Abstract
Despite their importance for antibody architecture and design, the principles governing antibody domain stability are still not understood in sufficient detail. Here, to address this question, we chose a domain from the invariant part of IgG, the CH2 domain. We found that compared with other Ig domains, the isolated CH2 domain is a surprisingly unstable monomer, exhibiting a melting temperature of ∼44 °C. We further show that the presence of an additional C-terminal lysine in a CH2 variant substantially increases the melting temperature by ∼14 °C relative to CH2 WT. To explore the molecular mechanism of this effect, we employed biophysical approaches to probe structural features of CH2. The results revealed that Lys101 is key for the formation of three secondary structure elements: the very C-terminal β-strand and two adjacent α-helices. We also noted that a dipole interaction between Lys101 and the nearby α-helix, is important for stabilizing the CH2 architecture by protecting the hydrophobic core. Interestingly, this interaction between the α-helix and C-terminal charged residues is highly conserved in antibody domains, suggesting that it represents a general mechanism for maintaining their integrity. We conclude that the observed interactions involving terminal residues have practical applications for defining domain boundaries in the development of antibody therapeutics and diagnostics.
Highlights
Despite their importance for antibody architecture and design, the principles governing antibody domain stability are still not understood in sufficient detail
chain 2 (CH2) variants in this study were extended by amino acids naturally occurring C terminally of the MAK33 CH2 domain, i.e. they connect it to the chain 3 (CH3) domain [14, 19] (Fig. 1, A and B)
We determined the impact of residues located C-terminally of the CH2 domain in IgG1 on its conformational stability and protein dynamics
Summary
Brandl‡, María Daniela Pulido Cendales§, Carolin Berner‡, Tejaswini Pradhan‡, Gina Maria Feind‡, Martin Zacharias§, Bernd Reif‡, and Johannes Buchner‡1 From the Center for Integrated Protein Science Munich, Departments of ‡Chemie and §Physik, Technische Universitat Munchen, 85748 Garching, Germany
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