No abstract

Associations between PPI use, encephalopathy and higher MELD scores imply caution should be exercised in prescribing gastric acid suppressants to patients with cirrhosis, particularly in the absence of clear indications.

Self-assembly of peptides and proteins into the ordered fibrillar aggregates known as amyloid fibrils has potential for achieving control over molecular-level architecture and macroscopic properties. Polypeptide fibrils have been suggested as templates for ordering inorganic components in nanoassemblies, [1] or as the basis for biomaterials. [2][3][4] The ordered self-assembly of proteins and polypeptides is also of interest in the context of the protein misfolding disorders, including Alzheimers disease and type 2 diabetes. The vast majority of systems that form amyloid-like fibrils assemble by a nucleation and growth mechanism [5] whereby the formation of a multimeric nucleus of polypeptide molecules drives selfassembly. The considerable experimental difficulties associated with observing a small and potentially rare aggregate or aggregates in a soup of molecules have impeded characterization of these triggers to growth.Herein we probe by time-course mass spectrometry (MS) and ion-mobility mass spectrometry (IM-MS) the early aggregation states of an amyloidogenic endecapeptide (sequence YTIAALLSPYS) derived from amino acid residues 105-115 of the human plasma protein transthyretin (TTR 105-115). The mobility K of an ion (and its corresponding reduced mobility K 0 ) is obtained from the arrivaltime distribution (ATD) of a given ion after it has passed through a drift cell filled with a buffer gas under the influence of a weak electric field. K is inversely related to the orientationally averaged collision cross-section W by a modified version of Equation (1):where z is ion charge, e is electron charge, N 0 the buffer gas number density, m the reduced mass of the buffer gas and ion, k B the Boltzmann constant, T the effective temperature, and W is the momentum transfer collision integral.The use of MS methods, and in particular IM-MS, can provide molecular detail on the early stages of aggregation of amyloidogenic peptides and proteins. A large body of work assessing the configurations of species formed during polypeptide aggregation has utilized MS techniques: for example, Bowers and co-workers have examined the self-assembly of Ab, [6] a-synuclein, [7] IAPP, [8] and most recently a prion protein fragment.[9] The unique benefit of this approach is illustrated by a study of early aggregate species formed by the Alzheimers-related peptide Ab1-42 and the non-amyloidogenic variant Ab1-42 F19P (by Bernstein and co-workers [10] ). Resolved species in an ATD following nESI-MS of Ab1-42 were assigned to dimer, tetramer, hexamer, and dodecamer (n = 1, 2, 3, and 6 respectively) whereas the F19P mutant contained only dimer and tetramer. Furthermore, the absence of aggregates intermediate between putative hexamers and dodecamers led the authors to speculate that the hexamer was the building block of protofibril formation, a finding corroborated by cross-linking studies. [11][12][13] Recent work by Ashcroft and co-workers [14] describes the conformation of b2m oligomers up to the tetramer, finding compact dimers and elongate...

Wie man einen Knoten bindet: Die Verschmelzung von Katalyse und Koordinationschemie ermöglicht es zwei CuI‐Ionen (rot; siehe Bild), gemeinsam einen molekularen Dreifachknoten zu binden. Ein Ion verschlingt einen acyclischen Baustein und erzeugt so eine Schlaufe im Liganden, das andere schnappt sich die reaktiven Endgruppen des Liganden, fädelt sie durch die Schlaufe und katalysiert den kovalenten Einfang der Knotenarchitektur durch eine Alkin‐Azid‐Klickreaktion.

A prevalent type of protein misfolding causes the formation of β-sheet-rich structures known as amyloid fibrils. Research into the mechanisms of fibril formation has implications for both disease prevention and nanoscale templating technologies. This investigation into the aggregation of insulin utilises ion mobility mass spectrometry coupled with molecular modelling to identify and characterise oligomers formed during the 'lag' phase that precedes fibril growth. High resolution mass spectrometry and collision induced dissociation is used to unequivocally assign species as m/z coincident multimers or confomers, providing a robust analytical approach that supports the use of molecular dynamics to atomistically resolve the observed oligomers. We show that insulin oligomerises to form species In where 2 ≤ n ≤ 12 and within this set of oligomers we delineate over 60 distinct conformations, the most dominant of which are compact species. Modelling trained with experimental data suggests that the dominant compact dimers are enriched in β-sheet secondary structure and dominated by hydrophobic interactions, and provides a linear relationship between Rg and collision cross section. This approach provides detailed insight to the early stages of assembly of this much studied amyloidogenic protein, and can be used to inform models of nucleation and growth.

