Comparison of the amino acid sequences of the variable domains of two homogeneous rabbit antibodies to type III pneumococcal polysaccharide.

The amino acid sequences of the V (variable) regions of the H (heavy) and L (light) chains derived from rabbit antibody K-25, specific for type III pneumococci, were determined; this is the second homogeneous rabbit antibody besides antibody BS-5 whose complete sequence of the V domain has been established (Jaton, 1974d). The V regions of L chains BS-5 and K-25 (both of allotype b4) differ from each other by 19 amino acid residues; 11 of these 19 substitutions are located within the three hypervariable sections of the V region. On the basis of seven amino acid differences within the N-terminal 28 positions, it is suggested that L chain K-25 belongs to a different subgroup of rabbit K chains and L chain BS-5. H chain K-25 (allotype a2) differs from another H chain of the same allotype by one amino acid substitution within the N-terminal 70 positions in addition to interchanges occurring in the first two hypervariable sections. H chain K-25 was compared with H chain BS-5 (allotype a1) and with the known V-region rabbit sequences. Allotype-related differences between a1, a2 and a3 chains appear to occur within the N-terminal 16 positions and possibly in scattered positions throughout the V-region. In the hypervariable positions, variability between the two antibodies is remarkably more pronounced within the third hypervariable section of both H and L chains than within the first two.     

Allotype-related sequence variation of the heavy chain of rabbit immunoglobulin G

The heavy chain of rabbit immunoglobulin G exists in three major allotypic patterns, Aa1–Aa3. A comparison of the amino acid compositions of the heavy chains isolated from immunoglobulin IgG homozygous for each allotypic determinant revealed the presence of an additional methionine residue per chain in the Aa3 allotype relative to the Aa1 and Aa2 allotypes. The position of the additional methionine residue was determined by cyanogen bromide cleavage and by tryptic digestion of the γ-chains; it coincided with the inter-Fd–Fc area of the chain. Isolation and characterization of the corresponding tryptic peptides of 31 amino acid residues from each of the allotypes showed the presence of a methionine-for-threonine replacement in the Aa3 allotype, but only in about 70–80% of the molecules. No other allotypic variations were seen in this tryptic peptide. Allotypically related variations in composition were also detected in the N-terminal cyanogen bromide-cleavage peptide.     

Partial amino acid sequence and genetic control of latent a2 allotype induced in rabbits by immunization with anti-a2 antibody

We have shown that after immunization of homozygous a1 rabbits of the B immunoglobulin (Ig) heavy chain haplotype with anti-a2 antibody (Ab) a population of molecules appears that has all of the serologic characteristics of the a2 allotype. We have now isolated these putative latent a2 molecules, have separated the heavy chains, and after enzymatic deblocking, have determined the first 19 N-terminal amino acids. For all eight allotype-associated residues, these putative latent a2 molecules have the amino acid residues typical of a2 allotype. As expected, the preimmune IgG from this a1a1 rabbit has the amino acids typical of the a1 allotype. Thus by partial amino acid sequence analysis, we provide additional evidence that the latent a2 allotype can be induced in a1a1 rabbits of the B heavy chain haplotype by immunization with anti-a2 Ab. Rabbits of other heavy chain haplotypes were also immunized with anti-a2 Ab and were tested for their ability to synthesize latent a2 allotype. Thus far, a1a1 rabbits of the A, B, C, and I heavy chain haplotypes all synthesize latent a2 allotype. In contrast, a3a3 rabbits of the G and H heavy chain haplotypes did not synthesize latent a2 allotype.     

