Homogenous IgA monomers, dimers, trimers and tetramers from the same IgA myeloma serum

Starting from two IgA1 myeloma sera, the isolation of monoclonal monomeric, dimeric, trimeric and tetrameric IgA in a high state of purity and size homogeneity for each serum is described. The method combined repetitive gel filtrations on Ultrogel AcA22 with affinity chromatography on Jacalin-Sepharose. These various forms of pure polymeric IgA obtained from the same monoclonal IgA should allow a precise comparison of their respective structure and reactivity with different IgA-binding proteins, such as IgA Fc-receptors, the polymeric Ig receptor, and lectins.

The amino acid sequence of rabbit J chain in secretory immunoglobulin A

The primary structure of rabbit J chain, which occurs covalently bound to secretory IgA, was determined. J chain was isolated in its S-carboxymethylated form, in one step, by SDS/PAGE followed by electro-elution; 5 nmol of protein (approx. 75 micrograms), in all, was necessary for the determination of the complete sequence by the 'shot-gun' microsquencing technique; with the use of several site-specific endoproteinases, the various digests of S-carboxymethylated J chain were separated by micro-bore reverse-phase h.p.l.c. and the partial N-terminal sequences of all peptides were analysed. From the sequence alignment, gaps were filled by further extensive sequencing of the relevant overlapping fragments isolated from selected digests. Rabbit J chain comprises 136 amino acid residues, out of which eight are conserved cysteine residues, and is more closely similar to the human sequence (73.5% identify) than to the mouse sequence (68% identity). There is one unique glycosylation site at asparagine-48.

Identification of mouse J chain in human IgM produced by an electrofusion-derived mouse-human heterohybridoma

EBV transformed human B cell line secreting IgM was fused with X63-Ag8.653 mouse cell line. Hybrids were selected in medium containing HAT and ouabain. IgM from a clone was purified by affinity chromatography. Western blot analysis of the heterohybridoma IgM showed the presence of mouse J chain when probed with antiserum against mouse J chain.

J chain in Rana catesbeiana high molecular weight Ig

A polypeptide homologous to human and mouse J chain has been identified in the high molecular weight (HMW) Ig of the bullfrog, Rana catesbeiana. In previous studies, we had detected a component that was similar in size to mammalian J chains and that, relative to L chains, migrated rapidly to the anode in alkaline-urea PAGE; however, its mobility was less than that of mammalian J chains. We now demonstrate that this component is covalently linked to the H chain of R. catesbeiana HMW Ig. All of the disulfide bridges of this polypeptide, like those of human and mouse J chain, can be cleaved by reducing agents even in the absence of denaturing solvents. The putative frog J chain was isolated by a procedure that did not require preliminary purification of the HMW Ig. The chain differed in amino acid composition from L chains but resembled J chains from several other species. Tryptic peptides were isolated and sequenced. Except for a single heptapeptide, the peptides could be aligned by virtue of their similarity to segments of human and mouse J chain. Of the 116 residues that were placed, 55 were identical with residues in human J chain and 60 with residues in mouse J chain. The six cysteine residues identified in the frog J chain are at the same positions as six of the eight cysteines in the human and mouse J chains. The results indicate significant conservation in structure between amphibian and mammalian Ig J chains.

Overproduction of immunoglobulin mRNA by a murine myeloma MOPC 315 variant cell line

The mouse myeloma MOPC 315 cell line synthesizes and secretes IgA (lambda 2) immunoglobulin. A spontaneously arising variant of the MOPC 315 line, which had been isolated as apparently oversecreting IgA protein, has been characterized. The variant line has been shown to synthesize and secrete increased levels of heavy chain, light chain, and J chain polypeptide compared to the parental wild-type cells from which it was isolated. The steady-state levels of cytoplasmic mRNA for these polypeptides are increased commensurately in the over-producing line. For the heavy chain, enhanced transcription, and possibly increased gene dosage, appear to be involved. The increased levels of the three individual immunoglobulin polypeptide chains suggest that the variant line displays a coordinate regulation of expression of immunoglobulin genes.

Amino- and carboxy-terminal sequence of mouse J chain and analysis of tryptic peptides

Mouse J chain was isolated from an IgM-producing hybridoma by gel filtration and ion-exchange chromatography. The sequence of the amino-terminal 25 residues was determined. At these positions, the results agree with the amino acid sequence deduced from the cDNA sequence determined previously by Koshland and co-workers and indicate that a leader sequence terminating in glycine is removed to form the mature J chain. Tryptic peptides of J chain were isolated by high pressure liquid chromatography and their amino acid compositions were compared with those expected from the cDNA sequence. The amino acid sequence of the carboxy-terminal peptide and a mixture of two other peptides was determined. The results were consistent with the cDNA sequence except that we found valine, not leucine, at position 67, and arginine, not glycine, at position 117. The presence of aspartic acid at the carboxy-terminus, as predicted from the cDNA, indicates that processing does not occur at this end of the polypeptide chain. Upon amino acid analysis, glucosamine was found in tryptic peptides 47-57 and 47-58. J chain was also cleaved at aspartylproline bonds with formic acid and the unfractionated digest was subjected to automated Edman degradation. The mixed sequence was consistent with the sequence deduced from the cDNA at positions 1 to 13, 28 to 40, 52 to 64, and 73 to 85. In conjunction with the results obtained previously by analysis of cDNA, these data show that mouse J chain is a polypeptide containing 137 amino acid residues, 93 of which are identical to residues in human J chain.

