Complete amino acid sequence of the Mu heavy chain of a human IgM immunoglobulin

The amino acid sequence and gene organization of the heavy chain of the HLA-DR antigen: homology to immunoglobulins

The amino acid sequence of the heavy chain of HLA-DR antigens has been elucidated from the analysis of a genomic clone coding for this protein. A 3.2-kilobase EcoRI fragment includes four exons containing 227 amino acids out of 229 in the mature HLA-DR heavy chain. One exon (alpha 2) encodes a domain of 94 amino acids with strong sequence homology both to Ig constant region domains and to Ig-like domains in HLA-B7, beta 2-microglobulin, and the HLA-DR light chain. These results support a structure for the HLA-DR antigen heterodimer consisting of four extracellular domains, two of which are Ig-like [one in the heavy chain (alpha 2) and one in the light chain (beta 2)]. The third is the amino-terminal polymorphic domain in the light chain (beta 1), and the fourth is an invariant domain in the heavy chain (alpha 1).

Neuronal cell Thy-1 glycoprotein: homology with immunoglobulin

The amino acid sequences of mouse brain Thy-1 glycoproteins are shown to be homologous to those of variable-region immunoglobulin domains. There is also good homology with constant domains and beta 2-microglobulin; overall the results suggest that Thy-1 may be like the primordial immunoglobulin domain. Preliminary evidence for an invertebrate Thy-1 homolog supports this possibility.

Complete amino acid sequence of the delta heavy chain of human immunoglobulin D

We have determined the amino acid sequence of the variable (V) region of the delta heavy (H) chain of human IgD isolated from the plasma of myeloma patient WAH. This V region is unusual in its amino end group (arginine) and in its length (129 residues). The length is due to 10 insertions in the third complementarity-determining region (CDR3). A computer search showed that no reported CDR3-joining region (-JH) sequences are identical and that they appear to be unrelated to the constant (C) region sequences of immunoglobulins. The V region sequence together with our previous results for the C region give the complete sequence of the human delta chain WAH, which has 512 amino acid residues and a Mr congruent to 65,000. The human delta chain has four domains (V, C delta 1, C delta 2, and C delta 3) and a long hinge region; by comparison, the mouse delta chain lacks a continuous segment of 135 residues, including half the hinge region and the entire C delta 2 domain. The human and mouse delta chains also differ in the number, kind, and location of GlcN and GalN glycans and probably in conformation and quaternary structure. These and other considerations suggest that there may be multiple forms of both secreted and membrane-bound IgD that differ in size, structure, and function.

The predominant surface glycoproteins of thymocytes and lymphocytes

The surfaces of thymocytes and T and B lymphocytes differ markedly in their predominant glycoprotein constituents. Amino acid sequence studies show that a surprising number of the cell surface molecules have homologies with immunoglobulins. Analysis of carbohydrate shows major differences between glycoproteins on the same cell and between the same (or closely related) glycoproteins on the different cell types.

Structural differences between heavy chains of secreted and membrane-bound IgM of a human lymphoblastoid cell line

The human lymphoblastoid cell line BL was shown to synthesise three distinct molecular species of immunoglobulin M heavy chains: membrane-bound (micrometer). intracellular (micro i) and secreted (microseconds) micro-chains. Only the membrane-bound form could be labeled with a lipophilic photoactivatable nitrene reagent. Analysis of their constituent CNBr fragments and carboxypeptidase A and B digestions of their C-terminal tails suggest that the CNBr peptide pattern of microseconds and micrometer, though similar, is not identical, and that amino acids released at the C-termini of the chains are different. The data confirm recent observations in human and murine systems be showing that the membranes-associated human micro-chain contains a hydrophobic segment, consistent with its anchorage into the lipid bilayer of the plasma membrane and a C-terminal amino acid sequence different from that of the secretory micro-chain.

Amino acid sequence of the first constant region domain and the hinge region of the delta heavy chain of human IgD

We have determined the amino acid sequence of the first constant (C) region domain (C delta 1) and the hinge region of the delta heavy chain of human IgD WAH and also the sequence of the adjacent COOH-terminal portion of the variable (V) region, including the JH region. Together with the sequence of the Fc fragment already reported, this establishes the complete amino acid sequence of the C region of the human delta chain and confirms the presence of three C region domains in human IgD. Although the CH1 domains of the five classes of human heavy chains have the expected degree of homology (approximately 30%), the homology of the C delta 1 domains of the human and mouse chains is less than that exhibited by the CH1 domains of other pairs of human and mouse heavy chains. The hinge region of the human delta chain has an unusual structure; the NH2-terminal half has four (or five) GalN oligosaccharides attached, whereas the COOH-terminal half lacks carbohydrate, is dissimilar in sequence, and has a high charge. A computer search verified that the GalN-rich segment has a high degree of identity in sequence with the middle portion of the human C mu 2 domain and that the high-charge segment is related to the same sequence. We propose that the two segments of the human delta hinge have a common evolutionary origin and arose by duplication and independent mutation of a hinge exon derived from the ancestral gene for the C mu 2 domain.

A comparison of the actions of trypsin and pepsin on porcine immunoglobulin M and their effects on biological activity

The action of trypsin at 55 degree C and pH 8.3 on pig IgM anti-Salmonella has been compared with the action of pepsin at 37 degree C and pH 4.6. Both processes cause the gradual removal of Fab arms and Cmu2 domains to produce eventually an (Fc)5 fragment. However, during tryptic digestion Fab arms are preferentially removed from the same subunit, whereas peptic digestion causes random removal from any subunit. At intermediate stages of digestion both processes produce partially fragmented molecules which consist of an (Fc)5 portion still attached to limited numbers of Fab arms. Both processes cause a gradual decrease in the ability of molecules to agglutinate Salmonella, but complement fixation by the complexes declines much more rapidly. A stage is reached where molecules having four Fab arms can still agglutinate but there is no complement fixation. However, the remaining arms on the tryptic molecules are distributed in pairs on the same subunit, whereas those on the peptic molecules are distributed randomly. Hence the number of remaining Fab arms, rather than their distribution, appears to be the critical factor which influences biological activity. A possible explanation for this is discussed.

Localization and overall structure of a mannose-rich glycopeptide from a pathologic immunoglobulin

The structure of a mannose-rich glycopeptide from a human pathological IgM has been investigated. It belongs to the group I (simple) glycopeptides and contains only mannose and N-acetylglucosamine residues in a molar ratio of 10:2. The structures of its oligosaccharide moiety and peptide chain have been determined: its molecular localization is specified and the relation between its biosynthesis and the oligosaccharide structure determine is discussed. Based on the alpha- and beta-mannosidase digestions and permethylation studies for the oligosaccharide moiety, and on the results obtained after sequential analysis of the peptide chain, the following structure is proposed for the mannose-rich IgM Du glycopeptide: (Formula: see text). The recovery of one molecule of this glycopeptide per molecule of heavy chain and the determination of the amino acid sequence have led us to locate this glycopeptide on asparagine 402 of the Fc portion of the heavy chain mu of IgM Du.

Complete amino acid sequence of the Fc region of a human delta chain

The complete amino acid sequence of an Fc-like fragment designated Fc delta (t) and obtained by limited proteolysis with trypsin of an intact myeloma IgD protein (NIG-65) has been determined. The fragment contains 226 amino acid residues and has a molecular weight of 32,000 per monomeric unit. It has three glucosamine oligosaccharides at asparagine residues 68, 159, and 210. Of these, glucosamine-159 is characteristic of the delta chain and has no counterpart position in any of the other classes. On the other hand, glucosamine-68 is shared by gamma, mu, and epsilon, and glucosamine-210 is shared by alpha and mu. Although the Fc delta (t) has the common framework structure of immunoglobulins, its sequence has many individual characteristics when its two domains are compared separately with the counterpart domain of other heavy chains. Such comparison has shown that the two Fc domains of the delta chain should be placed in an independent branch in topology; for all the other classes, the Fc domains are paired well with their counterparts. The comparison has also shown that there are three prominent gaps by which each domain can be divided into two homologous halves. For each class of immunoglobulin, a moderate degree of internal homology exists between the first half and the second half of each domain of the Fc, suggesting that the primordial gene may have coded for a unit about the size of a half domain. Based on this observation together with sequence comparisons, a possible genetic mechanism is proposed for the origin and evolution of the genes for immunoglobulin domains.

