Recombinant E.coli mxiH protein

The mxiH protein is a key structural component of the type III secretion system (T3SS) in Gram-negative bacteria, particularly in pathogens such as *Shigella* spp. and some strains of *Escherichia coli*. The T3SS is a syringe-like molecular apparatus that enables these bacteria to inject effector proteins directly into host cells, facilitating invasion, immune evasion, and intracellular survival. MxiH, a conserved homolog of the *Salmonella* PrgI and *Yersinia* YscF proteins, forms the major subunit of the T3SS needle. This ~9 kDa protein polymerizes into a helical filament that extends from the bacterial surface, serving as a conduit for effector translocation. Its structural flexibility and dynamic assembly are critical for sensing host contact and regulating effector delivery.

Recombinant mxiH protein is produced through heterologous expression systems (e.g., *E. coli*) for functional and structural studies. Researchers utilize it to investigate needle assembly mechanics, host-pathogen interactions, and immune responses. Structural analyses, including NMR and cryo-EM, have revealed its α-helical core and conserved residues essential for oligomerization. Notably, mxiH's immunogenic properties make it a potential target for vaccines or diagnostics against shigellosis, a major cause of dysentery. Challenges in working with recombinant mxiH include maintaining solubility and native conformation due to its intrinsic aggregation propensity. Studies leveraging this protein have advanced antimicrobial strategies aimed at disrupting T3SS function, offering alternatives to traditional antibiotics in an era of rising multidrug resistance.