Amino acid sequence of the N-terminal sixty-nine residues of heavy chain derived from a homogeneous rabbit antibody

The sequence of the N-terminal 69 residues of heavy chain from a homogeneous rabbit antibody to type III pneumococcal polysaccharide was determined. The sequence is similar to that found in heavy chains of normal pooled rabbit immunoglobulins of the same allotype Aa1. Two regions of the homogeneous heavy chain (residues 35-46 and 62-69) are very similar to corresponding regions of heavy chains from rabbit Aa2 immunoglobulin, as well as from mouse, guinea-pig and human immunoglobulins. In contrast, residues 47-62 appear to be variable. Comparison in this section with another homogeneous anti-pneumococcal antibody (Strosberg et al., 1972) of related specificity and of the same allotype indicates sequence variation in at least three positions. An antibody to group C streptococcal carbohydrate of allotype Aa2 (Fleischman, 1971) differs by five amino acids in the same region of the heavy chain. Sequence variability between these three antibodies does not occur in homologous positions within this variable section. Allotype-related sequences could not be identified in section 34-65.     

Serologic and structural characterization of immunoglobulin chains secreted by rabbit-mouse hybridomas

Serologic and primary structural analyses of Ig chains secreted by several rabbit-mouse hybridomas have shown that these hybrid cells produce heavy (H) or light (L) chains identical to those isolated from rabbit sera. Two of the cell lines (7D2, 7D6) secreted rabbit H chains with a m.w. of 55,000 each of which expressed a full complement of variable and constant region allotypes (a3, d11, e15). These apparently normal rabbit H chains were secreted in a complex with a m.w. about 130,000, and serologic studies indicated that this complex contained a covalently linked mouse kappa L chain. Two other cell lines (4C1, 12F2) produced allotype b4 L chains with m.w. of 23,000 and 25,000, and a third (1D4P5) produced an allotype b5 L chain with a m.w. of 23,000. Serologic analyses indicated that the allotypes on these chains are equivalent to those expressed by normal rabbit Ig molecules. Partial amino acid sequence data obtained for the L chain products showed them to be typical of rabbit L chains, and to be significantly different from mouse L chains.     

Allotypically related sequences in the Fd fragment of rabbit immunoglobulin heavy chains

The sequence has been completed of the N-terminal 94 residues of the variable section of the Fd fragment of heavy chains from rabbit immunoglobulin G (IgG) of allotype As1. Most of the sequence of the same section from IgG of allotype Aa3 is also reported. These results, in conjunction with a substantial sequence of the variable region of allotype Aa2 reported elsewhere (Fleischman, 1971), show the presence of 16 positions (including six consecutive positions) in which the residue present correlates with the allotype. No allotype-related sequence variation has been found in the constant section of the Fd fragment. This evidence supports the view that two genes code for the heavy chain and it can be used as evidence in favour of somatic mutation as the origin of the variability in the sequence of the N-terminal section. The evolutionary origin of the ;a' locus allotypes of rabbit immunoglobulins remains obscure.     

Variation in the N-terminal sequence of heavy chains of immunoglobulin G from rabbits of different allotype

The sequences of the N-terminal peptides prepared by Pronase digestion of the heavy chain of rabbit immunoglobulin G of allotype Aa1, Aa2 and Aa3 were determined and were shown to be related to the allotype. An N-terminal fragment of about 34 residues was also prepared from the allotype heavy chains, by cleavage with cyanogen bromide; the yield varied with the allotype. The sequences of the cyanogen bromide fragments from the Aa1 and Aa3 heavy chains contain allotype-related variations similar to those found in the N-terminal Pronase peptides, and these sequences are thought to be representative of the whole heavy-chain populations. There is about 60% homology between the two sequences, and superimposed on the differences between them there are a number of positions within each sequence at which at least two amino acids are present.     

Partial amino acid sequence of a rabbit immunoglobulin light chain of allotype b5

The amino acid sequence of a rabbit immunoglobulin light chain of allotype b5 has been nearly completed. A comparison of its structure with that of light chains of allotypes b4, b6, and b9 confirms that the constant regions of these various kappa chains differ by 20-35%. The substitutions are clustered in parts of the second half of the chain, and the b5 form bears more resemblance to the b6 chain than to any other, in good agreement with previous serological data. The analysis of the variable region reveals the existence of certain allotype-associated residues which have also been reported in other b5 chains, but not in proteins of the other allotypes. An examination of the rabbit light chain sequences between positions 96 and 107 suggests that this portion of the chain may be encoded separately by a joining "J" DNA segment, as has been described previously for murine and human immunoglobulins. In the rabbit, however, these J kappa regions appear to differ from one allotype to another. Together with the extensive variations of the constant regions, these data suggest that the rabbit kappa gene organization more closely resembles the murine gamma system (four different C gamma genes each flanked by its J segment) than the murine kappa system (a single C kappa gene).     

