Murine Major Histocompatibility Complex Class-I Mutants: Molecular Analysis and Structure-Function Implications

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184

Diversity in 39 HLA-A, -B, and -C molecules is derived from 20 amino acid positions of high variability and 71 positions of low variability. Variation in the structurally homologous a, and a2 domains is distinct and may correlate with partial segregation of peptide and T-cell receptor binding functions. Comparison of 15 HLA-A with 20 HLA-B molecules reveals considerable locus-specific character, due primarily to differences at polymorphic residues. The results indicate that genetic exchange between alleles of the same locus has been a more important mechanism in the generation of HLA-A, -B, and -C diversity than genetic exchange events between alleles of different loci.Class I major histocompatibility complex glycoproteins are peptide-binding proteins that present processed antigens to cytotoxic T lymphocytes. The genes coding for these molecules are the most polymorphic loci known in higher vertebrates and for humans a total of 19 HLA-A, 37 HLA-B, and 8 HLA-C molecules have been defined (1). Although the basic features of class I molecules are well defined (2), accumulation of allelic sequences has been slow. The paucity of sequences has limited our understanding of the scope of the polymorphism, its function, and its generation. We present here a comparison of 39 HLA-A, -B, and -C sequences and a general assessment of their patterns of diversity. MATERIALS AND METHODSGenomic clones encoding HLA-A1, -B8, -B14, -B18, -Bw4l, -Bw42, -B44.2, -Bw65, and -Cw2.2 were isolated from the following cell lines: S. Gar (HLA-Aw24,3;B18,w41;Cw6), BB (HLA-Aw68.2,30;Bw42,w6S), FMB (HLA-AJ,32;$44,w57; Cw5,w6), MRWC (HLA-A2,32$JA,27;Cw2), MVL (HLAAw32;B27;Cw2), and LCL721 (HLA-Ai,2$.i,5). The cloned genes are underlined. Construction of libraries, isolation and identification of genes, and sequencing of genes with exonspecific oligonucleotide primers were as described (3). Genomic clones encoding HLA-A1 and HLA-B8 were kindly provided by H. T. Orr (University of Minnesota) (4).RESULTS AND DISCUSSION Variability in HLA-A, -B, and -C Molecules. Genes encoding HLA-A1, -B8, -B14, -B18, -B44, -Bw4l, -Bw42, -Bw65, and -Cw2 were isolated, and the exons were sequenced. The sequences of the HLA-B44 and HLA-Cw2 proteins each differ by 3 amino acids from identically typed molecules isolated from other cell lines (5, 6). These represent distinct subtypes, and we have designated them as HLA-B44.2 and HLA-Cw2.2 compared to HLA-B44.1 and HLA-Cw2.1 for the published sequences (5, 6). (a,, a2, and a3) that interact with antigenic peptides, the T-cell receptor, and the CD8 molecule. As single residues predominate at most positions, a consensus sequence can be made (Fig. 1). Individual molecules differ from the consensus by [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] residues, showing all have considerably diverged from a common ancestor.Without knowing the total number of alleles, it is difficult to predict how many sequences are required to gain an accurate description of HLA-A, -B, and -C polymorphism...

Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Nature of polymorphism in HLA-A, -B, and -C molecules.

Parham

Lomen

Lawlor

et al. 1988

341

184

“…Analyses of the mutant nucleotide sequences reveal that in the majority of occurrences multiple nucleotide substitutions were introduced into an acceptor gene by a donor gene. Typically, these substitutions fall in a region of overall high identity between the donor and acceptor genes (3). The variants can be classified into three categories.…”

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confidence: 99%

A complex major histocompatibility complexDlocus variant generated by an unusual recombination mechanism in mice

Yun

Melvold

Pease

1997

A spontaneous variant of the mouse class I major histocompatibility complex D b gene, designated D bm28 , is characterized. This mutation consists of a cluster of nucleotide substitutions in exon 3 that resembles the product of a classical gene conversion event in that the substituted nucleotides appear to be templated. However, D bm28 is distinctive, because no single donor gene containing the nucleotide sequence of the mutation exists in the genome of the parent strain. The mutation is consistent with the expected result of an interaction of two donor genes at the target locus during a single recombination event. While no known genetic mechanism gives rise to this class of mutation, we have established that 10 percent of spontaneous class I mutations in the mouse major histocompatibility complex have this complex phenotype. This process occurs at the D locus and the K locus. The significance of this kind of genetic interaction may extend beyond the major histocompatibility complex and have importance in shaping other multigene families.

“…It appears, however, that unconventional mutation mechanisms like segmental exchange (controversially referred to as gene conversion) are operative in HLA and H-2 systems. For HLA class I genes, interallelic segmental exchange predominates; interloci exchange is more evident in H-2 class I genes (10)(11)(12). Moreover, some of the events that led to MHC allelic variation are ancienti.e., they may antedate speciation of some primates and murine rodents (9)(10)(11)(13)(14)(15).…”

mentioning

confidence: 99%

Transmembrane domain length variation in the evolution of major histocompatibility complex class I genes.

Crew

Filipowsky

Neshat

et al. 1991

The fifth exons of major histocompatibility complex (MHC) class I genes encode a transmembrane domain (TM) that is largely responsible for class I antigen cell-surface expression usually through conventional hydrophobic amino acid-membrane interactions or, less often, through phosphatidylinositol linkage. In this report we show that Peromyscus lucopus, a Cricetidae rodent, has MHC class I genes (Pele-A genes) encoding three distinct sizes of TMs. