RESUMO
Hydrogen atoms are at the limit of visibility in X-ray structures even at high resolution. Neutron macromolecular crystallography (NMX) is an unambiguous method to locate hydrogens and study the significance of hydrogen bonding interactions in biological systems. Since NMX requires very large crystals, very few neutron structures of proteins have been determined yet. In addition, the most common hydrogen isotope 1H gives rise to significant background due to its large incoherent scattering cross-section. Therefore, it is advantageous to substitute as many hydrogens as possible with the heavier isotope 2H (deuterium) to reduce the sample volume requirement. While the solvent exchangeable hydrogens can be substituted by dissolving the protein in heavy water, complete deuterium labelling - perdeuteration - requires the protein to be expressed in heavy water with a deuterated carbon source. In this work, we developed an optimized method for large scale production of deuterium-labelled bacterial outer membrane protein F (OmpF) for NMX. OmpF was produced using deuterated media with different carbon sources. Mass spectrometry verified the integrity and level of deuteration of purified OmpF. Perdeuterated OmpF crystals diffracted X-rays to a resolution of 1.9 Å. This work lays the foundation for structural studies of membrane protein by neutron diffraction in future.
Assuntos
Deutério/química , Escherichia coli/genética , Difração de Nêutrons/métodos , Nêutrons , Porinas/química , Difração de Raios X/métodos , Clorófitas/química , Clorófitas/crescimento & desenvolvimento , Clonagem Molecular , Misturas Complexas/química , Cristalografia por Raios X/métodos , Meios de Cultura/química , Meios de Cultura/farmacologia , Escherichia coli/efeitos dos fármacos , Escherichia coli/metabolismo , Expressão Gênica , Vetores Genéticos/química , Vetores Genéticos/metabolismo , Modelos Moleculares , Porinas/genética , Porinas/isolamento & purificação , Porinas/metabolismo , Conformação Proteica em alfa-Hélice , Conformação Proteica em Folha beta , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismoRESUMO
Deuterium isotope labelling is important for structural biology methods such as neutron protein crystallography, nuclear magnetic resonance and small angle neutron scattering studies of proteins. Deuterium is a natural low abundance stable hydrogen isotope that in high concentrations negatively affect growth of cells. The generation time for Escherichia coli K-12 in deuterated medium is substantially increased compared to cells grown in hydrogenated (protiated) medium. By using a mutagenesis plasmid based approach we have isolated an E. coli strain derived from E. coli K-12 substrain MG1655 that show increased fitness in deuterium based growth media, without general adaptation to media components. By whole-genome sequencing we identified the genomic changes in the obtained strain and show that it can be used for recombinant production of perdeuterated proteins in amounts typically needed for structural biology studies.