Nucleotide sequence of a rabbit IgG heavy chain from the recombinant F-I haplotype

We report the sequence of a cDNA encoding a rabbit immunoglobulin gamma heavy chain of d12 and e14 allotypes with high homology to partial cDNA sequences from rabbits of d11 and e15 allotypes. The encoded rabbit protein shows homologies with human (68-70%) and mouse (60-63%) gamma chains. The nucleotide sequence homologies of the CH domains range from 76-84% with human and 64-76% with mouse sequences. Comparison of the portion of VH encoding amino acid positions 34-112 with a previously determined VH sequence of the same allotype shows high conservation of sequences in the second and third framework segments but more marked differences both in length and encoded amino acids of the second and third complementarity-determining regions (CDRs). We also found a high degree of homology with a human genomic V-region, VH26 (77%) and a remarkable similarity between rabbit and human second CDR sequences and human genomic D minigenes. These results provide additional evidence that D minigene sequences share information with the CDR2 portion of VH regions.     

Sequence studies on the heavy chain of rabbit immunoglobulin A of different alpha-locus allotypes.

The amino acid sequence was determined of part of the variable region of heavy chain from rabbit immunoglobulin A of allotypes a1 and a3. Two corrections of the primary sequence of Aa1 gamma-chains are reported; most of the structural correlates of the alpha-locus allotypes are confirmed. The amino acid sequence of the N-terminal 20 residues of alpha-negative molecules was also determined and found to be homologous to the human VhIII subgroup. These molecules are present in a much higher proportion in the alpha-chain pool than in the gamma-chain.     

In vivo activation of quiescent B cells by anti-immunoglobulin. I. Induction of latent VH allotype production in adult rabbits by treatment with heterologous antibodies or antibody fragments

We demonstrated previously that injection of adult rabbits with homologous anti-VHa1 allotype antibody induces the appearance in serum of genetically unexpected (latent) a1 immunoglobulin (Ig) and a1-like internal images. We have now investigated the mechanism for this induction effect and have found that treatment of animals with polyclonal goat or monoclonal mouse anti-a1 antibody similarly results in production of unexpected a1 determinants. The N-terminal amino acid sequences of deblocked heavy chains showed that latent a1 Ig induced by monoclonal antibody treatment was identical to nominal a1 Ig at 18 of 19 residues, with the one amino acid difference at position 13 probably due to a single nucleotide change. Like nominal a1, these molecules expressed multiple VHa1 framework epitopes, as demonstrated by direct immunoelectron microscopic visualization of immune complexes. Whereas F(ab)'2 fragments of rabbit anti-a1 antibody retained inducing activity, F(ab) fragments were effective only when administered in an aggregated form; this result suggests that cross-linking of surface Ig receptors plays a critical role in the induction process. We conclude that all rabbits contain dormant B cells expressing germ-line-encoded latent allotypes, and that in vivo administration of anti-Ig antibody causes activation of these cells directly rather than through perturbation of an allotype regulatory network.     

Characterization and DNA sequence of the b6w2 allotype of the rabbit immunoglobulin kappa 1 light chain (b locus)

