Inhibition of ricin A-chain (RTA) catalytic activity by a viral genome-linked protein (VPg)

Publication date: Available online 27 February 2019Source: Biochimica et Biophysica Acta (BBA) - Proteins and ProteomicsAuthor(s): Valentina R. Aitbakieva, Rahimah Ahmad, Shaneen Singh, Artem V. DomashevskiyAbstractRicin is a plant derived protein toxin produced by the castor bean plant (Ricinus communis). The Centers for Disease Control (CDC) classifies ricin as a Category B biological agent. Currently, there is neither an effective vaccine that can be used to protect against ricin exposure nor a therapeutic to reverse the effects once exposed. Here we quantitatively characterize interactions between catalytic ricin A-chain (RTA) and a viral genome-linked protein (VPg) from turnip mosaic virus (TuMV). VPg and its N-terminal truncated variant, VPg1–110, bind to RTA and abolish ricin's catalytic depurination of 28S rRNA in vitro and in a cell-free rabbit reticulocyte translational system. RTA and VPg bind in a 1 to 1 stoichiometric ratio, and their binding affinity increases ten-fold as temperature elevates (5 °C to 37 °C). RTA-VPg binary complex formation is enthalpically driven and favored by entropy, resulting in an overall favorable energy, ΔG = −136.8 kJ/mol. Molecular modeling supports our experimental observations and predicts a major contribution of electrostatic interactions, suggesting an allosteric mechanism of downregulation of RTA activity through conformational changes in RTA structure, and/or disruption of binding with the ribosomal stalk. Fluor...
Source: Biochimica et Biophysica Acta (BBA) Proteins and Proteomics - Category: Biochemistry Source Type: research