7ST8

Crystal structure of 7H2.2 Fab in complex with SAS1B C-terminal region

Summary for 7ST8

• Entry DOI: 10.2210/pdb7st8/pdb
• Descriptor: 7H2.2 Fab Heavy Chain, 7H2.2 Fab Light Chain, Astacin-like metalloendopeptidase, ... (4 entities in total)
• Functional Keywords: cancer, antibody, oocyte antigen, immune system
• Biological source: Mus musculus; More
• Total number of polymer chains: 3
• Total formula weight: 64900.09

Authors

Legg, M.S.G.,Evans, S.V. (deposition date: 2021-11-12, release date: 2022-05-11, Last modification date: 2024-10-23)

Primary citation

Legg, M.S.G.,Gagnon, S.M.L.,Powell, C.J.,Boulanger, M.J.,Li, A.J.J.,Evans, S.V.
Monoclonal antibody 7H2.2 binds the C-terminus of the cancer-oocyte antigen SAS1B through the hydrophilic face of a conserved amphipathic helix corresponding to one of only two regions predicted to be ordered
Acta Crystallogr.,Sect.D, 78:623-632, 2022

PubMed Abstract: The structure of the antigen-binding fragment (Fab) of mouse monoclonal antibody 7H2.2 in complex with a 15-residue fragment from the metalloproteinase sperm acrosomal SLLP1 binding protein (SAS1B), which is a molecular and cellular candidate for both cancer therapy and female contraception, has been determined at 2.75 Å resolution by single-crystal X-ray diffraction. Although the crystallization conditions contained the final 148 C-terminal residues of SAS1B, the Fab was observed to crystallize in complex with a 15-residue fragment corresponding to one of only two elements of secondary structure that are predicted to be ordered within the C-terminal region of SAS1B. The antigen forms an amphipathic α-helix that binds the 7H2.2 combining site via hydrophilic residues in an epitope that spans the length of the antigen α-helix, with only two CH-π interactions observed along the edge of the interface between the antibody and antigen. Interestingly, the paratope contains two residues mutated away from the germline (YL32F and YH58R), as well as a ProH96-ThrH97-AspH98-AspH99 insertion within heavy chain CDR3. The intact 7H2.2 antibody exhibits high affinity for the SAS1B antigen, with 1:1 binding and nanomolar affinity for both the SAS1B C-terminal construct used for crystallization (3.38 ± 0.59 nM) and a 15-amino-acid synthetic peptide construct corresponding to the helical antigen observed within the crystal structure (1.60 ± 0.31 nM). The SAS1B-antibody structure provides the first structural insight into any portion of the subdomain architecture of the C-terminal region of the novel cancer-oocyte tumor surface neoantigen SAS1B and provides a basis for the targeted use of SAS1B.

PubMed: 35503210
DOI: 10.1107/S2059798322003011

Experimental method

X-RAY DIFFRACTION (2.75 Å)