Video Experimental Relacionado
Updated: Jul 2, 2026
07:53
Analysis of Complex Molecules and Their Reactions on Surfaces by Means of Cluster-Induced Desorption/Ionization Mass Spectrometry
Published on: March 1, 2020
La ionización de residuos en LpxC observada directamente por la espectroscopia de RMN 67Zn
Andrew S Lipton1, Robert W Heck, Marcy Hernick
1Biological Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
Journal of the American Chemical Society
|September 3, 2008
Resumen
El pH afecta a la estructura de Aquifex aeolicus LpxC, como se muestra en (67) Zn NMR. Una mutación en His265 elimina esta dependencia del pH, lo que indica que His265
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Biología Estructural Biología estructural.
- La biofísica es la biofísica.
Sus antecedentes:
- Aquifex aeolicus LpxC es una enzima involucrada en la biosíntesis de lipopolisacáridos.
- Comprender el comportamiento dependiente del pH de LpxC es crucial para dilucidar su mecanismo catalítico.
- El sitio activo de la enzima contiene un ion de zinc esencial para su función.
Objetivo del estudio:
- Para investigar la dependencia del pH del estado sólido (67) Zn de las líneas de RMN de tipo salvaje (WT) y el mutante H265A Aquifex aeolicus LpxC.
- Para identificar los residuos del sitio activo cuyos estados de ionización cambian con el pH.
- Para correlacionar los hallazgos de RMN con la actividad enzimática y modelos computacionales.
Principales métodos:
- Espectroscopia de resonancia magnética nuclear (RMN) de estado sólido (67) Zn.
- Modelado mecánico cuántico / mecánico molecular (QM / MM).
- La cinética de las enzimas (implicada por los valores de pKa).
Principales resultados:
- WT LpxC exhibe espectros de RMN 67Zn dependientes del pH con especies distintas que aparecen en diferentes valores de pH, lo que corresponde a dos valores de pKa.
- El modelado QM/MM sugiere que los estados de ionización de Glu78 y His265 cambian con el pH.
- El mutante H265A muestra espectros independientes del pH, con Glu78 restante protonado y agua unida al ion zinc.
Conclusiones:
- La dependencia del pH de WT LpxC se atribuye a la ionización de los residuos del sitio activo, probablemente Glu78 y His265.
- His265 juega un papel importante en los cambios estructurales dependientes del pH de la enzima.
- El agua permanece coordinada con el ion zinc a través del rango de pH estudiado tanto en WT como en enzimas mutantes.
Más Videos Relacionados
Videos de Conceptos Relacionados
01:13¹H NMR: Complex Splitting
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
01:21Chemical Ionization (CI) Mass Spectrometry
The molecular ion peak of a molecule in the mass spectrum provides vital information for molecular identification. However, conventional electron impact ionization can lead to the rapid dissociation of some molecular ions before they reach the detector. A milder ionization method is required to increase the lifetime of such ionized analyte molecules. Chemical ionization (CI) is a gas-phase protonation reaction useful for mass-analyzing analyte molecules that are easily protonated to yield the...
01:10Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule
In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1 triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
01:24Mass Spectrum: Interpretation
An unknown compound can be established by identifying the molecular ion peak in the mass spectrum. The molecular ion peak is often weak or absent due to the predominance of fragmentation in high-energy electron beams. In such cases, a soft-energy electron beam can be used to scan the spectrum to enhance the intensity of the molecular ion peak. Additionally, chemical ionization, field ionization, and desorption ionization spectra are used to obtain a relatively intense molecular ion peak.To...
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
01:15Mass Spectrometry of Amines
In mass spectroscopy, amines undergo fragmentation to give parent ions with odd molecule weights. This observed mass spectrum follows the nitrogen rule; a molecule with an odd number of nitrogen atoms produces a molecular ion with an odd molecular weight. Amines undergo fragmentation through α cleavage, producing nitrogen-containing cations—iminium ions—and alkyl radicals. Mass spectra of aromatic and cyclic aliphatic amines exhibit strong molecular ion peaks, but acyclic aliphatic amines show...