Primary structure of murine major histocompatibility complex alloantigens: isolation, biochemical characterization, and preliminary alignment of CNBr fragments from the H-2Ib glycoprotein

Unusual association of beta 2-microglobulin with certain class I heavy chains of the murine major histocompatibility complex

Class I products of the major histocompatibility complex (MHC) comprise a heavy chain of about 45 kDa noncovalently linked to a 12-kDa beta 2-microglobulin (beta 2m) light chain encoded on a different chromosome. We find that class I products of some mouse strains include an additional 62-kDa molecule which on the following evidence consists of a heavy chain linked covalently with beta 2m. Production of the 62-kDa protein invariably accorded with the occurrence of cysteine at position 121 of the heavy chain (Kb,Kbm1,Kbm3,Dd, and Ld). Substitution of arginine at position 121 invariably accorded with absence of the 62-kDa protein (Kbm6,Kbm7,Kbm9,Kd, and Db). On the basis of observed production versus nonproduction of the 62-kDa molecule, predictions are made regarding residue 121 in class I products for which this is not yet known; namely, Kk, Ks, and Dk, which produce the 62-kDa molecule, as compared with Kj, Qa-2, and TL, which do not. Reported differences in immunologic reactivity between Kb mutant strains with Arg-121 in place of Cys-121 imply that the occurrence of 62-kDa class I products in mice of Cys-121 genotype has functional consequences.

Respiratory syncytial virus envelope glycoprotein (G) has a novel structure

Amino acid sequence of human respiratory syncytial virus envelope glycoprotein (G) was deduced from the DNA sequence of a recombinant plasmid and confirmed by limited amino acid microsequencing of purified 90K G protein. The calculated molecular mass of the protein encoded by the only long open reading frame of 298 amino acids was 32,588 daltons and was somewhat smaller than the 36K polypeptide translated in vitro from mRNA selected by this plasmid. Inspection of the sequence revealed a single hydrophobic domain of 23 amino acids capable of membrane insertion at 41 residues from the N-terminus. There was no N-terminal signal sequence and the hydrophilic N-terminal 20 residues probably represent the cytoplasmic tail of the protein. The N-terminally oriented membrane insertion was somewhat analogous to paramyxovirus hemagglutinin-neuraminidase (HN) and influenza neuraminidase (NA). The protein was moderately hydrophilic and rich in hydroxy-amino acids. It was both N- and O-glycosylated with the latter contributing significantly to the net molecular mass 90K.

Biochemical studies of H-2K antigens from a group of related mutants. I. Identification of a shared mutation in B6-H-2bm5 and B6-H-2bm16

Structural studies of the H-2 gene products from a group of five closely related but independent C57BL/6H-2 mutant mice were undertaken. Each of the mutants exhibits reciprocal graft rejection with the parent. The group is remarkable, however, because each member of this group can accept skin grafts from any other member. The results of biochemical analysis of the H-2 glycoproteins from two of these related mutants, bm5 and bm16, are presented in this report. Evidence is given that the H-2K molecules from these two mutants are identical to each other based on comparative tryptic peptide mapping profiles with the parent. From partial amino acid sequence analysis, K products of both mutants have at least one common difference from the parental type located at residue number 116. Definitive studies established that in both bm5 and bm16 a tyrosine found in the parent molecule is substituted with a phenylalanine in the mutant. These results show that a biochemical difference between the K products of the two mutants and of the parent can be detected, that the mutants appear to be identical with one another even though they arose independently, and that they differ from the other H-2Kb mutants analyzed.

Biochemical studies on the H-2K mutant B6.C-H-2bm10

The H-2K glycoprotein from the MHC mutant bm10 was analyzed biochemically to determine where primary structural differences distinguished it from the parental standard molecule, Kb. Comparative peptide maps showed differences in two peptides known to be part of the parental CNBr fragment spanning amino acids 139 to 228. Partial sequence analyses of CNBr fragments and tryptic peptides identified two tightly clustered amino acid substitutions at amino acids 165 (Val to Met) and 173 (Lys to unknown). The substitutions in bm10 represent the most carboxy-terminal substitutions characterized in the Kb molecules of the spontaneous, histogenically active H-2 mutants.