Primary structure of the Fc region of human immunoglobulin D: implications for evolutionary origin and biological function

We have determined the complete amino acid sequence of a tryptic Fc delta fragment generated from an intact human IgD (WAH); it is 226 residues long and includes the second (C delta 2) and the third (C delta 3) constant domains of the delta chain. Comparison of the homology of the Fc sequence of the five human immunoglobulin classes suggests that either the delta-chain gene evolved from the alpha-chain gene soon after the divergence of a mu-alpha common ancestor or it evolved from an ancestral gene distinct from both the mu-alpha and the gamma-epsilon common ancestors. Comparative study using a spatial model of the Fc region indicates that the structure of the C delta 3 domain differs extensively from that of the carboxy-terminal domains of other heavy chain classes; this, together with the unique hinge region structure, probably reflects the biological role of IgD as a receptor molecule on the B-lymphocyte surface.

Cloning of human immunoglobulin mu gene and comparison with mouse mu gene

We have cloned a 12 kb DNA segment containing human mu gene and its flanking sequence from human fetal liver DNA library using mouse mu gene as a probe. Partial nucleotide sequence determination shows that the cloned DNA contains the sequence encoding human mu chain. This is the first constant region gene of the human heavy chain that is cloned. We have compared human and mouse mu genes by heteroduplex analysis and Southern blot hybridization. The results clearly show that not only the sequence encoding the CH4 domain but also the 5'-flanking (S mu) sequence is conserved between human and mouse mu genes, suggesting that the nucleotide sequence in the S mu region has an important biological function, presumably a recognition signal for the class switch recombinant as proposed previously.

The primary structure of the constant part of mu-chain-disease protein BOT

The complete primary structure of the constant part of the mu-chain-disease protein, BOT, was established. It includes the whole CH2, CH3 and CH4 domains. two amino acid changes were found, at positions 309 (Ser leads to Gly) and 333 (Val leads to Gly) (GAL numbering). In two additional monoclonal mu chains (SCO and CO), the same positions showed an amino acid variability. From these data it may be concluded that four types of mu chains exist in the human: (1) GAL type with Ser-309 and Val-333; (2) OU type with Gly-309 and Val-333; (3) SCO type with Ser-309 and Gly-333; (4) BOT/CO type with Gly-309 and Gly-333. The meaning of this molecular polymorphism is discussed.

Cloning and partial nucleotide sequence of human immunoglobulin mu chain cDNA from B cells and mouse-human hybridomas

Purified mRNAs coding for mu and kappa human immunoglobulin polypeptides were translated in vitro and their products were characterized. The mu-specific mRNAs, derived from both human lymphoblastoid cells (GM607) and from a mouse-human somatic cell hybrid secreting human mu chains (alpha D5-H11-BC11), were copied into cDNAs and inserted into the plasmid pBR322. Several recombinant cDNAs that were obtained were identified by a combination of colony hybridization with labeled probes, in vitro translation of plasmid-selected mu mRNAs, and DNA nucleotide sequence determination. One recombinant DNA, for which the sequence has been partially determined, contains the codons for part of the C3 constant region domain through the carboxy-terminal piece (155 amino acids total) as well as the entire 3' noncoding sequence up to the poly(A) site of the human mu mRNA. The sequence A-A-U-A-A occurs 12 nucleotides prior to the poly(A) addition site in the human mu mRNA. Considerable sequence homology is observed in the mouse and human mu mRNA 3' coding and noncoding sequences.