The b6w2 allotype of the constant region of the rabbit immunoglobulin kappa 1 (k1) light chain (b locus) was discovered in wild populations from northern Spain. At the serological level, the b6w2 allotype is characterized by the presentation of all b6-specific epitopes, while an allotypic determinant which is shared between the nominal b5 and b6 allotypes is lacking. The DNA fragment encoding the b6w2 allotype was amplified by means of the polymerase chain reaction, and sequenced directly by dideoxy-DNA-sequencing. When compared with the sequence of the nominal b6 allele, the b6w2 sequence differs at eleven nucleotide positions (96.5% similarity). This variation corresponds to amino acid replacements at 1) the three positions C-terminal to the peptidyl junction with the variable region (amino acid positions 109–111);2) the four positions N-terminal to the interdomain disulfide bond (167–170); and 3) two positions in the vicinity of the interchain disulfide bond (190 and 210). The nature and distribution of the observed nucleotide substitutions strongly suggest a possible role of the extra interdomain disulfide bond in the unusual evolutionary dynamics of the rabbit K1 light chain.The nucleotide sequence data reported in this paper have been submitted to the EMBL nucleotide sequence database and have been assigned the accession number Z48308     

Comparison of latent and nominal rabbit Ig VHa1 allotype cDNA sequences

The genetic basis for the expression of a latent VH allotype in the rabbit was investigated. VH region cDNA libraries were produced from spleen mRNA derived from a homozygous a2a2 rabbit expressing an induced latent VHa1 allotype and, for comparison, from a normal homozygus a1a1 rabbit expressing nominal VHa1 allotype. The deduced amino acid sequences of the nominal VHa1 cDNA were concordant with previously published VHa1 protein sequences. A comparison of two complete VH-DH-JH and six partial VHa1 sequences reveals highly conserved sequence within VH framework regions (FR) and considerable diversity in complementarity-determining regions and D region sequences. Two functional JH genes or alleles are evident. Amino acid sequencing of the N-terminal 15 residues of pooled affinity-purified latent VHa1 H chain showed complete sequence identity with the nominal VHa1 sequences. Possible latent VHa1-encoding cDNA clones, derived from the a2a2 rabbit, were selected by hybridization with oligonucleotide probes corresponding to the VHa1 allotype-associated segments of the first and third framework regions (FR1 and FR3). cDNA sequence analysis reveals that the 5' untranslated regions of nominal and latent VHa1 cDNA were virtually identical to each other and to previously reported sequences associated with VHa2 and VHa-negative genes. Moreover, some latent VHa1 genes encode FR1 segments that are essentially homologous to the corresponding segment of a nominal VHa1 allotype. In contrast, other putative latent genes display blocks of VHa1 sequence in either FR1 or FR3 that are flanked by blocks of sequence identical to other rabbit VH genes (i.e., VHa2 or VHa-negative). These composite sequences may be directly encoded by composite germ-line VH genes or may be the products of somatically generated recombination or gene conversion between genes encoding latent and nominal allotypes. The data do not support the hypothesis that latent genes are the result of extensive modification by somatic point mutation.     

Rabbit secretory components of different allotypes vary in their carbohydrate content and their sites of N-linked glycosylation

The asparagine-linked glycosylation sites in rabbit high and low Mr secretory components (SC) have been determined for the three known allotypes, t61, t62, and t63. Purified SC polypeptides were subjected to mild periodate oxidation of terminal nonreducing sugars followed by selective reduction with [3H]sodium borohydride, SC polypeptides were further proteolytically cleaved, and the 3H-labeled peptides were isolated and characterized. Both high and low Mr SCs of the three allotypes possess a common glycosylation site at the asparagine residue position 400, whereas the second site, in the amino-terminal domain of SC, was found to be variable: the t61 and t63 allotypes contained a glycosylation site at positions 70 and 90, respectively. Moreover, although the t62 allotype was found to contain a triplet acceptor site (N-X-S) at positions 90-92, analyses showed that less than 30% of the t62 allotype peptides encompassing this region were glycosylated at residue 90. Furthermore, the amino acid sequence of the t61 SC in the region of residues 69-90 varies by 8 and 10 amino acid substitutions when compared with the t62 and t63 allotype sequences, respectively. However, neither the variation in amino acid sequence nor the variation in degree or site of glycosylation measurably affected the non-covalent binding of domain 1 to dimeric IgA.     

