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Insights into the stability of a therapeutic antibody Fab fragment by molecular dynamics and its stabilization by computational design

Codina, N; Zhang, C; Chakroun, N; Dalby, PA; (2019) Insights into the stability of a therapeutic antibody Fab fragment by molecular dynamics and its stabilization by computational design. BioRxiv: Cold Spring Harbor, NY, USA. Green open access

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Abstract

Successful development of protein therapeutics depends critically on achieving stability under a range of conditions, while retaining their specific mode of action. Gaining a deeper understanding of the drivers of instability across different stress conditions, will potentially enable the engineering of protein scaffolds that are inherently manufacturable and stable. Here, we compared the structural robustness of a humanized antibody fragment (Fab) A33 using atomistic molecular dynamics simulations under two different stresses of low pH and high temperature. RMSD calculations, structural alignments and contact analysis revealed that low pH unfolding was initiated through loss of contacts at the constant domain interface (CL-CH1), prior to CL domain unfolding. By contrast, thermal unfolding began with loss of contacts in both the CL-CH1 and variable domain interface (VL-VH), followed by domain unfolding of CL and also of VH, thus revealing divergent unfolding pathways. FoldX and Rosetta both agreed that mutations at the CL-CH1 interface have the greatest potential for increasing the stability of Fab A33. Additionally, packing density calculations found these residues to be under-packed relative to other inter-domain residues. Two salt bridges were identified that possibly drive the conformational change at low pH, while at high temperature, salt bridges were lost and reformed quickly, and not always with the same partner, thus contributing to an overall destabilization. Sequence entropy analysis of existing Fab sequences revealed considerable scope for further engineering, where certain natural mutations agreed with FoldX and Rosetta predictions. Lastly, the unfolding events at the two stress conditions exposed different predicted aggregation-prone regions (APR), which would potentially lead to different aggregation mechanisms. Overall, our results identified the early stages of unfolding and stability-limiting regions of Fab A33, which provide interesting targets for future protein engineering work aimed at stabilizing to both thermal and pH-stresses simultaneously.

Type: Working / discussion paper
Title: Insights into the stability of a therapeutic antibody Fab fragment by molecular dynamics and its stabilization by computational design
Open access status: An open access version is available from UCL Discovery
DOI: 10.1101/644369
Publisher version: https://doi.org/10.1101/644369
Language: English
Additional information: The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY 4.0 International license (http://creativecommons.org/licenses/by/4.0/).
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Biochemical Engineering
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10092103
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