Article

The kinetics of aggregation of poly-glutamic acid based polypeptides.

Department of Chemical Engineering, University of California Berkeley, Berkeley, CA 94720, United States.
Biophysical Chemistry (Impact Factor: 2.28). 09/2008; 136(2-3):74-86. DOI: 10.1016/j.bpc.2008.04.008
Source: PubMed

ABSTRACT The aggregation of two negatively-charged polypeptides, poly-L-glutamic acid (PE) and a copolymer of poly-glutamic acid and poly-alanine (PEA), has been studied at different peptide and salt concentrations and solution pH conditions. The kinetics of aggregation were based on Thioflavin T (ThT) fluorescence measurements. The observed lag phase shortened and the aggregation was faster as the pH approached the polypeptides' isoelectric points. While the initial polypeptide structures of PE and PEA appeared identical as determined from circular dichroism spectroscopy, the final aggregate morphology differed; PE assumed large twisted lamellar structures and the PEA formed typical amyloid-like fibrils, although both contained extensive beta-sheet structure. Differences in aggregation behavior were observed for the two polypeptides as a function of salt concentration; aggregation progressed more slowly for PE and more quickly for PEA with increasing salt concentration. Several models of aggregation kinetics were fit to the data. No model yielded consistent rate constants or a critical nucleus size. A modified nucleated polymerization model was developed based on that of Powers and Powers [E.T. Powers, D.L. Powers, The kinetics of nucleated polymerizations at high concentrations: Amyloid fibril formation near and above the "supercritical concentration", Biophys. J. 91 (2006) 122-132], which incorporated the ability of oligomeric species to interact. This provided a best fit to the experimental data.

1 Bookmark
 · 
95 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abnormal protein aggregates, so called amyloid fibrils, are mainly known as pathological hallmarks of a wide range of diseases, but in addition these robust well-ordered self-assembled natural nanostructures can also be utilized for creating distinct nanomaterials for bioelectronic devices. However, current methods for producing amyloid fibrils in vitro offer no spatial control. Herein, we demonstrate a new way to produce and spatially control the assembly of amyloid-like structures using an organic electronic ion pump (OEIP) to pump distinct cations to a reservoir containing a negatively charged polypeptide. The morphology and kinetics of the created proteinaceous nanomaterials depends on the ion and current used, which we leveraged to create layers incorporating different conjugated thiophene derivatives, one fluorescent (p-FTAA) and one conducting (PEDOT-S). We anticipate that this new application for the OEIP will be useful for both biological studies of amyloid assembly and fibrillogenesis as well as for creating new bioelectronic nanomaterials and devices.
    Small 10/2010; 6(19):2153-61. · 7.82 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Traditional simulation and analysis of amyloid aggregation kinetics has involved the examination of a single lumped parameter taken to reflect the total mass of protein in amyloid form. However use of increasingly sophisticated multi-experimental strategies capable of providing information on the structure of the growing fibril at the mesoscopic and atomistic level, has put extra information within the experimenter's reach. Although such data can be presented empirically, its incorporation into a theoretical model is more problematic due to scaling issues associated with modern day approaches which fall into either the particle based or statistical based categories. Here we present a coarse grained multi-scale simulation of irreversible amyloid formation that straddles this simulation divide by using a set of theory derived size and conformation specific rate constants to simulate the kinetic evolution of the amyloid fibril population. This approach represents a potentially profitable simulation/analytical strategy that will help to probe more deeply into the underlying molecular driving forces behind the phenomenon of amyloid formation.
    Biophysical chemistry 01/2009; 140(1-3):122-8. · 2.28 Impact Factor

Full-text

View
1 Download
Available from