Cholera toxin A1 residues single alanine substitutional mutation and effect on activity with stimulatory G protein

Abstract

Cholera is a well-known gastrointestinal infection. The cholera toxin is an important pathological substance in pathogenesis of cholera diarrhea. Cholera toxin is composed of catalytic A1 subunit, an A2 linker, and a homopentameric cell-binding B subunit. In enterocyte, cholera toxin will attach to GM1 ganglioside receptors on the apical membrane and causes retrograde vesicular trafficking to endoplasmic reticulum. At endoplasmic reticulum, cholera toxin A1 is released from the rest of the toxin into cytoplasm. The cholera toxin A1 interacts will catalyze ADP ribosylation of subunits of stimulatory G protein resulting a persistent activation of adenylate cyclase and an elevation of intracellular cAMP which further result in diarrhea. The single alanine substitutional mutation can result in the reduction of the interaction activity between cholera toxin A1 and stimulatory G protein. In this study, the four well-known mutations, H55, R67, L71, S78, or D109, of cholera toxin A1 is focused. The author hereby calculates for the reaction energy for the reaction between cholera toxin A1 and stimulatory G protein in naïve case and mutated case. To calculate, the standard bonding energy calculation technique in mutation analysis was used. It can be seen that aberrant in reaction energy in each studied mutation is different and can imply the different effect on activity with stimulatory G protein.