Crystal properties as indicators of conformational changes during ligand binding of interconversion of Mcg light chain isomers
Crystals were prepared from samples of nonjovalent and covalently linked dimers previously isolated as intermediates and end products in the interconversion of conformational isomers of immunoglobulin light chains from the patient Mcg. In ammonium sulfate these dimers crystallized in the trigonal form characteristic of the native Bence-Jones protein and in an abnormal needle form associated with conformational changes in the vicinity of the interchain disulfide bond. Trigonal forms were compared with the native covalent dimer by difference Fourier analysis at 3.5-A resolution. The packing of molecules in the trigonal crystal lattice was examined in detail to determine the steric limitations governing chemical modifications, chemical modifications within crystals or in solutions slated for crystallization. When the modifications involved only the cleavage and alkylation of the interchain disulfide bond, the difference Fourier maps indicated only local conformational changes mainly in the COOH-terminal pentapeptide segment of monomer 2 of the dimer. When light chains were dissociated from heavy chains and reassembled into a dimer, there were changes in segments which interact to stabilize the V domain dimer. These changes, as well as the more extensive changes in the needle forms, could be reversed by dissolving the crystals, cleaving the interchain disulfide bond, and allowing it to reoxidize. The resulting proteins crystallized as trigonal forms indistinguishable from those of the native dimer. After the binding of two molecules of bis(dinitrophenyl)lysine and subsequent removal of the ligands by dialysis, the dimer crystallized only as needles.
- Research Organization:
- Argonne National Lab., IL
- OSTI ID:
- 6935125
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 17:1; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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