The action of pepsin on porcine immunoglobulin M and its effect on biological activity

Treatment of porcine immunoglobulin M (IgM) with pepsin at pH 4.6 and 37 degrees C was found to gradually remove Fab arms and Cmicro2 domains over a period of 18h. Structural studies failed to find any other change. The main products can therefore be regarded as IgM-like molecules with limited numbers of Fab arms and Cmicro2 domains. Results indicated that this removal of Fab arms is probably a random process. As the average number of Fab arms per molecule was decreased the ability to agglutinate Salmonella oranienburg (mt-H) gradually diminished. Complement fixation by the complexes however, decreased rapidly, and became negligible when the average number of Fab arms was four. This was confirmed by using a preparation containing mainly molecules with three or four Fab arms. The overall results showed that molecules with three or four Fab arms can agglutinate Salmonella but that these complexes do not fix complement. Molecules with five arms probably behave like those with four. Complexes formed by molecules with six arms fix complement quite efficiently. Possible explanations for these results are discussed.

Complete nucleotide sequence of mouse immunoglobulin mu gene and comparison with other immunoglobulin heavy chain genes

We have determined the complete nucleotides sequence (2168 bases) of the immunoglobulin mu gene cloned from newborn mouse DNA. The cloned 13kb fragment contained the entire constant region gene sequence that is interrupted by three intervening sequences at the junction of domains as previously shown in the gamma 1, gamma 2 b and alpha genes. The amino acid sequence predicted by the nucleotide sequence agrees with that of the mu chain secreted by a myeloma MOPC104E except for 8 residues out of 448 residues. The homologous domains of the mu, gamma 1 and gamma 2b genes are more similar to each other than the different domains of the mu genes are. The result implicates that the class of the immunoglobulin heavy chain genes diverged after the heavy chain genes established the multi-domain structure. The short intervening sequences of the mu and gamma genes are more conserved than the coding sequences except for the COOH-terminal domains. The results implicate that the nucleotide sequence of the intervening sequence is under selective pressure, possibly to maintain a secondary structure of the nuclear RNA to be spliced.

Linkage and sequence analysis of mannose-rich glycoprotein core oligosaccharides by proton nuclear magnetic resonance spectroscopy

The anomeric proton (H-1) chemical shifts of D-mannopyranosides in aqueous solution are affected both by the aglycon and by substitution of the ring [Lee, Y. C., & Ballou, C. E. (1965) Biochemistry 4, 257]. We have examined the 1H NMR spectra for a variety of linear and branched mannooligosaccharides and have assigned the H-1 resonances to the component sugars. The chemical shifts, which range from delta 4.76 to 5.36, provide information regarding the linkages, sequences, and anomeric configurations of mannose residues in an oligomer. Thus, 1H NMR spectroscopy can complement enzymatic hydrolysis, methylation analysis, and acetolysis for the structural characterization of oligosaccharides. Furthermore, small structural differences between otherwise identical oligosaccharides are often accompanied by long-range chemical shift changes for the anomeric protons. Because sugars three or more residues away from the structural alteration can be affected, the changes must reflect conformational differences. We have placed emphasis on the mannose-rich oligosaccharides from glycoproteins, particularly those produced by endo-beta-N-acetylglucosaminidase digestion. Two mannose-rich glycopeptides were isolated from a monoclonal human IgM and their positions of origin on the polypeptide chain were determined. The oligosaccharides were released with endo-beta-N-acetylglucosaminidase and fractionated into several size classes. Our structural studies show that each glycopeptide possessed a unique set of oligosaccharides, in agreement with a recent report [Chapman, A. & Kornfeld, R. (1979) J. Biol. Chem. 254, 816]. The NMR spectra were particularly valuable in detecting and quantitating isomeric fragments not observed previously, and our results suggest a modification of the scheme presented by Chapman and Kornfeld for the processing of mannose-rich IgM oligosaccharides.

