Crystal Structure of a Bivalent Antibody Fab Fragment

Published

November 11, 2020

Author(s)

Salman Shahid, Mingming Gao, David Gallagher, Steven Foung, Zhen-Yong Keck, Thomas Fuerst, Roy Mariuzza

Abstract

We determined the crystal structure to 1.8 Å resolution of the Fab fragment of an affinity- matured human monoclonal antibody (HC84.26.5D) that recognizes the E2 envelope glycoprotein of hepatitis C virus (HCV). Unlike conventional Fabs, which are monovalent monomers, Fab HC84.26.5D assembles into a bivalent domain-swapped dimer in which the two VL/VH modules are separated by 25 Å. In solution, Fab HC84.26.5D exists predominantly as a dimer (80%) in equilibrium with the monomeric form of the Fab (20%). Dimerization is mediated entirely by deletion of a single residue, VHSer119, in the elbow region linking the VH and CH1 domains. In agreement with the crystal structure, dimeric Fab HC84.26.5D is able to bind two HCV E2 molecules in solution. This is only the second example of a domain-swapped Fab dimer from among >3,000 Fab crystal structures determined to date. Moreover, the architecture of the doughnut- shaped Fab HC84.26.5D dimer is completely different from that of the previously reported Fab 2G12 dimer. Bivalent domain-swapped Fab dimers engineered on the basis of HC84.26.5D may be useful in single-particle cryoEM as a means of doubling the size of conventional Fab–protein complexes.

Citation

Journal of Molecular Biology

Pub Type

Journals

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Keywords

antibody, Fab, domain swapping, structure

Citation

Shahid, S. , Gao, M. , Gallagher, D. , Foung, S. , Keck, Z. , Fuerst, T. and Mariuzza, R. (2020), Crystal Structure of a Bivalent Antibody Fab Fragment, Journal of Molecular Biology, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=930980 (Accessed November 28, 2025)