Periplasmic Nanobody-APEX2 Fusions Enable Facile Visualization of Ebola, Marburg, and Mengla virus Nucleoproteins, Alluding to Similar Antigenic Landscapes among Marburgvirus and Dianlovirus.
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ABSTRACT: We explore evolved soybean ascorbate peroxidase (APEX2) as a reporter when fused to the C-termini of llama nanobodies (single-domain antibodies, sdAb; variable domains of heavy chain-only antibodies, VHH) targeted to the E. coli periplasm. Periplasmic expression preserves authentic antibody N-termini, intra-domain disulphide bond(s), and capitalizes on efficient haem loading through the porous E. coli outer membrane. Using monomeric and dimeric anti-nucleoprotein (NP) sdAb cross-reactive within the Marburgvirus genus and cross-reactive within the Ebolavirus genus, we show that periplasmic sdAb-APEX2 fusion proteins are easily purified at multi-mg amounts. The fusions were used in Western blotting, ELISA, and microscopy to visualize NPs using colorimetric and fluorescent imaging. Dimeric sdAb-APEX2 fusions were superior at binding NPs from viruses that were evolutionarily distant to that originally used to select the sdAb. Partial conservation of the anti-Marburgvirus sdAb epitope enabled the recognition of a novel NP encoded by the recently discovered M?nglà virus genome. Antibody-antigen interactions were rationalized using monovalent nanoluciferase titrations and contact mapping analysis of existing crystal structures, while molecular modelling was used to reveal the potential landscape of the M?nglà NP C-terminal domain. The sdAb-APEX2 fusions also enabled live Marburgvirus and Ebolavirus detection 24 h post-infection of Vero E6 cells within a BSL-4 laboratory setting. The simple and inexpensive mining of large amounts of periplasmic sdAb-APEX2 fusion proteins should help advance studies of past, contemporary, and perhaps Filovirus species yet to be discovered.
SUBMITTER: Sherwood LJ
PROVIDER: S-EPMC6521291 | biostudies-literature | 2019 Apr
REPOSITORIES: biostudies-literature
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