Biogenesis of membrane-bound and secreted immunoglobulins. I. Two distinct translation products of human mu-chain, with identical N-termini and different C-termini

Structural differences between the heavy chain of membrane-bound IgM (mu m) and the heavy chain of secreted IgM (mu s) were investigated. The primary translation products of the mu-chain, free of posttranslational modifications, were synthesized in a wheat-germ cell-free system, programmed with messenger RNA derived from human lymphoblastoid cell lines positive for both membrane-bound and secreted IgM. Encoded in this sytem were two mu-chains, which shared N-terminal signal peptides and which differed both in molecular weight and in C-terminal amino acid sequence. In vivo pulse labeling of cells confirmed that, as intermediates in the rough endoplasmic reticulum, these two forms expressed the same idiotype and maintained their difference in molecular weight and in C-terminal sequence. By correlation with pulse-chase kinetics and with immunofluorescence, one form of mu-chain represents mu m, and the other, mu s. Because the molecular weight difference between the two is manifest at the level of their primary translation products, these studies demonstrate that mu m is distinguished from mu s by a difference in primary structure, at least in part at the C-terminus.

Amino acid sequence of the variable region of a human mu chain: location of a possible JH segment

The complete amino acid sequence of th variable (V) region of the mu heavy chain of a human IgM immunoglobulin (Cam) has been determined. The strategy for sequence determination involved sequenator analysis of the CNBr cleavage products of the succinylated carboxymethylated Fab mu fragment, and of tryptic peptides of the CNBr polypeptides and thermolytic subpeptides. The variable region of this heavy chain (VH) belongs to the VHIII subgroup; it has greater than 70% homology with other VHIII sequences and contains the VHIII marker peptide, Phe-Thr-Ile-Ser-Arg (residues 67-71). As more sequences have been published, the number of subgroup-specific residues has diminished to the point that no position is absolutely subgroup specific. An analysis of the available human VH sequences in the V/C switch region showed the likelihood of a human JH segment (residues 101-113) analogous to the J segments in mouse light chains. The JH region is highly conserved, has striking homology to proposed mouse JH regions, and has significant homology to known mouse J lambda and J kappa segments.

Different species of messenger RNA encode receptor and secretory IgM mu chains differing at their carboxy termini

Biosynthetic studies in the presence of an inhibitor of glycosylation indicate that individual human lymphoma-derived cell lines can synthesize both membrne receptor and presumptive secretory forms of IgM mu chains. The receptor form has a larger polypeptide chain than the secretory form and possesses a different C-terminus, but similar N-terminus, consistent with the presence of a C-terminal hydrophobic "tail" for integral membrane binding. Messenger RNA isolated from these cells directs the synthesis of both forms of mu chains in a wheat germ translation system, indicating the presence of independent mRNAs for each form. It is proposed that the synthetic pathways for receptor and secretory IgM diverge at the post-transcriptional level, possibly by differential RNA splicing to give mRNA molecules with or without a translatable "tail" segment.

Origins of immunoglobulin heavy chain domains

Using computer programs that analyze the evolutionary history and probability of relationship of protein sequences, we have investigated the gene duplication events that led to the present configuration of immunoglobulin C regions, with particular attention to the origins of the homology regions (domains) of the heavy chains. We conclude that all of the sequenced heavy chains share a common ancestor consisting of four domains and that the two shorter heavy chains, alpha and gamma, have independently lost most of the second domain. These conclusions allow us to align corresponding regions of these sequences for the purpose of deriving evolutionary trees. Three independent internal gene duplications are postulated to explain the observed pattern of relationships among the four domains: first a duplication of the ancestral single domain C region, followed by independent duplications of the resulting first and last domains. In these studies there was no evidence of crossing-over and recombination between ancestral chains of different classes; however, certain types of recombinations would not be detectable from the available sequence data.

Mouse Cmu heavy chain immunoglobulin gene segment contains three intervening sequences separating domains

The IgM molecule is composed of subunits made up of two light chain and two heavy chain (mu) polypeptides. The mu chain is encoded by several gene segments--variable (V), joining (J) and constant (Cmu). The Cmu gene segment is of particular interest for several reasons. First, the mu chain must exist in two very different environments--as an integral membrane protein in receptor IgM molecules (micrometer) and as soluble serum protein in IgM molecules into the blood (mus). Second, the Cmu region in mus is composed of four homology units or domains (Cmu1, Cmu2, Cmu3 and Cmu4) of approximately 110 amino acid residues plus a C-terminal tail of 19 residues. We asked two questions concerning the organisation of the Cmu gene segment. (1) Are the homology units separated by intervening DNA sequences as has been reported for alpha (ref. 5), gamma 1 (ref. 6) and gamma 2b (ref. 7) heavy chain genes? (2) Is the C-terminal tail separated from the Cmu4 domain by an intervening DNA sequence? If so, DNA rearrangements or RNA splicing could generate hydrophilic and hydrophobic C-terminal tails for the mus and micrometer polypeptides, respectively. We demonstrate here that intervening DNA sequences separate each of the four coding regions for Cmu domains, and that the coding regions for the Cmu4 domains and the C-terminal tail are directly contiguous.

Lactoperoxidase-catalyzed iodination of human IgM. Differences between 7 S IgM and 19 S IgM and between cell surface 7 S IgM and serum 7 S IgM

We have studied the lactoperoxidase-catalyzed iodination of human IgM and have measured the ratio of radioactivity incorporated into the mu chain to that incorporated into the L chain (i.e. the mu/L ratio). Both 7 S and 19 S IgM were examined. The ratio of radioactivity was found to be larger for 7 S IgM than for 19 S IgM for all four of the monoclonal IgM proteins examined. The data suggest that some tyrosines of the mu chain which are buried and not available for iodination in 19 S IgM become exposed on conversion of 19 S IgM to 7 S IgM. The mu/L ratio for the IgM found on the cell surface of RPMI 8392 cells was significantly smaller than the ratios for all of the five 7 S IgM proteins studied in solution. It appears, therefore, that a portion of the mu chain of the cell surface IgM of the RPMI 8392 cells is buried in the membrane.

Mouse intracellular immunoglobulin M. Structure and identification of a free thiol group

Monomeric intracellular mouse immunoglobulin M (hereafter designated IgMs) was purified in milligram quantities from the plasma cells of mouse plasmacytoma MOPC 104E after lysis either in the presence or in the absence of iodoacetate. Peptide ;mapping' analysis of the IgMs after partial reduction and carboxy[(14)C]methylation to label the interchain disulphide bridges showed that the heavy-light bridge and the interheavy bridge present in the Cmu2 region were already formed at lysis. The cysteine residues in the C-terminal region of the heavy chains, which in pentameric IgM form an intersubunit bridge, had free thiol groups at lysis that were reversibly oxidized during isolation in the absence of iodoacetate, probably forming an intrasubunit inter-heavy-chain disulphide bridge. Isoelectric-focusing studies complemented the above findings, showing that all the intracellular IgMs carried free thiol groups that could be carboxymethylated at lysis, and that in non-alkylated preparations these had reversibly oxidized. On the basis of sodium dodecyl sulphate/polyacrylamide-slab-gel electrophoresis intracellular mu-chains had a consistently lower apparent molecular weight than did secreted mu-chains, and the estimated difference could be accounted for by the known difference in carbohydrate content. We present evidence that in a position homologous to that of a complex oligosaccharide in the Cmu2 region of secreted human mu-chains there is a simple oligosaccharide in intracellular mouse mu-chains that becomes complex on secretion. On the basis of the above findings, we present a model for the mouse intracellular IgM subunit and suggest a mechanism for its assembly into secreted IgM pentamers.

Genetic determination of antibody specificity. Gene translocation and fusion, the molecular basis for the differentiation of the antibody-producing cell

The best system for the study of cell differentiation is a cell which in its differentiated state differs only by one product. This is the case in the immune system. The undifferentiated, but omnipotent stem cell differentiates into a committed B cell which produces only one type of specific antibody out of a million different, genetically fixed possibilities. Gene translocation and fusion is the basis of this differentiation process.