Kinetic Analysis of Amyloid Formation in the Presence of Heparan Sulfate

Abstract

A number of human diseases are associated with the conversion of proteins from their native state into well defined fibrillar aggregates, depositing in the extracellular space and generally termed amyloid fibrils. Heparan sulfate (HS), a glycosaminoglycan normally present in the extracellular matrix, has been found to be universally associated with amyloid deposits and to promote amyloid fibril formation by all studied protein systems. We have studied the impact of HS on the amyloidogenesis of human muscle acylphosphatase, monitoring the process with an array of techniques, such as normal and stopped-flow far-UV circular dichroism, thioflavin T fluorescence, static and dynamic light scattering, and atomic force microscopy. The results show that HS accelerates the conversion of the studied protein from the native state into the amyloidogenic, yet monomeric, partially folded state. They also indicate that HS does not simply accelerate the conversion of the resulting partially folded state into amyloid species but splits the process into two distinct pathways occurring in parallel: a very fast phase in which HS interacts with a fraction of protein molecules, causing their rapid aggregation into ThT-positive and ␤-sheet containing oligomers, and a slow phase resulting from the normal aggregation of partially folded molecules that cannot interact with HS. The HS-mediated aggregation pathway is severalfold faster than that observed in the absence of HS. Two aggregation phases are generally observed when proteins aggregate in the presence of HS, underlying the importance of a detailed kinetic analysis to fully understand the effect of this glycosaminoglycan on amyloidogenesis.

Role of Glycosaminoglycan Sulfation in the Formation of Immunoglobulin Light Chain Amyloid Oligomers and Fibrils

“…Without the ability to tag molecules and monitor the formation over time using methods that do not modify the process, we cannot rule out that other hypotheses are plausible. Recently, Motamedi-Shad et al (32) proposed that HS induces a new phase, which contains oligomers possessing a ␤-structure that are capable of forming fibrils. Our data support this hypothesis in the full-length LC protein and suggest that it is the ␤-structure of the oligomers in the presence of HS that produces the ThT fluorescence.…”

Structural Characterization of Heparin-induced Glyceraldehyde-3-phosphate Dehydrogenase Protofibrils Preventing α-Synuclein Oligomeric Species Toxicity

“…On the other hand, GAGs are present in most, if not all, types of amyloids inside and outside of the cells (24,25). In vitro, GAGs have proved to affect protein aggregation kinetics (26). We recently reported that sulfated GAGs, like heparin and heparan sulfates, are able to trigger GAPDH amyloid aggregation under pH and temperature physiological conditions (27).…”

Amyloid Formation in Human Islets Is Enhanced by Heparin and Inhibited by Heparinase

“…Heparin binds to human but not rodent IAPP (26) and promotes the fibrillogenesis of human IAPP (27), proIAPP (21) as well as other amyloidogenic species including amyloid-ß (Aß) (26). Heparin is thought to act as a scaffold for amyloid formation (28) and inhibits amyloid fibril de-polymerization (29). Amyloid formation by IAPP in the presence of heparin results in increased fibril density and compaction (30) and thioflavin T fluorescence (31).…”