Primary structure of the H-2Db alloantigen. II. Additional amino acid sequence information, localization of a third site of glycosylation and evidence for K and D region specific sequences

The complete amino acid sequence of the CNBr fragment comprising residues 229-284 of the murine major histocompatibility complex antigen H-2Db has been determined using radiochemical methodology. The sequence was determined by N-terminal sequence analysis of the intact CNBr fragment and by sequence determinations of peptides derived from this fragment by trypsin and staphylococcal V8 protease cleavage. In addition to the amino acid assignments for H-2Db, it was possible to assign the linkage position of the third N-linked glycosyl unit to the asparagine at residue 256. Additional amino acid sequence assignments have also been made for three other CNBr fragments that span residues 99-138, 139-228, and 308-331 of the H-2Db molecule. The total protein sequence information available (222 of 338 residues) agrees in every comparable position with the protein sequence derived from the cDNA clone (pH203) isolated by Reyes and co-workers (1982b), which strongly suggests that this clone encodes H-2Db. Combination of the protein sequence with that deduced from the cDNA clone provides the complete H-2Db protein sequence. Comparison of this sequence with other available protein sequence information for murine class I molecules has revealed protein sequences that may be unique to either K or D region molecules.

Biochemical studies on the H-2K antigens of the MHC mutant bml

Biochemical analysis of the H-2K-gene product from the MHC mutant strain bml and from the C57BL/6 parent strain has been carried out in order to characterize the structural differences between parent and mutant K-gene products. Based on comparative tryptic peptide mapping of the cyanogen bromide fragments from these glycoproteins, two peptide differences were localized to the CN-Ia fragment. Partial amino-acid sequence analysis revealed two alterations in the primary structure of Kbml involving substitutions of tyrosine for arginine at position 155, and tyrosine for leucine at position 156. Both of these amino-acid replacements require a minimum of two nucleotide base changes at the nucleic acid level. These changes were the only alterations noted differentiating the Kbml and Kb glycoproteins. However, because our techniques allow us to analyze only 75 to 80 percent of the extra cellular portion of H-2Kb, it is possible there are other undetected changes. Nonetheless, the biochemical data are consistent with the hypothesis that the structural alterations noted in the Kbml mutant glycoprotein are directly related to the observed immunological specificity relative to the parent Kb molecule. Peptide comparisons of the Kb molecules of two C57BL/6 sublines and of the H-2b lymphoblastoid cell line, EL-4, disclosed no difference.

Amino acid sequence of the carboxyl-terminal hydrophilic region of the H-2Kb MHC alloantigen. Completion of the entire primary structure of the H-2Kb molecule

The amino acid sequence of the COOH-terminal hydrophilic region of the H-2Kb histocompatibility antigen was determined. The sequence was completed by analyses of four CNBr fragments obtained from the intact molecule as well as tryptic peptides. This region was composed of 39 amino acid residues with a cluster of basic residues at the NH2 terminus and localized positions 308-346 of the H-2Kb molecule. These sequence data, together with those reported for the NH2-terminal 284 residues [Martinko, J. M., Uehara, H., Ewenstein, B. M., Kindt, T. J., Coligan, J. E., & Nathenson, S. G. (1980) Biochemistry 19, 6188-6193] and for the intramembranous segment [Uehara, H., Coligan, J. E., & Nathenson, S. G. (1981) Biochemistry (preceding paper in this issue)], provided the complete primary structure of the H-2Kb molecule. This is the first histocompatibility antigen for which the entire primary structure is determined.

Isolation and sequence analysis of the intramembranous hydrophobic segment of the H-2Kb murine histocompatibility antigen

The primary structure of the intramembranous segment (TC-1) of the mouse transplantation antigen, H-2Kb, has been determined. The segment contains a stretch of 31 uncharged amino acid residues and is localized between the NH2-terminal and the COOH-terminal hydrophilic regions of the molecule. The amino acid sequence of TC-1 is Trp-Asp-Glu-Pro-Pro-Ser-Thr-Val-Ser-Asn-Met-Ala-Thr-Val-Ala-Val-Leu-Val-Val-Leu -Gly-Ala-Ala-Ile-Val-Thr-Gly-Ala-Val-Val-Ala-Phe-Val-Met-Lys-Met-Arg-(Arg)-(Arg ).

