The Terminal Immunoglobulin-Like Repeats of LigA and LigB of Leptospira Enhance Their Binding to Gelatin Binding Domain of Fibronectin and Host Cells

Abstract

Leptospira spp. are pathogenic spirochetes that cause the zoonotic disease leptospirosis. Leptospiral immunoglobulin (Ig)-like protein B (LigB) contributes to the binding of Leptospira to extracellular matrix proteins such as fibronectin, fibrinogen, laminin, elastin, tropoelastin and collagen. A high-affinity Fn-binding region of LigB has been localized to LigBCen2, which contains the partial 11th and full 12th Ig-like repeats (LigBCen2R) and 47 amino acids of the non-repeat region (LigBCen2NR) of LigB. In this study, the gelatin binding domain of fibronectin was shown to interact with LigBCen2R (KD = 1.91±0.40 µM). Not only LigBCen2R but also other Ig-like domains of Lig proteins including LigAVar7'-8, LigAVar10, LigAVar11, LigAVar12, LigAVar13, LigBCen7'-8, and LigBCen9 bind to GBD. Interestingly, a large gain in affinity was achieved through an avidity effect, with the terminal domains, 13th (LigA) or 12th (LigB) Ig-like repeat of Lig protein (LigAVar7'-13 and LigBCen7'-12) enhancing binding affinity approximately 51 and 28 fold, respectively, compared to recombinant proteins without this terminal repeat. In addition, the inhibited effect on MDCKs cells can also be promoted by Lig proteins with terminal domains, but these two domains are not required for gelatin binding domain binding and cell adhesion. Interestingly, Lig proteins with the terminal domains could form compact structures with a round shape mediated by multidomain interaction. This is the first report about the interaction of gelatin binding domain of Fn and Lig proteins and provides an example of Lig-gelatin binding domain binding mediating bacterial-host interaction.

Role for cis -Acting RNA Sequences in the Temperature-Dependent Expression of the Multiadhesive Lig Proteins in Leptospira interrogans

“…LigA and LigB may aid in the colonization of L. interrogans by binding with high affinity to components of the extracellular matrix (15)(16)(17)(18)(19). The Lig proteins may also facilitate dissemination by interacting with proteins that control hemostasis (19)(20)(21).…”

Solution structure of leptospiral LigA4 Big domain

“…The domains have identical N-terminal sequence, but their C termini are variable [10,11]. The importance of the C-terminal repeats of the immunoglobulin-like domains of LigA has been demonstrated, which is enhancing binding affinity to fibronectin [12]. It was reported that Calcium could bind Lig proteins and modulates fibronectin binding [10].…”

Interação de proteínas de membrana de Leptospira com os reguladores Fator H e C4BP do sistema complemento humano.

“…Lig proteins interact with numerous host molecules, notably proteins that mediate attachment to host tissues [22][23][24][25][26][27][28][29]. In this work, we show that these multifunctional leptospiral proteins Figure 7.…”

“…Moreover, they are upregulated during host infection [16,18,20,46]. These proteins interact with a diverse array of host molecules, including proteins of the extracellular matrix and the coagulation cascade [22][23][24][25][26][27][28][29]. Their functional plurality prompted us to investigate whether they would interact Figure 6.…”

“…Their expression is controlled by osmolarity, a key environmental signal that enhances binding of Leptospira to host cells [20,21]. They have been identified as extracellular matrix-binding proteins because they are able to interact with fibronectin, laminin, collagen, fibrinogen, elastin, and tropoelastin [22][23][24][25][26][27][28][29]. Because important virulence factors of many pathogens may interact with multiple host proteins, including coagulation cascade molecules, extracellular matrix components, and complement regulators, during infection, we decided to evaluate whether the Lig proteins would contribute to leptospiral immune evasion by interacting with host complement regulators.…”