2O5Z

Crystal structure of the 1E9 LeuH47Trp/ArgH100Trp Fab 5-beta-androstane-3,17-dione complex

Summary for 2O5Z

• Entry DOI: 10.2210/pdb2o5z/pdb
• Related: 2O5X 2O5Y
• Descriptor: chimeric antibody Fab 1E9-DB3, SULFATE ION, 5-BETA-ANDROSTANE-3,17-DIONE, ... (5 entities in total)
• Functional Keywords: immunoglobulin, chimeric fab, antibody engineering, evolution of ligand recognition, immune system
• Biological source: Mus musculus, Homo sapiens (house mouse, human); More
• Total number of polymer chains: 2
• Total formula weight: 51066.40

Authors

Verdino, P.,Wilson, I.A. (deposition date: 2006-12-06, release date: 2007-12-18, Last modification date: 2024-11-06)

Primary citation

Verdino, P.,Aldag, C.,Hilvert, D.,Wilson, I.A.
Closely related antibody receptors exploit fundamentally different strategies for steroid recognition.
Proc.Natl.Acad.Sci.Usa, 105:11725-11730, 2008

PubMed Abstract: Molecular recognition by the adaptive immune system relies on specific high-affinity antibody receptors that are generated from a restricted set of starting sequences through homologous recombination and somatic mutation. The steroid binding antibody DB3 and the catalytic Diels-Alderase antibody 1E9 derive from the same germ line sequences but exhibit very distinct specificities and functions. However, mutation of only two of the 36 sequence differences in the variable domains, Leu(H47)Trp and Arg(H100)Trp, converts 1E9 into a high-affinity steroid receptor with a ligand recognition profile similar to DB3. To understand how these changes switch binding specificity and function, we determined the crystal structures of the 1E9 Leu(H47)Trp/Arg(H100)Trp double mutant (1E9dm) as an unliganded Fab at 2.05 A resolution and in complex with two configurationally distinct steroids at 2.40 and 2.85 A. Surprisingly, despite the functional mimicry of DB3, 1E9dm employs a distinct steroid binding mechanism. Extensive structural rearrangements occur in the combining site, where residue H47 acts as a specificity switch and H100 adapts to different ligands. Unlike DB3, 1E9dm does not use alternative binding pockets or different sets of hydrogen-bonding interactions to bind configurationally distinct steroids. Rather, the different steroids are inserted more deeply into the 1E9dm combining site, creating more hydrophobic contacts that energetically compensate for the lack of hydrogen bonds. These findings demonstrate how subtle mutations within an existing molecular scaffold can dramatically modulate the function of immune receptors by inducing unanticipated, but compensating, mechanisms of ligand interaction.

PubMed: 18689687
DOI: 10.1073/pnas.0801783105

Experimental method

X-RAY DIFFRACTION (2.4 Å)