Complete amino acid sequence of murine beta 2-microglobulin: structural evidence for strain-related polymorphism

Primary structural analyses of beta 3-microglobulin isolated from the tumor cell lines EL4.BU (derived from a C57BL/6 mouse) and C14 (derived from a BALB/c mouse) have revealed the presence of an amino acid difference at position 85 of this molecule. beta 2-Microglobulin isolated from histocompatibility antigens of EL4.BU has alanine at this position, whereas that from C14 has aspartic acid. Determination of the sequence of these molecules has employed radiochemical methodology that was developed in studies of murine histocompatibility antigens. The sequence obtained in this study is: Ile - Gln - Lys - Thr - Pro - Gln - Ile - Gln - Val - Tyr - Ser - Arg - His - Pro - Pro - Glu - Asn - Gly - Lys - Pro - Asn - Ile - Leu - Asn - Cys - Tyr - Val - Thr - Gln - Phe - His - Pro - Pro - His - Ile - Glu - Ile - Gln - Met - Leu - Lys - Asn - Gly - Lys - Lys - Ile Pro - Lys - Val - Glu - Met - Ser - Asp - Met - Ser - Phe - Ser - Lys - Asp - Trp - Ser - Phe - Tyr - Ile - Leu - Ala - His - Thr - Glu - Phe - Thr - Pro - Thr - Glu - Thr - Asp - Thr - Tyr - Ala - Cys - Arg - Val - Lys - His - Ala/Asp - Ser - Met - Ala - Glu - Pro - Lys - Thr - Val - Tyr - Trp - Asp - Arg - Asp - Met. Comparison of the sequence of murine beta 2-microglobulin to the sequences reported for the homologues from man, rabbit, and guinea pig indicate identities of 68%, 66%, and 61%, respectively.

Primary structure of murine major histocompatibility alloantigens: amino acid sequence of the cyanogen bromide fragment Ia (positions 139-228) from the H-2Kb molecule

The complete amino acid sequence of the cyanogen bromide (CNBr) fragment Ia (CN-Ia) from the murine histocompatibility antigen H-2Kb has been obtained by using radiosequence methodology. This glycopeptide is the largest CNBr cleavage product of the H-2K molecule and extends from position 139 to position 228. The sequence determined for CN-Ia was Ala-Ala-Leu-Ile-Thr-Lys-His-Lys-Trp-Glu-Gln-Ala-Gly-Glu-Ala-Glu-Arg-Leu-Arg-Ala -Tyr-Leu-Glu-Gly-Thr-Cys-Val-Glu-Trp-Leu-Arg-Arg-Tyr-Leu-Lys-Ans-Gly-(Asn)-Ala- Thr-Leu-Leu-Arg-Thr-Asp-Ser-Pro-Lys-Ala-His-Val-Thr-His-His-Ser-Arg-Pro-Asp-Asp -Lys-Val-Thr-Leu-Arg-Cys-Trp-Ala-Leu-Gly-Phe-Tyr-Pro-Ala-Asp-Ile-Thr-Leu-Thr-Tr p-Gln-Leu-Asn-Gly-Glu-Glu-Leu-Ile-Gln-Aps-Met. The data were obtained by analysis of fragments derived by thrombic, tryptic, chymotryptic, and V8 protease digestion of CN-Ia. A carbohydrate moiety is attached to Asn at position 176. Homology between this 90 amino acid stretch of H-2Kb and HLA-B7 [Orr, H. T., Lopez de Castro, J. A., Lancer, D., & Strominger, J. L. (1979) Biochemistry 18, 5711] is 68%, and differences are noted at positions 176, 177, and 178 which in the H-2 molecule are the attachment region for a second carbohydrate moiety. No carbohydrate was detected in this position for HLA-B7 [Orr, H. T. Lopez de Castro, J. A. Lancet, D., & Strominger, J. L. (1979) Biochemistry 18, 5711].

