Extended low-resolution structure of a Leptospira antigen offers high bactericidal antibody accessibility amenable to vaccine design

Abstract

Pathogens rely on proteins embedded on their surface to perform tasks essential for host infection. These obligatory structures exposed to the host immune system provide important targets for rational vaccine design. Here, we use a systematically designed series of multi-domain constructs in combination with small angle X-ray scattering (SAXS) to determine the structure of the main immunoreactive region from a major antigen from Leptospira interrogans, LigB. An anti-LigB monoclonal antibody library exhibits cell binding and bactericidal activity with extensive domain coverage complementing the elongated architecture observed in the SAXS structure. Combining antigenic motifs in a single-domain chimeric immunoglobulin-like fold generated a vaccine that greatly enhances leptospiral protection over vaccination with single parent domains. Our study demonstrates how understanding an antigen’s structure and antibody accessible surfaces can guide the design and engineering of improved recombinant antigen-based vaccines.

Comparative screening of recombinant antigen thermostability for improved leptospirosis vaccine design

“…While Lig protein vaccine studies have not comprehensively examined the potential for single‐domain derived vaccines (Adler, ), vaccine immunogenicity against infectious agents, such as Respiratory syncytial virus and Zika, can be enhanced with increased stability (Rostad et al, ; Xie et al, ). In a recent Lig protein study, serum antibodies (Abs) from hamsters inoculated with either LigB10 or LigB10‐B7‐B7 ( T m > 50°C) produced a 15% higher enzyme‐linked immunosorbent assay (ELISA) signal than LigB7 ( T m < 37°C) when tested for binding to the injected antigen (Hsieh et al, ). LigB7 is likely to unfold rapidly after entering the host and present as distorted conformational or linear B‐cell epitopes before aggregating.…”

“…Single Ig‐like domains of LigB (LigB2–LigB12) from L. interrogans serovar Pomona (GenBankTM, FJ030916) were constructed as previously described (Hsieh et al, ; Manford et al, ). Single Ig‐like domains (LigA8–LigA13) and a double domain (LigA12–LigA13) from the variable region of LigA from L. interrogans serovar Pomona were similarly constructed.…”

“…Single Ig‐like domains (LigA8–LigA13) and a double domain (LigA12–LigA13) from the variable region of LigA from L. interrogans serovar Pomona were similarly constructed. Chimeric LigB7–LigB10 and LigA8–LigA13 constructs were created by the overlapping extension polymerase chain reaction to produce all six possible swapped genes from three protein segments as previously described (Hsieh et al, ). Briefly, boundaries between three segments—strand A–C, strand C′–F, and strand G–G′, were rationally determined based on the spatial arrangement of β sheets in the high‐resolution structure of LigB12 (PDB ID: 2MOG; Ptak et al, ).…”

“…Lig protein Ig‐like domain construct containing plasmids were transformed into E. coli Rosetta strain for expression and purification (Hsieh et al, ). Protein expression was induced with 1 mM isopropyl β‐ d ‐thiogalactopyranoside at 20°C for 16 hr.…”

“…Both LigA and LigB are composed of an N‐terminal anchor followed by a stretch of 12 or more homologous immunoglobulin‐like (Ig‐like) domains with structural similarity to adhesin domains from enterobacterial pathogens (Matsunaga et al, ; Palaniappan et al, ; Ptak et al, ). Recent studies have demonstrated that the Ig‐like domain region from LigB is arranged with an extended architecture and is highly accessible to interactions with host proteins (Hsieh et al, ). The exposed surfaces of Lig proteins can bind extracellular matrix (ECM) proteins to facilitate adhesion and dissemination throughout the host and can also bind factors involved in immune evasion (Breda et al, ; Castiblanco‐Valencia et al, ; Lin & Chang, ; Vieira et al, ).…”