The widespread distribution of alpha-N-trimethylalanine as the N-terminal amino acid of light chains from vertebrate striated muscle myosins

Identical tripeptides of the sequence X-Pro-Lys, where X is an unknown blocking group, were isolated from trypsin digests of bovine cardiac alkali light chain and the LC2 light chain of rabbit fast muscle. Chemical, electrophoretic and 1H-NMR evidence characterized X as an unusual amino acid, alpha-N-trimethylalanine (Me3Ala), which was earlier reported as the N-terminal amino acid of the A1 alkali light chain of rabbit fast muscle [Henry et al. (1982) FEBS Lett. 144, 11-15]. The narrow line width and chemical shift position (delta = 3.23 ppm) of the--N+-(CH3) protons of Me3Ala made 1H-NMR spectroscopy a convenient method to search for this residue in other light chains. A survey of many different light chains showed that this signal was present in all vertebrate striated muscle light chains of the A1-type (LC1, 'essential' light chains) and LC2-type ('DTNB'-light chains, 'phosphorylatable' light chains) but was absent from all invertebrate muscle and vertebrate smooth muscle light chains tested. It was also absent from the vertebrate fast-muscle-specific A2-type (LC3) light chains. The spectral characteristics of these signals were consistent with their having arisen from the protons of an--N+-(CH3)3 grouping. Since no epsilon-trimethyllysine could be detected in acid hydrolysates of these proteins, it appears that Me3Ala is a general feature as the N-terminal amino acid in these light chains. 1H-NMR studies on bovine cardiac myosin subfragment 1 (S1) showed that the Me3Ala methyl proton signal was clearly visible and that the spectrum more closely resembled that of a rabbit S1 isoenzyme, S1(A1), than S1(A2), suggesting that the 40-residue N-terminal segment of the alkali light chain in cardiac S1 also possesses a high segmental mobility. Addition of actin caused the same gross changes to the cardiac S1 spectrum as noted earlier for rabbit S1(A1) [Prince et al. (1981) Eur. J. Biochem. 121, 213-219]. In particular, a marked reduction in the segmental mobility of the N-terminal region of the alkali light chain was noted, consistent with a direct interaction of this area with actin.     

Amino acid sequence of the N-terminal 139 residues of light chain derived from a homogeneous rabbit antibody

The amino acid sequence of the N-terminal 139 residues of the L (light) chain derived from a homogeneous rabbit antibody (designated BS-1) to type III pneumococci was determined. A combination of methods involving tryptic cleavage restricted to the 2 arginine residues of the molecule and mild acid hydrolysis of a labile peptide bond between the V (variable) and C (constant) regions of the L chain (Fraser et al., 1972) allowed the isolation of two large peptides comprising the entire V region (residues 1-109); these peptides were suitable for automated Edman degradation. The complete sequence analysis of the V region was carried out with only 4mumol of L chain. This material was homogeneous, although minor variant sequences, if present at the 10% value, would not have been detected. The L chain contains 3 intrachain disulphide bridges, whose pairing was established by diagonal electrophoresis: there is one V-region bridge between positions 23 and 88 and one C-region bridge between positions 134 and 194; the third one connects V and C domains between positions 80 and 171. When compared with the basic sequence of human kappa chains, rabbit L chain BS-1 appears to be more similar to the V(KI) prototype sequence than to V(KII) or V(KIII) sequences, where V(KI), V(KII) and V(KIII) represent subgroups I, II and III respectively of V regions of kappa light chains. The V regions of rabbit heavy and light chains are homologous to each other. The presence of two clusters of 3 glycine residues in positions 94-96 and 99-101 respectively is remarkable. Residues 94-96 may be related to antibody complementarity whereas residues 99-101 function probably as a pivot permitting the combining region of the L chain to make optimal contact with the antigenic determinant (Wu & Kabat, 1970).     

