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...
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...
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