Host interaction functions of LIC_10902 and LIC_20185 highlight the multifactorial nature of Leptospira interrogans pathogenesis

Leptospirosis is a neglected global zoonosis caused by pathogenic Leptospira, which rely on a vast repertoire of outer membrane proteins (OMPs) to mediate tissue colonization and immune evasion. Despite being usually associated with regulation of gene expression of iron transport system proteins, FecR domain-containing proteins seem to possess a multifunctional role for Leptospira. This study characterizes two FecR proteins from L. interrogans serovar Copenhageni, LIC_10902 and LIC_20185, previously predicted as hypothetical proteins. Target proteins were analysed in silico for cloning parameters obtention and structural analysis. Target protein genes were amplified from L. interrogans sv. Copenhageni genome, cloned in the pAE vector and recombinant proteins were produced in Escherichia coli BL21 Star (DE3) pLysS. Recombinant protein purification was achieved by metal affinity chromatography and purified recombinant proteins were structurally characterized by circular dichroism (CD), and their immunogenicity and role in host-pathogen interactions were evaluated by ELISA. Analysis shows these proteins are conserved among pathogenic species and suggested that both contain a β-sheet-rich FecR domain. Purified recombinant proteins were produced in Escherichia coli. In vitro, rLIC_20185 bound elastin and E-cadherin, while both proteins interacted with plasminogen (PLG), vitronectin (VT), and complement components C4b, C7, C8, and C9. Experiments with LIC_10902 fragments indicated that the FecR domain mediates C8, C9, and PLG binding. Furthermore, both proteins inhibited in vitro C9 polymerization, and their interaction with PLG enabled its activation into plasmin (PLA). Although production in non-pathogenic L. biflexa serovar Patoc (LbP) did not increase resistance to normal human serum (NHS), our results collectively suggest that both proteins could mediate pathogen-host interactions and potentially contribute to tissue adhesion and immune evasion.