RESUMEN
The secretory granule of the pancreatic ß-cells is a zinc-rich environment copopulated with the hormones amylin and insulin. The human amylin is shown to interact with zinc ions with major contribution from the single histidine residue, which is absent in amylin from other species such as cat, rhesus and rodents. We report here the interaction of murine amylin with zinc ions in vitro. The self-assembly of murine amylin is tightly regulated by zinc and pH. Ion mobility mass spectrometry revealed zinc interaction with monomers and oligomers. Nuclear magnetic resonance confirms the binding of zinc to murine amylin. The aggregation process of murine amylin into amyloid fibrils is accelerated by zinc. Collectively these data suggest a general role of zinc in the modulation of amylin variants oligomerization and amyloid fibril formation.
Asunto(s)
Polipéptido Amiloide de los Islotes Pancreáticos/química , Zinc/farmacología , Amiloide/biosíntesis , Amiloide/efectos de los fármacos , Animales , Concentración de Iones de Hidrógeno , Polipéptido Amiloide de los Islotes Pancreáticos/efectos de los fármacos , Espectroscopía de Resonancia Magnética , Espectrometría de Masas , Ratones , Agregado de Proteínas/efectos de los fármacosRESUMEN
RhlR is a 241-residue quorum sensing receptor that controls the expression of a myriad of virulence genes in Pseudomonas aeruginosa. Here, the DNA sequence encoding the carboxi-terminal DNA-binding domain of RhlR was cloned into the pET-RP1B plasmid and expressed as an N-terminal fusion protein to the expression/purification Thio6His6 tag. The fusion construct expressed insolubly in Escherichia coli BL21 (DE3) cells. The recombinant protein was extracted from the bacterial inclusion bodies and refolded in the presence of the charged amino acids l-arginine and l-glutamate. The refolded protein was purified by a combination of Ni(+2)-affinity and size exclusion chromatography, allowing the production of 2 mg of highly purified protein (>95% purity) per 5 mg of wet cells derived from 1 L culture. (1)H 1D NMR analysis revealed that the recombinant protein is folded. Moreover, a fluorescence anisotropy DNA-binding assay showed that the refolded protein is functional, as it recognizes the rhlAB promoter. This is the first time that a domain of the quorum sensing regulator RhlR was produced in sufficient amounts for structural studies, enabling the investigation of the molecular basis for RhlR specific interaction with DNA promoters.
Asunto(s)
Proteínas Bacterianas/química , Proteínas de Unión al ADN/química , Percepción de Quorum/genética , Proteínas Bacterianas/genética , Proteínas Bacterianas/aislamiento & purificación , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/aislamiento & purificación , Escherichia coli/genética , Regulación Bacteriana de la Expresión Génica , Regiones Promotoras Genéticas , Pliegue de Proteína , Pseudomonas aeruginosa/genéticaRESUMEN
The prion protein (PrP) is the major agent involved in the transmissible spongiform encephalopathies (TSEs). Nucleic acids have been reported to bind PrP with high affinity, although the physiopathological roles for recognition are still not clear. In this work we investigate the stability of a soluble, 1:1 complex formed between an 18 base-pair DNA fragment and the full-length murine recombinant prion protein (mrPrP). DNA confers a gain in mrPrP stability against urea and guanidinium denaturation, which is enhanced at lower pHs and in moderate concentrations of NaCl. We discuss the cooperative folding transition coupled to DNA binding and acidification in terms of the possible cellular scenarios found during complex internalization and degradation.
Asunto(s)
ADN/química , Priones/química , Animales , Fluorescencia , Guanidina , Concentración de Iones de Hidrógeno , Ratones , Desnaturalización Proteica , Pliegue de Proteína , Estabilidad Proteica , Proteínas Recombinantes/química , Sales (Química) , Análisis Espectral , UreaRESUMEN
The infectious agent of transmissible spongiform encephalopathies (TSE) is believed to comprise, at least in part, the prion protein (PrP). Other molecules can modulate the conversion of the normal PrP(C) into the pathological conformer (PrP(Sc)), but the identity and mechanisms of action of the key physiological factors remain unclear. PrP can bind to nucleic acids with relatively high affinity. Here, we report small-angle X-ray scattering (SAXS) and nuclear magnetic resonance spectroscopy measurements of the tight complex of PrP with an 18 bp DNA sequence. This double-stranded DNA sequence (E2DBS) binds with nanomolar affinity to the full-length recombinant mouse PrP. The SAXS data show that formation of the rPrP-DNA complex leads to larger values of the maximum dimension and radius of gyration. In addition, the SAXS studies reveal that the globular domain of PrP participates importantly in the formation of the complex. The changes in NMR HSQC spectra were clustered in two major regions: one in the disordered portion of the PrP and the other in the globular domain. Although interaction is mediated mainly through the PrP globular domain, the unstructured region is also recruited to the complex. This visualization of the complex provides insight into how oligonucleotides bind to PrP and opens new avenues to the design of compounds against prion diseases.
