Title
Affinity is an important determinant of the anti-trypanosome activity of nanobodies
Author
Faculty/Department
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences. Pharmacy
Publication type
article
Publication
Subject
Human medicine
Source (journal)
PLoS neglected tropical diseases
Volume/pages
6(2012) :11 , 8 p.
ISSN
1935-2735
Article Reference
e1902
ISI
000311888900030
Carrier
E-only publicatie
Target language
English (eng)
Full text (Publishers DOI)
Abstract
Background: The discovery of Nanobodies (Nbs) with a direct toxic activity against African trypanosomes is a recent advancement towards a new strategy against these extracellular parasites. The anti-trypanosomal activity relies on perturbing the highly active recycling of the Variant-specific Surface Glycoprotein (VSG) that occurs in the parasite's flagellar pocket. Methodology/Principal Findings: Here we expand the existing panel of Nbs with anti-Trypanosoma brucei potential and identify four categories based on their epitope specificity. We modified the binding properties of previously identified Nanobodies Nb_An05 and Nb_An33 by site-directed mutagenesis in the paratope and found this to strongly affect trypanotoxicity despite retention of antigen-targeting properties. Affinity measurements for all identified anti-trypanosomal Nbs reveal a strong correlation between trypanotoxicity and affinity (KD), suggesting that it is a crucial determinant for this activity. Half maximal effective (50%) affinity of 57 nM was calculated from the non-linear dose-response curves. In line with these observations, Nb humanizing mutations only preserved the trypanotoxic activity if the KD remained unaffected. Conclusions/Significance: This study reveals that the binding properties of Nanobodies need to be compatible with achieving an occupancy of >95% saturation of the parasite surface VSG in order to exert an anti-trypanosomal activity. As such, Nb-based approaches directed against the VSG target would require binding to an accessible, conserved epitope with high affinity.
E-info
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Full text (open access)
https://repository.uantwerpen.be/docman/irua/32e78c/130117.pdf