Self-Assembly of Synthetic and Biological Polymeric Systems of ...

6.7.- Relevant aspects on the HSA fibril formation
I. HSA has the ability to self-assemble into amyloid-like aggregates under different
solution conditions, i.e., under both physiological and acidic pH at elevated
temperature and different ionic strengths. Under these solution conditions, the HSA
native state is destabilized generating partially folded states that can aggregate to
form fibrils.
II. At physiological pH, fibrillation is progressively faster and more efficient in the
presence of up to 50 mM NaCl due to electrostatic shielding. ThT fluorescence, CD, FT-
IR and Trp fluorescence spectra confirm the structural changes in both tertiary and
secondary structure along the HSA fibrillation process. In this way, large extents of β-
sheet structure at large salt concentrations are also corroborated from the analysis of
far UV-CD spectra.
III. Under acidic conditions, a progressive enhancement of HSA fibrillation is observed as
electrolyte concentration in solution increases.
IV. The fibrillation process of HSA does not show a lag-phase growth, except at acidic pH
in the absence of NaCl. The HSA fibrillation is a downhill process which does not
require a highly organized and unstable nucleus, with a progressive increase of the β-
sheet (up to 26%) and an unordered conformation at the expense of the α-helical
conformation.
V. The fibrils obtained show a curly morphology and differ in length. Besides,
suprafibrillar assemblies (spherulites and fibrillar gels) formed by the protein human
serum albumin under different solution conditions.
VI. Upon incubation at 65 0 C at both acidic (pH 2.5) and physiological (pH 7.4) pH in the
presence of different amounts of added electrolyte, suprafibrillar assemblies,
spherulites and fibrillar gels, are formed under different solution conditions. Fibrillar
gels are formed through intermolecular nonspecific association of amyloid fibrils.
Meanwhile, at a pH close to the isoelectric point of HSA (pH 5.5), particulate gels were
observed as a consequence of a faster protein aggregation, which does not allow the
necessary structural reorganization to enable the formation of more ordered
structures.
VII. Within spherulites, fibrils display a radial arrangement around a disorganized protein
core with sizes of several micrometers, as revealed by POM and confocal microscopy.
VIII. Protein structure destabilization and subsequent aggregation (into amorphous or well-
defined structured aggregates) were conditioned by the experimental pH,
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