Heparin Accelerates the Protein Aggregation via the Downhill Polymerization Mechanism: Multi-Spectroscopic Studies to Delineate the Implications on Proteinopathies

Abstract

Heparin is one of the members of the glycosaminoglycan (GAG) family, which has been associated with protein aggregation diseases including Alzheimer’s disease, Parkinson’s disease, and prion diseases. Here, we investigate heparin-induced aggregation of bovine serum albumin (BSA) using different spectroscopic techniques [absorption, 8-anilino-1-naphthalene sulfonic acid (ANS) and thioflavin T (ThT) fluorescence binding, and far- and near-UV circular dichroism]. Kinetic measurements revealed that heparin is involved in the significant enhancement of aggregation of BSA. The outcomes showed dearth of the lag phase and a considerable change in rate constant, which provides conclusive evidence, that is, heparin-induced BSA aggregation involves the pathway of the downhill polymerization mechanism. Heparin also causes enhancement of fluorescence intensity of BSA significantly. Moreover, heparin was observed to form amyloids and amorphous aggregates of BSA which were confirmed by ThT and ANS fluorescence, respectively. Circular dichroism measurements exhibit a considerable change in the secondary and tertiary structure of the protein due to heparin. In addition, binding studies of heparin with BSA to know the cause of aggregation, isothermal titration calorimetry measurements were exploited, from which heparin was observed to promote the aggregation of BSA by virtue of electrostatic interactions between positively charged amino acid residues of protein and negatively charged groups of GAG. The nature of binding of heparin with BSA is very much apparent with an appreciable heat of interaction and is largely exothermic in nature. Moreover, the Gibbs free energy change (ΔG) is negative, which indicates spontaneous nature of binding, and the enthalpy change (ΔH) and entropy change (ΔS) are also largely negative, which suggest that the interaction is driven by hydrogen bonding.

Effect of Trehalose and Ceftriaxone on the Stability of Aggregating-Prone Tau Peptide Containing PHF6* Sequence: An SRCD Study

“…As shown in Figure 6A, incubation with shaking of the tau peptide CD solution alone induces poor aggregation, and few amorphous aggregates were observed after one week of incubation (data not shown) according to the previous work of Mandelkow et al [35]. The TEM analysis of peptide-heparin CD solution incubated with shaking at 25 • C revealed a mesh of interwoven filaments with a typical amyloid morphology consisting of networks of long, unbranched fibers greater than 500 nm (Figure 6B), confirming the ability of heparin to induce peptide aggregation and fibrillation, acting as a structured template for peptide self-assembly [36].…”

“…The TEM analysis of peptide–heparin CD solution incubated with shaking at 25 °C revealed a mesh of interwoven filaments with a typical amyloid morphology consisting of networks of long, unbranched fibers greater than 500 nm ( Figure 6 B), confirming the ability of heparin to induce peptide aggregation and fibrillation, acting as a structured template for peptide self-assembly [ 36 ].…”

Structural Characterization and Binding Studies of the Ectodomain G Protein of Respiratory Syncytial Virus Reveal the Crucial Role of pH with Possible Implications in Host–Pathogen Interactions

“…ITC provides direct information regarding the interaction of the protein with the ligand. 38 , 39 The information obtained from ITC may help to explain the mechanism of binding of the virion with the host cell membrane. A one-site binding model was used to analyze the ITC thermogram data (at pH 7.5 and 298 K), which provided the best fit.…”

Impact of Single Amino Acid Substitutions in Parkinsonism-Associated Deglycase-PARK7 and Their Association with Parkinson’s Disease

“…The solubility of a protein influences its function to a great extent. Diseases such as Parkinson's disease, amyloidosis, and Alzheimer's disease are caused by the aggregation of insoluble parts of the proteins [30][31][32][33][34]. To predict the solubility of PARK7, we calculated the variants' solubility using SODA (Solubility based on Disorder and Aggregation).…”