Imparting Albumin-Binding Affinity to a Human Protein
by Mimicking the Contact Surface of a Bacterial Binding Protein
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Abstract
Attachment of a bacterial albumin-binding
protein module is an
attractive strategy for extending the plasma residence time of protein
therapeutics. However, a protein fused with such a bacterial module
could induce unfavorable immune reactions. To address this, we designed
an alternative binding protein by imparting albumin-binding affinity
to a human protein using molecular surface grafting. The result was
a series of human-derived 6 helix-bundle proteins, one of which specifically
binds to human serum albumin (HSA) with adequate affinity (<i>K</i><sub>D</sub> = 100 nM). The proteins were designed by transferring
key binding residues of a bacterial albumin-binding module, Finegoldia magna protein G-related albumin-binding
domain (GA) module, onto the human protein scaffold. Despite 13β15
mutations, the designed proteins maintain the original secondary structure
by virtue of careful grafting based on structural informatics. Competitive
binding assays and thermodynamic analyses of the best binders show
that the binding mode resembles that of the GA module, suggesting
that the contacting surface of the GA module is mimicked well on the
designed protein. These results indicate that the designed protein
may act as an alternative low-risk binding module to HSA. Furthermore,
molecular surface grafting in combination with structural informatics
is an effective approach for avoiding deleterious mutations on a target
protein and for imparting the binding function of one protein onto
another