Self-assembly of peptides and proteins into the ordered fibrillar aggregates known as amyloid fibrils has potential for achieving control over molecular-level architecture and macroscopic properties. Polypeptide fibrils have been suggested as templates for ordering inorganic components in nanoassemblies, [1] or as the basis for biomaterials. [2][3][4] The ordered self-assembly of proteins and polypeptides is also of interest in the context of the protein misfolding disorders, including Alzheimers disease and type 2 diabetes. The vast majority of systems that form amyloid-like fibrils assemble by a nucleation and growth mechanism [5] whereby the formation of a multimeric nucleus of polypeptide molecules drives selfassembly. The considerable experimental difficulties associated with observing a small and potentially rare aggregate or aggregates in a soup of molecules have impeded characterization of these triggers to growth.Herein we probe by time-course mass spectrometry (MS) and ion-mobility mass spectrometry (IM-MS) the early aggregation states of an amyloidogenic endecapeptide (sequence YTIAALLSPYS) derived from amino acid residues 105-115 of the human plasma protein transthyretin (TTR 105-115). The mobility K of an ion (and its corresponding reduced mobility K 0 ) is obtained from the arrivaltime distribution (ATD) of a given ion after it has passed through a drift cell filled with a buffer gas under the influence of a weak electric field. K is inversely related to the orientationally averaged collision cross-section W by a modified version of Equation (1):where z is ion charge, e is electron charge, N 0 the buffer gas number density, m the reduced mass of the buffer gas and ion, k B the Boltzmann constant, T the effective temperature, and W is the momentum transfer collision integral.The use of MS methods, and in particular IM-MS, can provide molecular detail on the early stages of aggregation of amyloidogenic peptides and proteins. A large body of work assessing the configurations of species formed during polypeptide aggregation has utilized MS techniques: for example, Bowers and co-workers have examined the self-assembly of Ab, [6] a-synuclein, [7] IAPP, [8] and most recently a prion protein fragment.[9] The unique benefit of this approach is illustrated by a study of early aggregate species formed by the Alzheimers-related peptide Ab1-42 and the non-amyloidogenic variant Ab1-42 F19P (by Bernstein and co-workers [10] ). Resolved species in an ATD following nESI-MS of Ab1-42 were assigned to dimer, tetramer, hexamer, and dodecamer (n = 1, 2, 3, and 6 respectively) whereas the F19P mutant contained only dimer and tetramer. Furthermore, the absence of aggregates intermediate between putative hexamers and dodecamers led the authors to speculate that the hexamer was the building block of protofibril formation, a finding corroborated by cross-linking studies. [11][12][13] Recent work by Ashcroft and co-workers [14] describes the conformation of b2m oligomers up to the tetramer, finding compact dimers and elongate...

Die Hochzeit von Koordinationschemie und Katalyse ermöglicht es Metallionen, in Partnerschaft bei der Aktivtemplatsynthese des kleinsten bisher bekannten molekularen Dreifachknotens zusammenzuarbeiten. In ihrer Zuschrift auf beschreiben D. A. Leigh et al., wie ein CuI‐Ion innerhalb eines acyclischen Bausteins eine Schlaufe erzeugt, während ein zweites CuI‐Ion die reaktiven Endgruppen des Liganden koordiniert, die Schlaufe einfädelt und den aus 76 Atomen bestehenden Knoten durch eine Alkin‐Azid‐Klickreaktion fixiert.

The marriage … … of coordination chemistry and catalysis enables metal ions to work in partnership in the active-template synthesis of the smallest molecular trefoil knot reported to date. In their Communication on page 12 280 ff., D. A. Leigh et al. describe how one copper(I) ion entangles an acyclic building block to create a loop in the ligand whilst a second copper(I) ion gathers the ligand's reactive end groups, threads the loop, and catalyzes the covalent capture of the 76-atom knot by an alkyne-azide "click" reaction.