The novel leptospiral surface adhesin Lsa20 binds laminin and human plasminogen and is probably expressed during infection

ABSTRACT

Leptospirosis is an emerging infectious disease caused by pathogenic species of Leptospira. In this work, we report the cloning, expression, purification, and characterization of two predicted leptospiral outer membrane proteins, LIC11469 and LIC11030. The LIC11469 protein is well conserved among leptospiral strains, while LIC11030 was identified only in Leptospira interrogans. We confirmed by surface proteolysis of intact leptospires with proteinase K that these proteins are most likely new surface leptospiral proteins. The recombinant proteins were evaluated for their capacity to attach to extracellular matrix (ECM) components and to plasminogen. The leptospiral protein encoded by LIC11469, named Lsa20 (leptospiral surface adhesin of 20 kDa), binds to laminin and to plasminogen. The binding with both components was not detected when Lsa20 was previously denatured or blocked with anti-Lsa20 antibodies. Moreover, Lsa20 binding to laminin was also confirmed by surface plasmon resonance (SPR). Laminin competes with plasminogen for binding to Lsa20, suggesting the same ligand-binding site. Lsa20-bound plasminogen could be converted to enzymatically active plasmin, capable of cleaving plasmin substrate D-valyl-leucyl-lysine-p-nitroanilide dihydrochloride. Lsa20 was recognized by antibodies in confirmed-leptospirosis serum samples, suggesting that this protein is expressed during infection. Taken together, our results indicate that Lsa20 is a novel leptospiral adhesin that in concert with the host-derived plasmin may help the bacteria to adhere and to spread through the hosts.