Title
Salt-regulated reversible fibrillation of Mycobacterium tuberculosis isocitrate lyase: Concurrent restoration of structure and activity
Author
Harish Shukla, Ranjeet Kumar, Amit Sonkar, Kalyan Mitra, Md. Sohail Akhtar, Timir Tripathi
Year
2017
Journal
International Journal of Biological Macromolecules
Abstract
Protein fibrillation is associated with a number of neurodegenerative diseases. Nevertheless, several proteins not related to disease can also form fibrils in vitro under specific conditions. In the present study, we demonstrate the reversible fibrillation of a globular protein that is modulated by salt under physiological pH. Mycobacterium tuberculosis Isocitrate lyase (MtbICL) is a crucial enzyme involved in the glyoxylate shunt and a potential drug target against M. tuberculosis infection. Under physiological pH, the enzyme self-assembles into a fibrillar structure in the absence of salt in vitro. The mature fibrillar structure of MtbICL is dynamic and restores its tetrameric structure as well as activity with the addition of salt. The kinetics of fibril formation was investigated spectroscopically using 8-Anilinonaphthalene-1-sulfonic acid (ANS). Further, Transmission electron microscopy (TEM) and Atomic force microscopy (AFM) imaging also confirmed the formation of elongated fibrils in the absence of salt. The results indicate the balance between stabilizing forces and the localized electrostatic repulsions destabilizing the tetrameric MtbICL is adjusted via ion shielding. Our result is in congruence of the hypothesis that amyloid formation is an intrinsic property of most, if not all natural proteins under an appropriate set of conditions.
Instrument
J-810
Keywords
Circular dichroism, Secondary structure, Protein folding, Chemical stability, Aggregation, Biochemistry