Xenopus laevis 19S immunoglobulin. Ultrastructure and J chain isolation

Electron microscopy examination of the 19S immunoglobulin of Xenopus laevis revealed a hexameric structure with a central core. The molecules measured 360-430 A across the span of the arms and the average diameter of the central region was 140 A. A polypeptide, homologous to human J chain, was isolated by chromatography on DEAE-cellulose from the reduced and alkylated X. laevis hexameric macroglobulin. This polypeptide had a fast mobility in alkaline-urea gel electrophoresis, with distinct antigenicity, as compared to heavy and light chains. It shared common antigenic determinants with human J chain.

Synthesis but not secretion of J chain by variant mouse myeloma cells which lose alpha-chain-synthesizing ability

We have devised a rapid method for obtaining large amounts of J chain from IgA in the ascitic fluid of mice bearing the MOPC 315 tumor. The J chain was released by reduction from the MOPC 315 IgA adsorbed onto a DNP-lysyl-Sepharose column, and was further purified by DEAE Sephadex chromatography. The mouse J chain was characterized as to its electrophoretic mobility, amino acid composition, apparent size, presence in different immunoglobulin classes, and reactivity with an antiserum containing anti-J chain activity. Variant cell lines have been selected from the IgA-producing mouse myeloma cell line MOPC 315. The variants did not synthesize detectable quantities of alpha heavy chains but continued to synthesize and secrete light chains. J chain was synthesized by both parent and variant cell lines but only secreted by the parent cells. It is postulated that J chain synthesis is not dependent on alpha heavy chain synthesis, but that secretion of J chain by MOPC 315 cells occurs only because of its attachment to the Ig1 molecule.

Identification and properties of J chain isolated from catfish macroglobulin

After the cleavage of disulfide bonds of macroglobulin isolated from channel catfish (Ictalurus punctatus), an electrophoretically fast-moving polypeptide, which resembled human J chain, was released. On a Sephadex G-200 column equilibrated in 5 M guanidine, the elution position of the J chain overlapped with the descending part of the L chain peak. Further purification was achieved by DEAE ion-exchange chromatography. The isolated polypeptide, which had a molecular weight of 14,800 +/- 500, as determined ultracentrifugally by sedimentation equilibrium in 5 M guanidine, contained 7% carbohydrate with one residue of fucose, two of mannose, one of galactose, two of glucosamine, and one of sialic acid per chain. A comparison of catfish and human J chain amino acid analyses showed the former to have a higher content of serine, glycine, and phenylalanine and a lower content of aspartic acid, isoleucine, and arginine. Tryptic peptide maps of catfish and human J chains revealed very few common peptides. Rabbit and guinea pig antisera to human J chain did not cross-react with catfish J chain. Untreated, resuced and alkylated, S-sulfonated, or cyanogen bromide cleaved macroglobulin from the gar (Lepisosteus osseus) contained no polypeptide analogous to either catfish or human J chain by the criteria employed in this study.

Purification of J chain after mild reduction of human immunoglobulins

Two methods are described for the purification of J chain from polymeric IgA after mild reduction without the use of alkylating or dissociating reagents. The released peptide was separated from other protein components by immunoadsorption combined with gel filtration or anionic-exchange chromatography, or both. J chain was thus obtained in a yield of about 30% of the total release. Most of it consisted of dimers (molecular weight, approximately 25,000 to 30,000) or larger polymers, but re-reduction and alkylation produced a quite homogeneous fraction that sedimented slightly more slowly than egg-white lysozyme. The purity was high enough for successful immunization. When J chain coupled to bovine serum albumin was used as an antigen, all of five rabbits showed a good immune response. Although the same principle could be used for the purification of J chain from IgM and colostral IgA, high purity was more difficult to achieve and the yield was much lower. These preparations contained an unidentified slow-moving component, and the J chain was more prone to become rapidly degraded to smaller fragments.

Site of J chain attachment to human polymeric IgA

A fragment containing J chain was released from human polymeric myeloma IgA protein by cyanogen bromide cleavage. The identity of the fragment was determined by its electrophoretic mobility and antigenic determinants. After purification by gel filtrations and DEAE-Sephadex chromatography, this fraction appeared similar (with respect to its amino acid and carbohydrate compositions and its peptide maps) to the J chain isolated from this IgA protein; the molecular weight was 17,000 +/- 100. Upon reduction and alkylation, with subsequent separation of peptides by gel filtration, three components were obtained: the largest component (molecular weight 13,400) corresponded to the N-terminal segment of J chain and contained a homoserine residue, the second corresponded to the C-terminal part of J chain with 13-18 amino acid residues, and the third corresponded to the C-terminal octapeptide of the alpha chain. The data indicate that J chain is attached to alpha chain(s) through the penultimate cysteine residue of the C-terminal octapeptide.

Investigations of the structural function of the J chain in human immunoglobulin M

Human IgM molecules were treated with Na(2)SO(3) or mercaptoethylamine in concentrations ranging from 2 to 14mm or 2 to 22mm respectively. The dissociation of IgM to IgM(s) varied from 0% to 100%. At the intermediate concentrations of either reagent the amount of freed J chains was less than expected. In an attempt to find an explanation for this, IgM was partially dissociated to IgM(s) with mercaptoethylamine. The IgM(s) isolated by gel filtration was divided according to the ascending and descending portions of the elution curve. These portions were treated with 24mm-mercaptoethylamine and analysed for the presence of J chains. Only the ascending portion contained free J chains. Thus, after mild reduction where not all the IgM molecules are dissociated to IgM(s), some J chains remain covalently attached to some IgM(s) molecules although most of the J chains are freed. It was concluded that the J chain could serve as a ;hitch' for IgM(s) molecules forming intact IgM.