RESUMEN
Secondary ion mass spectrometry (SIMS) applied in the event-by-event bombardment/detection mode is uniquely suited for the characterization of individual nano-objects. In this approach, nano-objects are examined one-by-one, allowing for the detection of variations in composition. The validity of the analysis depends upon the ability to physically isolate the nano-objects on a chemically inert support. This requirement can be realized by deposition of the nano-objects on a Nano-Assisted Laser Desorption/Ionization (NALDI™) plate. The featured nanostructured surface provides a support where nano-objects can be isolated if the deposition is performed at a proper concentration. We demonstrate the characterization of individual nano-objects on a NALDI™ plate for two different types of nanometric bacteriophages: Qß and M13. Scanning electron microscope (SEM) images verified that the integrity of the phages is preserved on the NALDI™ substrate. Mass spectrometric data show secondary ions from the phages are identified and resolved from those from the underlying substrate.
RESUMEN
Human retinol-binding protein (RBP) is a monomeric 21-kDa protein that is currently the subject of numerous studies owing to its role in the cellular uptake and utilization of retinol. When the RBP gene is overexpressed in Escherichia coli, inclusion bodies of aggregated RBP are found in the cells. These inclusion bodies are solubilized in 5.0 M GdmCl containing 10 mM DTT. Refolding of RBP is carried out in the presence of vitamin A by diluting denatured and reduced RBP into a redox refolding buffer consisting of 3 mM cysteine/0.3 mM cystine at 4 degreesC. Ion exchange chromatography (HPLC) is utilized to purify refolded RBP to homogeneity as demonstrated by SDS-PAGE and electrospray MS. The native structure of refolded RBP was established by its ability to bind to vitamin A and the plasma protein transthyretin. The reconstitution of RBP outlined within affords a 50-60% overall yield, i.e., 73 mg of pure RBP/L of E. coli culture.
Asunto(s)
Proteínas de Unión al Retinol/química , Cromatografía por Intercambio Iónico , Disulfuros/química , Escherichia coli/genética , Expresión Génica , Humanos , Técnicas In Vitro , Cuerpos de Inclusión/química , Pliegue de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Proteínas de Unión al Retinol/genética , Proteínas de Unión al Retinol/metabolismo , Proteínas Plasmáticas de Unión al Retinol , Solubilidad , Vitamina A/metabolismoRESUMEN
Modification of arginine residues in bradykinin, [1-5]-bradykinin, splenopentin and two synthetic pentapeptides with acetylacetone (pentane-2,4-dione) significantly increases the relative abundance of sequence-specific fragment ions produced by matrix-assisted laser desorption/ionization (MALDI). The fragmentation efficiency as measured by post-source decay in a reflectron time-of-flight mass spectrometer increases by a factor of 2-3.5. Peptide bonds adjacent to modified residues are more susceptible to cleavage than in the non-derivatized peptide ions. The increased lability of these bonds gives rise to more complete sequence information. In addition, the relative abundances of sequence-specific fragment ions are enhanced. This strategy makes it possible to obtain valuable structural information from arginine-containing peptides that otherwise do not fragment well.