Primary structure of murine major histocompatibility complex alloantigens: completion of the sequence of the amino-terminal 284 residues of H-2Kb

The primary structure of the COOH-terminal cyanogen bromide (CNBr) cleavage fragment Ic (CN-Ic) of the extracellular portion of the murine histocompatibility antigen H-2Kb has been completed. CN-Ic contains a site of papain cleavage which has been utilized for solubilizing H-2Kb by cleaving off the membrane integrating portion of the molecule. The amino acid sequence of CN-Ic has been determined by using peptides recovered after trypsin digestion of CN-Ic before and after blockage of lysine groups with citraconic anhydride. Overlapping sequences for the tryptic fragments were obtained by amino-terminal sequence analysis. The sequence of fragment CN-Ic, which spans residues 229-284 in H-2Kb, is as follows: Glu-Leu-Val-Glu-Thr-Arg-Pro-Ala-Gly-Asp-Gly-Thr-Phe-Gln-Lys-Trp-Ala-Ser-Val-Val-Pro-Leu-Gly-Lys-Glu-Gln-Tyr-Tyr-Thr-Cys-His-Val-Tyr-Gln-Gln-Gly-Leu-Pro-Gln-Pro-Leu-Thr-Leu-Arg-Trp-Asp-Glu-Pro-Pro-Ser-Thr-Val-Ser-Asn-Met. This amino acid sequence determination completes the primary structure of the amino terminal 284 residues of H-2Kb, that portion of this histocompatibility antigen which is external to the cell membrane and which contains antigenic determinants. It was also possible to identify Val-281 as a papain cleavage site within CN-Ic. The completed structure was analyzed solely by radiochemical methods. The structure obtained for H-2Kb is 71% homologous to the reported structure of HLA-B7, a human homologue.

Biochemical studies on the H-2K antigens of the MHC mutants bm3 and bm11

Biochemical analyses of the H-2K-gene products of the C57BL/6 mutant strains, bm3 and bm11, have been carried out in order to characterize the structural relationships among these antigens. From comparative tryptic peptide mapping of cyanogen bromide fragments from the mutant and parent Kb glycoproteins and from preliminary amino-acid sequence analyses, a number of discrete differences have been discerned. Two sites of difference at amino residues 77 and 89 in the Kbm3 glycoprotein are noted relative to Kb. An alteration at residue 77 similar or identical to that seen in Kbm3 is present in the K antigen of the bm11 mutant. Because our techniques sample only 75 to 80 percent of the extracellular portion of H-2Kb, other undetected changes are possible. However, our present findings are most consistent with the conclusion that only very limited differences exist between mutant and parent molecules. Further, taken together with CML (cell-mediated-lymphocytotoxicity) reaction patterns (Melief et al. 1980), the biochemical data support the hypothesis that the proposed structural alterations in the Kb mutant glycoproteins are directly related to their observed immunological specificity.

Purification and partial characterization of high-molecular-weight forms of ectopic calcitonin from a human bronchial carcinoma cell line

Studies on the high-molecular-weight immunoreactive calcitonin produced ectopically in culture by an epidermoid bronchial carcinoma cell line are reported. In cell-exposed medium, the principal component has a molecular weight of 40000 and molecules of mol.wts. 13000 and 10000 also occur. Only a trace amount of material co-eluting with 35000-mol.wt. human calcitonin is detectable. None of the calcitonins show cross-reactivity with anti-corticotropin serum. The 40000-mol.wt. immunoreactive calcitonin is readily proteolysed to the 13000- and 10000-mol.wt. components, but the 10000-mol.wt. component behaves as a comparatively stable 'core' molecule. By using immunoprecipitation and high-pressure liquid chromatography (h.p.l.c.), it is possible to prepare radiochemically homogeneous 10000-mol.wt. immunoreactive calcitonin from cells grown in the presence of individual 35S- or 3H-labelled amino acids. Peptide mapping of enzymic digests of this material by h.p.l.c. shows that it contains peptides in common with synthetic human calcitonin.

