridin-4-amines
Potential Antimalarials. IX. Di-mannich Bases of 4-(7β²-trifluoro-methylquinazolin-4β²-ylamino)phenol and 4-(7β²-Trifluoromethylquinolin-4β²-ylamino)phenol
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