Cationic surfactant mediated fibrillogenesis in bovine liver catalase: a biophysical approach

Abstract

Protein aggregation into oligomers and mature fibrils are associated with more than 20 diseases in humans. The interactions between cationic surfactants dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) with varying alkyl chain lengths and bovine liver catalase (BLC) were examined by various biophysical approaches. The delicate coordination of electrostatic and hydrophobic interactions with protein, play imperative role in aggregation. In this article, we have reconnoitered the relation between charge, hydrophobicity and cationic surfactants DTAB and TTAB on BLC at pH 7.4 and 9.4 which are two and four units above pI, respectively. We have used techniques like turbidity, Rayleigh light scattering, far-UV CD, ThT, ANS, Congo red binding assay, DLS, and transmission electron microscopy. The low concentration ranges of DTAB (0–600 μM) and TTAB (0–250 μM) were observed to increase aggregation at pH 9.4. Nevertheless, at pH 7.4 only TTAB was capable of inducing aggregate. DTAB did not produce any significant change in secondary structure at pH 7.4 suggestive of the role of respective charges on surfactants and protein according to the pI and alkyl chain length. The morphology of aggregates was further determined by TEM, which proved the existence of a fibrillar structure. The surfactants interaction with BLC was primarily electrostatic as examined by ITC. Our work demystifies the critical role of charge as well as hydrophobicity in amyloid formation.

Keywords:

• amyloids
• Congo red
• dynamic light scattering
• electron microscopy
• surfactants

Acknowledgements

Mohsin Vahid Khan would like to thank University Grant Commission (UGC), New Delhi for providing financial assistance in the form of SRF as Basic Scientific Research (BSR) fellow. The authors would also like to thank the Interdisciplinary Biotechnology Unit, for providing instrumental facilities and University Sophisticated Instruments Facility (USIF), Aligarh Muslim University for providing the facility for TEM. The authors extend their appreciation to the International Scientific Partnership Program ISPP at King Saud University for funding the research work through ISPP# 0014.