Structure of the heavy chain of the H-2Kk histocompatibility antigen

We have used radiochemical techniques to characterize the heavy chain (Mr 46,000) of the murine H-2Kk histocompatibility antigen in terms of six fragments (I-VI) obtained after cleavage of the polypeptide chain with CNBr. The tentative order of the fragments, which account for more than 90% of the heavy chain, was assigned by radiochemical sequence analysis of the intact heavy chain and of each purified CNBr fragment and by analysis of the CNBr fragments obtained from the large papain fragment of the heavy chain. Treatment of cells with tunicamycin yielded H-2 molecules with heavy chains of molecular weight 40,000, suggesting that the carbohydrate moieties have a combined molecular weight of approximately 6000. CNBr cleavage of H-2Kk heavy chains labeled with [3H]fucose indicated that the carbohydrate moieties are located on fragments II and IV.. Incubation of cells with 32PO4 gave H-2 molecules with radioactive phosphoserine in the carboxyl-terminal CNBr fragment (VI) of the heavy chain and in the fraction containing beta 2-microglobulin. Sequence analysis of each CNBr fragment intrinsically labeled with 3H- and 35S-labeled amino acids identified a total of 87 residues in the H-2Kk heavy chain. The sequence closely resembles that of the H-2Kb molecule, and the 11 differences are scattered throughout the polypeptide chain. Comparison with HLA sequences indicates that the two allelic H-2 sequences are more closely related to each other (88% identity) than either is to the HLA-B7 or A2 antigens (approximately 70%). Similarly, the nonallelic HLA antigens are more closely related to each other (83%) than either is to the H-2Kk or H-2Kb molecules.

Isolation, characterization and amino acid sequence studies of the cyanogen bromide fragments of the H-2Dd glycoprotein

The papain-solubilized fragment of the H-2Dd antigen, representing the NH2-terminal 80% of the native glycoprotein, can be fragmented into five polypeptides using CNBr cleavage. These fragments have been isolated, characterized and subjected to amino acid sequence analysis using radiochemical microtechniques. It was possible to align these CNBr fragments by comparison of their NH2-terminal amino acid sequence with the known amino acid sequence of the H-2Kb molecule. Thus, the NH2-terminal fragment, D, contains 23 residues and is followed by a glycopeptide, fragment C, of 75 residues. Following fragment C are three fragments held together by disulfide bonds: fragment b4, which has 40 amino acid residues, a second glycopeptide, fragment b2, of 90 residues, and fragment b3, a peptide of approximately 55 residues which terminates at the site of papain cleavage. The complete amino acid sequence of the NH2-terminal CNBr fragment, D, has been determined, and this is presented here along with sequence data for the NH2-terminal 30 residues of each of the other four CNBr fragments of the papain fragment of H-2Dd. A total of 146 positions have been examined in the approximately 280-residue H-2Ddpapain molecule, and a total of 127 residues have been positively determined. Most of the unassigned positions may be tentatively assigned as Asp or Asn, the only amino acids so far not incorporated in radiolabeled form by our metabolic labeling procedures into the H-2Dd molecule. Comparison of the sequence data obtained for the H-2Dd molecule to data available for other histocompatibility antigens revealed homologies of approximately 90% with H-2Kb and H-2Ld, and approximately 75% with HLA-B7 and HLA-A2.

Primary structural studies of an H-2L molecule confirm that it is a unique gene product with homology to H-2K and H-2D antigens

Radiochemical methodology has been used in the isolation and preliminary biochemical characterization of the murine H-2Ld major histocompatibility complex gene product. The radiolabeled molecule was isolated by immunoprecipitation from the glycoprotein fraction of detergent-solubilized H-2d tumor cells. Six major CNBr fragments were isolated from a papain fragment of this molecule; three of the fragments are connected by disulfide bonds. Due to the high degree of homology between major transplantation antigens, it was possible to align the fragments by comparison of their amino acid sequences to that of the H-2Kb gene product. Of the positions available for comparison between H-2Ld and H-2Kb, H-2Dd, and H-2Kd gene products, 61 out of 80 (78%), 45 out of 55 (82%), and 12 out of 15 (80%), respectively, are identical. Differences between the Ld and Kb and Dd molecules are distributed throughout the amino acid sequence. These data indicate that the H-2Ld gene product is a molecular species distinct from, but homologous to, the H-2K and H-2D gene products.

