1BBJ: Crystal Structure Of A Chimeric Fab' Fragment Of An Antibody Binding Tumour Cells

The crystal structure of a chimeric Fab' fragment of a monoclonal antibody is presented. The Fab' comprises the murine light chain and heavy chain variable domains of the carcinoma-binding antibody B72.3 fused to the constant domain of human kappa, and the first constant domain and hinge domain of human gamma 4, respectively. A model for the Fab' has been determined by molecular replacement and refined to a resolution of 3.1 A with an R-factor of 17.6%. The additional residues that distinguish a Fab' from a Fab fragment are seen to be disordered in the crystals. The H3 hypervariable loop is short and adopts a sharp hairpin turn in a conformation that results from an interaction between the lysine side-chain of H93 and the main-chain carbonyl group of H96. The remaining hypervariable loops display conformations similar to those predicted from the canonical structures approach, although loop H2 is apparently displaced by a salt-bridge formed between H55 Asp and the neighbouring H73 Lys. These and other features of the structure likely to be important in grafting the hypervariable loops to an otherwise human framework are discussed.
PDB ID: 1BBJDownload
MMDB ID: 48100
PDB Deposition Date: 1992/4/30
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 3.1  Å
Source Organism:
Homo sapiens
Similar Structures:
Biological Unit for 1BBJ: dimeric; determined by author and by software (PISA)
Molecular Components in 1BBJ
Label Count Molecule
Proteins (2 molecules)
Igg4-kappa B72.3 FAB (Light Chain)
Molecule annotation
Igg4-kappa B72.3 FAB (Heavy Chain)(Gene symbol: IGHG4)
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB