Effect of interchain disulfide bond on hapten binding properties of light chain dimer of protein 315.

Abstract

The hapten binding characteristics of the covalent light chain dimer, derived from the murine IgA secreted by plasmacytoma MOPC-315, to two nitroaromatic compounds, epsilon-N-(2,4-dinitrophenyl)-L-lysine and 4-(alpha-N-alanine)-m-nitrobenz-2-oxa-1,3-diazole, were investigated by differential spectroscopic titrations. The binding curves for both haptens were found to display sigmoidity similar to that reported earlier for the reduced and alkylated dimer held together by noncovalent bonds only. However, the presence of the interchain disulfide bond in the covalent dimer was found to cause marked changes in its binding properties. The data, like those obtained for the noncovalent dimer, fit the allosteric model of Monod, Wyman, and Changeux in which binding of the first hapten to the dimer causes a conversion of both sites of the protein molecule from a lower to a higher affinity conformation. However, the binding parameters show that both the affinity and the positive cooperativity in the interaction between haptens and the covalent dimer are significantly enhanced. The differences in the parameters of the binding and of the allosteric transition caused by the presence of the interchain disulfide bond demonstrate the existence of longitudinal interactions in immunoglobulin derivatives. These properties of the light chain dimer make it a potential model for the receptors present on thymus-derived lymphocytes.

A heterologous immunoglobulin chain recombinant carries a distinct site for dinitrophenyl and obeys the common hapten binding mechanism

“…The shape of the spectrum of the H460L315-DNPL complex is significantly different from those of either of its parent proteins, insert). Moreover, a different shape is also displayed by the complexes of DNPL with different light-chain derivatives of protein 315: light-chain dimer with the reduced and alkylated inter-light-chain disulfide bond, L2ncov (Lancet et al, 1977), light-chain dimer with this disulfide bond intact, L2c0v (Zidovetzki et al, 1979), and the dimer of with DNPL vs. free DNPL at 7 °C. The protein concentration was 1.56 X 10~5 M sites.…”

“…Indeed, the dimers of the light chains of this protein were shown to bind nitroaromatic haptens with the stoichiometry of two hapten molecules per dimer and the same fine specificity as the parent protein (Schechter et al, 1976;Licht et al, 1977). In view of this, it is noteworthy that the absorption spectrum of the h460L315-DNPL complex (Figure 2) is significantly different from those exhibited by the complexes of DNPL with the light chain dimers or with either of its two parent proteins (Lancet et al, 1977;Zidovetzki et al, 1979). All the spectra mentioned above show a charge-transfer band considered as a characteristic feature due to the interaction of the DNP ring with an indole group (Trp-93 of L315; Padlan et al, 1976;Zidovetzki et al, 1981b) in the binding site.…”

Analysis of the structural correlates for antibody polyreactivity by multiple reassortments of chimeric human immunoglobulin heavy and light chain V segments.

“…Other L chains have been shown to not only contribute to Ag specifidty of polyreactivity but also to efficiently bind Ags independently of H chains. Dimers of the MOPC 315 L chain bind e-N-(2,4 dinitrophenyl)-t.-lysine and 4-(ot-N-alanine)-7-nitrobenz-2-oxa-1, 3-diazide (42,43); and dimers of the L chain Bence-Jones Mcg protein bind dinitrophenyl compounds, e-dansyUysine, colchichine, 1,10-phenanthroline, methadone, morphine, meperidine, 5-acetyluracil, caffeine, theophylline, menadione (vitamin K3), triacetin, and other compounds (44,45). In the case of mAb55, the direct multiple Ag-binding activity of the V~325 segment remains to be defined as this V~ segment failed to generate a polyreactive Ab when paired with the V, segment of mAbl3.…”

Marked structural differences of the Mcg Bence-Jones dimer in two crystal systems

“…When conformational changes are induced in the dimer by the binding of haptenlike molecules [e.g., bis(dinitrophenyl)lysine], the interchain disulfide bond locks the protein in a stable, but abnormal form which only crystallizes as needles in ammonium sulfate (Firca et al, 1978;Ely et al, 1978a). These changes can be reversed by cleavage and slow reoxidation of the interchain disulfide bond, whereupon the normal trigonal crystal form is produced in ammonium sulfate [for recent solution studies on the effect of the interchain disulfide bond on the hapten-binding properties of the MOPC-315 light-chain dimer, see Zidovetzki et al (1979)].…”