Tryptic peptide map analyses of mouse transplantation antigens

Concerted evolution of class I genes in the major histocompatibility complex of murine rodents

Full-length cDNA sequences of two class I major histocompatibility complex molecules from the DA strain of Rattus norvegicus are reported. One codes for the classical class I restriction element RT1.Aa, which maps to the locus in the rat major histocompatibility complex homologous to H-2K in the mouse. The other probably codes for a soluble nonclassical class I molecule present in DA rat serum; a short deletion in the fifth exon implies that the translated product will terminate in the membrane-spanning region. These sequences have been compared with mouse classical class I sequences as well as with three published rat class I cDNA partial sequences. The results show, first, that "locus-specific" substitutions from the H-2K, H-2D, and H-2L data set are scrambled in the RT1.Aa molecule; a majority of these substitutions have H-2D/L-specific features. Second, the data show that the four rat sequences are strikingly similar to one another regardless of locus or haplotype of origin; they share a number of apparently species-specific features that distinguish them all from mouse classical class I sequences, which likewise share distinctive features of their own. The results suggest that segmental sequence exchange plays a major role in determining the evolution of sequence in class I major histocompatibility complex molecules.

Carbohydrate moieties of rat MHC class I antigens

The rat major histocompatibility complex class I antigens RT1.Au and RT1.Eu from the u haplotype and RT1. An from the n haplotype were labeled with 14C-asparagine or with 3H-fucose, mannose, galactose, and N-acetylglucosamine. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed complete removal of radioactivity from the sugar-labeled antigen heavy chains by digestion with glycopeptidase F, an enzyme that removes N-linked glycans completely. High performance liquid chromatography analysis of the tryptic digests of the mixed sugar-labeled and asparagine-labeled antigens demonstrated that all the sugar-labeled peptides were coincident with asparagine-labeled peptides. The An antigen showed three glycopeptides, each of which had different amounts of sugar radioactivity. The antigens Au and Eu showed two glycopeptides with different amounts of radioactivity but at identical positions in the two antigens. Antigen Eu had an additional glycopeptide with a lower amount of radioactivity. The positions of the glycopeptides from the Au and Eu antigens were different from those of the An antigen. The peptide profiles of the 14C-asparagine-labeled Au and Eu antigens demonstrated distinct differences between the molecules. The results of this study show that: (a) all the glycans on rat class I antigens are N-linked, as they are on H-2 and HLA class I antigens; (b) there are compositional differences among the glycans in each of the three antigens; (c) the glycosylation pattern of the rat class I antigens is similar to that of the mouse class I antigens, which contain two or three glycans, in contrast to that of the human class I antigens, which contain only one glycan; and (d) the antigens Au and Eu from the same haplotype are more closely related to each other than they are to the An antigen.

Comparison of rat MHC class I antigens by peptide mapping

Monoclonal antibodies specific for the rat major histocompatibility complex (MHC) class I antigens RT1.An, RT1.Au, and RT1.Eu were used for immunoprecipitation of antigens biosynthetically radiolabeled with 14C- or 3H-labeled arginine, lysine, and tyrosine; with arginine or tyrosine alone; and with or without tunicamycin in the culture medium. Heavy chains of the glycosylated and unglycosylated antigens were purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and their tryptic and chymotryptic peptides were compared by high performance liquid chromatography. The antigens coded by the same locus in two different haplotypes (An and Au) differed by 30%, whereas the products of two different loci in the same haplotype (Au and Eu) differed only by 1-3%. Comparative analysis of the data for samples labeled with single amino acids indicated that two amino acids in Au have been substituted by an arginine and probably by a tyrosine residue, respectively, in Eu. The high degree of homology between the products of the A and E loci in the same haplotype accounts for the difficulty in detecting recombinational events within the MHC of the rat by classical serological approaches.

Biochemical documentation of allelic variation of the I-E antigens of the d, k, p, r, and u haplotypes

The extent of allelic variation of the E alpha and E beta polypeptide chains of the I-E antigens from the H-2d, H-2k, H-2p, H-2r, and H-2u haplotypes is described. E alpha and E beta chains were individually labeled with arginine or lysine and compared by tryptic peptide analysis. The results indicate minimum variability among the E alpha polypeptides encoded by the d, k, p, and r haplotypes. However, the Eu alpha chain differed significantly from the other allelic E alpha gene products. On the other hand, the E beta alleles demonstrated substantial variability with the Ed beta being notably less similar to the other alleles than they are to each other. These findings are consistent with a number of observations regarding the serology and functions of the I-E antigens.