Biochemical evidence for a separate, MHC-linked locus encoding H-2.28 antigens

In comparing the tryptic peptide maps of the H-2L and H-2D glycoprotein antigens isolated from NP-40 lysates of RADA1 (H-2 alpha) leukemic cells, no more than 37% of the observed arginine-containing tryptic peptides are found to be homologous. Thus, the primary amino-acid sequences of these two antigens are probably less than 90% homologous. This constitutes the strongest evidence to date that the MHC-linked H-2L region encodes H-2L antigens separately from the H-2D region, even though H-2L antigens bear D-end-associated antigenic determinants of the H-2.28 family. The anti-H-2.28 alloantiserum (k X r anti h2) used to precipitate H-2L antigens in this investigation was the NIH contract antiserum D28b. As the tryptic peptide maps also suprisingly revealed, D28b precipitates H-2D antigens as well and, thus, anti-H-2.4 immunoadsorbants were employed to isolate H-2L free of H-2D antigens. In light of the dual specificity of D28b, its reactivity with BALB/c-H-2dm2 mutant cells was re-examined. Even though mutant lymphocytes, which lack H-2L but not H-2D antigens, are not cytotoxically lysed by D28b (as are parental H-2d cells), D28b appears to precipitate H-2D antigens from NP-40 extracts of mutant splenocytes.

Primary structure of murine major histocompatibility complex alloantigens: amino acid sequence studies of the cyanogen bromide fragments of the H-2Kb glycoprotein

Radiochemical microtechniques have been used in the amino acid sequence analysis of five major CNBr fragments of the glycoprotein specified by the murine major histocompatibility complex gene H-2k(b). These fragments have been tentatively aligned and represent the NH(2)-terminal 80% of the intact molecule. All amino acids except Asp, Asn, and Gln have been assigned in 128 out of 149 possible positions in the NH(2)-terminal portions of each of these fragments. These assignments, which represent approximately 50% of the total sequence from these fragments, are listed below in the order of their alignment in the intact H-2K(b) molecule: IIIn, -PHSLRYFVTAVSRP(G)L(G)(E)PRYM; IIIa, EVGYV--TEFVRF-S-AE(A)PRYEPR(A)--M; Ib, E-EGPEYWERET-KAK(G)-E-SFR--LRTLL(G)YY--TK; Ia, AALITK-KWE-AGEAERLRAYLEGTC-E-L; Ic, ELVETRPAG-GTF-KWAS-VVPLGKE-YY(T). The unassigned positions represented by dashes in the above sequences may be tentatively assigned as Asp, Asn, or Gln. The NH(2)-terminal sequence obtained for the H-2K(b) molecule was compared to the limited sequence information available for other major histocompatibility complex gene products. An 84% homology (16 of 19 residues) to the H-2K(q) and H-2K(k) molecules, which are identical to one another in the positions compared, was observed. A similar comparison with 28 of the 31 NH(2)-terminal residues of HLA-B7 indicated 68% homology. Furthermore, significant homology was observed between H-K(b) and HLA-B7 in a region of glycosylation, which occurs between positions 85 and 100 in the two molecules.

Structural evidence that the small subunit found associated with the TL antigen is beta 2-microglobulin

Comparative tryptic peptide mapping and partial amino-terminal primary sequence analysis of the light chain component associated with the TL antigens showed that the small subunit of TL was identical to the beta 2m light chain associated with the H-2K or D product of the same strain. Peptide comparison of the beta 2m from the Tla products of an A strain X-ray induced leukemia RADA1 (Tlaa) and of a C57BL/6 strain X-ray induced leukemia ERLD (Tlab) showed differences to the extent of 25-35% in their peptides. This is consistent with previous results showing beta 2m allelic variations between these mouse strains. The data prove the structural identity of the beta 2m molecules from TL and H-2K, D antigens as well as reveal the strain specific polymorphism of the beta 2m associated with these products.