A novel idiotopic determinant on phosphorylcholine-binding immunoglobulins restricted to isotype and allotype

A shared idiotopic (Id) determinant, designated B24-50, was detected on phosphorylcholine (PC)-binding myeloma proteins by using a monoclonal antibody. Analysis of immune sera from inbred and congenic strains of mice revealed the presence of this Id determinant on a very small proportion of the PC-binding immunoglobulins (Ig). Hybridoma and myeloma proteins of various classes were analyzed for B24-50 expression, and a clear association of B24-50 with IgA was demonstrated. The Id was found on two distinct idiotypic families, (TEPC15 and McPC603), which share a similar heavy chain but have different light chains; however, isolated heavy chains did not express B24-50. The Id did not require the absolute association of the TEPC15 light chain V kappa 22 with the TEPC15 heavy chain but appeared dependent upon the interaction of the light chain with the TEPC15 heavy chain via quaternary interactions and/or shared amino acid residues of V kappa 8 (M603) and V kappa 22. Furthermore, B24-50 was not found on IgA of strains with the Ighb allotype. Thus B24-50 is a novel isotype-restricted determinant found on two Id families and is influenced by the Igh allotype.     

The sequences of rabbit kappa light chains of b4 and b5 allotypes differ more in their constant regions than in their 3'' untranslated regions.

We report the sequence of a cDNA clone encoding the entire variable and constant regions of a rabbit kappa light chain of b5 allotype. The deduced amino acid sequence of the variable region (positions 1-95) is 86% homologous to that of a b4 light chain protein [BS-1) (1) but the b4 and b5 constant regions are only 74% homologous. Comparison of this DNA sequence to that of a cDNA clone encoding a b4 constant region shows that the kappa allotypes b4 and b5 have diverged significantly more in their coding region than in the 3' untranslated regions (86% vs 96% nucleotide sequence homologies). This implies either a function for the 3' untranslated region with evolutionary pressures to conserve or an accelerated divergence of the coding regions.     

Sequence studies on the constant region of the Fd sections of rabbit immunoglobulin G of different allotype.

The amino acid sequence has been completed for the constant region of the Fd fragments of heavy chains from rabbit IgG (immunoglobulin G) of allotype Aa1 and Aa3. The amino acid sequence given by Fruchter et al. [(1970) Biochem. J. 116, 249-259] for the constant region of the Fd fragment from Aa1 IgG was extended and in in part corrected to give a continuous sequence of 140 residues. No allotype-related sequence variation was found in the constant section of the Fd fragment. This evidence confirms the view that the differences in sequence between the variable regions of Aa1 and Aa3 IgG [Mole et al., (1971) Biochem. J. 124, 301-318] are responsible for the allotypic specificities.     

RNA conversion of lymphoid cells to synthesize allogeneic immunoglobulins in vivo

Ribonucleic acid extracts (“5 day immune” and “nonimmune”-RNA) obtained from lymph nodes and spleens of rabbits homozygous for the b⁴ or b⁵ allele of light chain immunoglobulin allotypes were injected iv into nonimmunized rabbits homozygous for the alternate allele. The recipient rabbits were then given multiple iv injections of sheep red blood cells (SRBC). The spleens were assayed 13, 21, and 37 days following the RNA injection for “direct” IgM and “indirect” IgG plaque forming cells (PFC) specific for SRBC. The b4 or b5 light chain allotype and the a1, a2, and a3 heavy chain allotype of the antibody in the plaques was identified by radioautography and by inhibition of plaque formation using anti-allotype antibodies. The b light chain allotype of the RNA donor was identified in 22–32% of the IgM plaques and in 25–42% of the IgG plaques. The allotype of the host rabbit b light chain allotype was identified in 56–67% of the IgM plaques and in 57–71% of the IgG plaques. Likewise the a heavy chain allotype of the RNA donor was identified in 10–19% of the IgM plaques and in 12–19% of the IgG plaques. The allotype of the host rabbit a heavy chain allotype was identified in 51–60% of the IgM plaques and in 55–63% of the IgG plaques. The concentrated lysates of spleen and lymph node cells were also analyzed for immunoglobulins of each light chain allotype by immunodiffusion with radiolabeled antibody. The allotype of both the RNA donor rabbit and host rabbit were found in most of the lysates of lymphoid tissues and in some of the IgG isolated from the serum and concentrated.