Leptospirosis is a global zoonotic infectious disease caused by Leptospira interrogans. The pathogen rapidly invades into hosts and diffuses from bloodstream into internal organs and excretes from urine to cause transmission of leptospirosis. However, the mechanism of leptospiral invasiveness remains poorly understood.
Proteolytic activity of M16-type metallopeptidases (Lep-MP1/2/3) of L. interrogans was determined by spectrophotometry. Expression and secretion of Lep-MP1/2/3 during infection of cells were detected by qRT-PCR, Western Blot assay and confocal microscopy. Deletion and complementation mutants of the genes encoding Lep-MP1/2/3 were generated to determine the roles of Lep-MP1/2/3 in invasiveness using transwell assay and virulence in hamsters.
L. interrogans but not saprophytic L. biflexa strains were detectable for Lep-MP-1/2/3-encoding genes. rLep-MP1/2/3 hydrolyzed ECM proteins, but rLep-MP1/3 displayed stronger proteolysis than rLep-MP2, with 123.179/340.136 µmol•L-1 Km and 0.154/0.159 s-1 Kcat values. Expression, secretion and translocation of Lep-MP1/2/3 during infection of cells were increased. ΔMP1/3 but not ΔMP2 mutant presented attenuated transmigration through cell monolayers, decreased leptospiral loading in the blood, lungs, liver, kidneys and urine, and 10/13-fold-decreased LD50 and milder histopathologic injury in hamsters.
Lep-MP1/3 are involved in virulence of L. interrogans in invasion into hosts and diffusion in vivo, and transmission of leptospirosis.

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