Suchergebnisse

The isoelectric point (pI) of a protein is a key characteristic that influences its overall electrostatic behaviour. The majority of conventional methods for the determination of the isoelectric point of a molecule rely on the use of spatial gradients in pH, although significant practical challenges are associated with such techniques, notably the difficulty in generating a stable and well controlled pH gradient. Here, we introduce a gradient-free approach, exploiting a microfluidic platform which allows us to perform rapid pH change on chip and probe the electrophoretic mobility of species in a controlled field. In particular, in this approach, the pH of the electrolyte solution is modulated in time rather than in space, as in the case for conventional determinations of the isoelectric point. To demonstrate the general approachability of this platform, we have measured the isoelectric points of representative set of seven proteins, bovine serum albumin, $\beta$-lactoglobulin, ribonuclease A, ovalbumin, human transferrin, ubiquitin and myoglobin in microlitre sample volumes. The ability to conduct measurements in free solution thus provides the basis for the rapid determination of isoelectric points of proteins under a wide variety of solution conditions and in small volumes. ; We acknowledge financial support from the Biotechnology and Biological Sciences Research Council, the Newman Foundation and the Elan Pharmaceuticals. The research leading to these results has also received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007- 2013) through the ERC grant PhysProt (agreement n1 337969).

The conversion of human lysozyme into amyloid fibrils is associated with a rare but fatal hereditary form of nonneuropathic systemic amyloidosis. The accumulation of large amounts of aggregated protein is thought to be initiated by the formation of transient intermediate species of disease-related lysozyme variants, essentially due to the loss of global cooperativity under physiologically relevant conditions. Interestingly, all five naturally occurring, amyloidogenic, single-point mutations are located in the β-domain of lysozyme, the region that is predominantly unfolded during the formation of the transient intermediate species. Given the lack of known naturally occurring, amyloidogenic, single-point mutations in the α-domain, we chose three specific mutations to address the effects that location may have on native-state dynamics, as studied by hydrogen-deuterium (HD) exchange experiments analyzed by NMR spectroscopy, and mass spectrometry. We compared the effect of a destabilizing α-domain mutation (I23A) with that of the well-characterized I59T β-domain variant. We also investigated the effect of a mutation that has minor effects on native-state stability at the domain interface (I56V) and compared it with that of a variant with similar stability within the C-helix (I89V). We show that when variants have similar reduced native-state stabilities, the location of the mutation (I23A versus I59T) is crucial to the native-state dynamics, with the α-domain mutation having a significantly lower ability to populate transient intermediate species under physiologically relevant conditions. Interestingly, the mutation at the interface (I56V) has a greater effect in facilitating the formation of transient intermediate species at elevated temperatures compared with the variants containing α-domain mutations, even though this mutation results in only minor changes to the native-state stability of lysozyme. These findings reveal that the location of specific mutations is an important factor in determining the native-state dynamical properties of human lysozyme in the context of its propensity to populate the aggregation-prone transient intermediate species associated with pathogenic amyloid formation. ; This research was supported by the Biotechnology and Biological Sciences Research Council (BB/E019927/1 to C.M.D., C.V.R., and J.R.K.), the Medical Research Council (E.D.G. and C.M.D.), the Belgian Program of Interuniversity Attraction Poles administered by the Federal Office for Scientific Technical and Cultural Affairs (PAI numbers P6/19 and P7144 to C.M.D. and M.D.), the European Union's Sixth Framework Program (LSHM-CT-2006-037525 to C.M.D. and M.D.), and Programme grants from the Wellcome Trust and the Leverhulme Trust (C.M.D.). It was also supported by a Korean Government Scholarship for Overseas Studies (M.A.), the Winston Churchill Foundation (C.L.H.), and Boerhinger Ingleheim funds (A.D.). The NMR facility at the Department of Chemistry, University of Cambridge, is supported in part by an EPSRC Core Capability grant (EP/K039520/1).