BSA and HSA protein amyloid aggregates: Comparison and design for potential applications

Maurya, S (2014) BSA and HSA protein amyloid aggregates: Comparison and design for potential applications. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

Protein mis-folding and aggregation result in many human diseases and some of these diseases are caused when the protein aggregation leads to amyloid formation (Chiti and Dobson, 2006). Amyloids are insoluble, fibrous and well organized protein aggregates having cross-β core structure (Chiti and Dobson, 2006, Nelson et al., 2005). Some of the examples of amyloid-associated diseases include: Alzheimer’s disease, Prion disease, and Huntington’s disease. The all-α helix, acidic and multi-domain proteins bovine serum albumin (BSA) and Human serum albumin (HSA) can also form amyloid aggregates in vitro at high temperatures (Holm et al., 2007, Juarez et al., 2009a). BSA and HSA have multi-functional in vivo roles like delivering major nutrients to the cells and isolating toxins from the cells as they possess many ligand binding sites. They have half-life of 19 days and ability to restore plasma (Wunder et al., 2003). These proteins have one free cysteine and share over 76% sequence similarity (Francis, 2010) ( Huang et al., 2004). Recently, these proteins have been used as a plasma expander and also as preferred drug delivery agents (Park, 2012). Amyloid aggregates can be either cytotoxic causing disease or they can be beneficial or functional in some cases. BSA/HSA amyloid aggregates are shown to be non-cytotoxic (Holm et al., 2007) and are not involved in causing amyloid diseases, thus a better understanding of their amyloid properties can help in finding any potential applications. The present work undertakes a comparative analysis of properties of BSA and HSA protein amyloid aggregates. It is found here that despite the very high sequence similarity and similar biochemical properties, the amyloid aggregates of BSA and HSA vary significantly in their properties and stabilities. Previously, conjugation of therapeutic proteins (eg. Interferon alfa 2b & human growth hormone) with HSA has been shown to increase their circulatory life span and hence their therapeutic period. Here, we hypothesized that conjugating a therapeutic protein or peptide to amyloid form of HSA would further extend the circulatory life as the amyloid clearance is expectedly slower. As a proof of the feasibility, we succeeded in cross-linking two HSA molecules via their one free-cysteine residues followed by converting them into amyloid-like aggregates. Further studies using amyloid converted heterodimer of HSA with a therapeutic protein could lead to potential applications if the hetero-dimer aggregates remain non-cytotoxic

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