Oral Presentation 14th Lorne Infection and Immunity 2024

Cysteine-dependent antigenic heterogeneity of Shigella flexneri autotransporter IcsA and implications in host immunity evasion (#4)

Jilong Qin 1 , Yaoqin Hong 1 , Renato Morona 2 , Makrina Totsika 1
  1. Centre for Immunology and Infection Control, School of Biomedical Sciences, Queensland University of Technology, Brisbane, QLD, Australia
  2. Department of Molecular and Biomedical Science, The University of Adelaide, Adelaide, SA, Australia

Shigella IcsA is a versatile surface virulence factor required for both early and late pathogenesis stages, extracellularly to intracellularly. Despite IcsA serving as a model Type V secretion system (T5SS) autotransporter to study host pathogen interactions, its detailed molecular architecture is poorly understood. Recently, IcsA was found to switch to a different conformation for its adhesin activity upon sensing of the host stimuli by Shigella Type III secretion system (T3SS). Here, we report that the single cysteine residue (C130) near the N-terminus of IcsA passenger has a role in IcsA adhesin activity.  We also show that the IcsA passenger (IcsAp) exists in multiple conformations, and the conformation populations are influenced by a central pair of cysteine residues (C375 and C379). Disruption of either or both central cysteine residues alters the exposure of epitopes to polyclonal anti-IcsA antibodies previously shown to block Shigella adherence, yet without loss of IcsA intracellular functions in actin-based motility (ABM). Anti-IcsA reactivity was restored when the IcsA paired cysteine substitution mutants were expressed in a ∆ipaD background with a constitutively active T3SS, highlighting an interplay between T3SS and T5SS. The work here uncovers a unique molecular switch empowered by centrally localised, short-spaced cysteine pairs in a Type V autotransporter that maintains IcsA’s conformational landscape to aid host immunity evasion.