Rotational allomerism and divergent evolution of domains in immunoglobulin light chains

Gel electrophoresis and molecular sieve chromatography were used to compare 17 different human KI type Bence Jones proteins including 5 for which the amino acid sequence is known. Although electrophoresis in the presence of NaDodSO4 showed uniformity of covalent dimer and monomer molecular weights, Sephadex chromatography under nondissociating conditions showed that monomers eluted with different apparent molecular weights. These differences were attributed to heterogeneity in light chain self-association; dimerization constants of the 17 proteins, calculated from a computer simulation of their behavior upon gel filtration, ranged from <103 to >106 M-1. The variable region, more specifically the third hypervariable region, appears to be responsible for the variation in the dimerization constant. Association properties of light chains of known sequence suggest that the presence of an aromatic or hydrophobic residue at position 96 enhances dimer formation whereas a charged residue at that position results in light chains remaining stable monomers. The location of hypervariable residue 96 within the amino-terminal portion of the joining segment of the variable region suggests that the joining region may account for the variability of selfassociation of light chains and, moreover, that it has a function in determining the selective association of immunoglobulin polypeptide chains.Studies on the physical and chemical properties of Bence Jones proteins-the homogeneous counterparts of immunoglobulin light chains-have provided considerable information concerning the structural basis for the generation of antibody diversity (1). Sequence analysis of K and X type Bence Jones proteins has revealed that light chains possess a primary structure characterized by variation in sequence among the first 107 amino-terminal residues, the variable half of the light chain (VL), and by a relatively invariant sequence of the ;107 carboxy-terminal residues, the constant half (CL). The VL consists of framework and hypervariable regions. Four subgroups of K chains and five subgroups of X chains have been defined structurally and immunochemically by the framework sequence homologies. The three hypervariable segments (HV1, HV2, HV3) contribute to the antigen-binding site (2).The VL and CL are under separate genetic control; recent studies of murine Bence Jones proteins indicate that the VL is encoded by two gene segments. One, the V gene, determines the sequence of the first t95 amino-terminal residues; the second, the joining (J) gene, determines the sequence of -10-12 carboxyl-terminal VL residues (3-6). The joining (J) segment of the V region contains a portion of segment HV3; thus, it contributes directly to the sequente diversity of the antigenbinding site. Its other functions, if any, have not as yet been determined. Whereas X Bence Jones proteins and light chains exist primarily as disulfide-linked covalent dimers, K Bence Jones proteins and light chains occur more commonly in the form of noncovalent dimers, stable monomers, ...

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confidence: 99%

Self-association of human immunoglobulin kappa I light chains: role of the third hypervariable region.

Stevens¹,

Westholm²,

Solomon³

et al. 1980

“…Likewise, an almost invariant proline (32) in the immunoglobulin family, corresponding to proline-210 in HLA-H3, is matched by arginine-108 in HLA-H2. Despite these dissimilarities, it is worth reiterating that variable immunoglobulin domains do not exhibit obvious similarity, in primary structure, to the constant domains; yet the three-dimensional structures of variable and constant domains are quite similar (33)(34)(35)(36)(37).…”

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confidence: 99%

Complete amino acid sequence of pooled papain-solubilized HLA-A, -B, and -C antigens: relatedness to immunoglobulins and internal homologies.

Trägårdh¹,

Rask²,

Wiman³

et al. 1980

Pooled, papain-solubilized HLA-A, -B, and -C antigens, derived from a large number of individuals and comprising several allelic forms, have been subjected to amino acid sequence determination. Despite the heterogeneity of the material, a main sequence representing all of the 273 amino acid residues could be established. The primary structure encompasses two immunoglobulin-like disulfide loops. The 32-microglobulin (4-6), and a 45,000-dalton, membrane-integrated, glycosylated heavy chain (7). The genetic polymorphism is in the amino acid sequence, but no information is available on the correlation between the variable amino acids and the serological specificities. Because immunological, chemical, and physical analyses strongly suggest that the overall conformation of the HLA antigens is similar regardless of the allelic form, it is conceivable that the amino acid variability occurs in discrete region(s) of the molecule that do not influence the overall conformation (8). This would be analogous to the situation for antibodies in which the hypervariable regions are clustered to form the antigenbinding site (9).frMicroglobulin is homologous to immunoglobulin constant domains (10). However, the amino acid sequence variability among the various HLA antigen specificities occurs in the heavy chain. Limited amino acid sequence information on murine (11) and hum4n (12, 13) transplantation antigen heavy chains generated claims for homologies with immunoglobulins. As more data became available it was evident that the HLA antigen heavy chains contained at least one region displaying obvious sequence homology with 32-microglobulin and the constant immunoglobulin domains (14-17).In a previous communication we outlined the amino acid sequence of about one-third of the HLA antigen heavy chain and showed that this portion of the molecule was similar to immunoglobulins (16). We have now completed determining The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 (18). Because the starting material was heterogeneous, multiple amino acid residues were encountered in several positions. Here, the main sequence-i.e., the quantitatively dominating residue at each position-has been used in the computer analyses.In the statistical analyses, the use of amino acid residues occurring in smaller amounts than in the main residue did not change the overall results of the computer analyses.Statistical Analyses for Relatedness to Other Proteins. The amino acid sequence of the HLA antigen heavy chain was compared to known sequences, maintained in a protein sequence data file (19), by using the SEARCH program (20). An input matrix, the mutation data matrix (250 PAM) (21), and a matrix bias parameter, B = 2, were supplied to the program. To analyze the homology between the HLA antigen heavy chain and 32-microglobulin and the IgG variable and constant domains, the RELATE program was used (22, t). Program ALIGN ...

“…We have also proposed (8) that each hapten bound to L2 315 interacts with residues of both light chains of the dimer in a fashion analogous to the interaction of complementarity residues of sites present in HL (1,5,7,(25)(26)(27). This, together with the similarity between the interchain interaction in the Fab and L2 mentioned above (1,3,4,26), raises the possibility that similar conformational transitions are induced in the native Fab upon hapten binding. Such changes may not be resolved by static binding measurements because the Fab usually binds only one hapten per two chains (8,28).…”

Section: Resultsmentioning

confidence: 89%

“…These properties of the light chain dimer make it a potential model for the receptors present on thymus-derived lymphocytes. A close structural homology between the Fab fragment and the light chain dimer (L2) of immunoglobulins has been shown by x-ray crystallography (1)(2)(3)(4). This structural homology together with the hapten binding capacity of the L2s (1) led to the suggestion that they are a model of a primitive antibody, which could have existed prior to the divergence of independent light and heavy chains (1,2,5).…”

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confidence: 99%

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

Zidovetski¹,

Licht²,

Pecht³

1979

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.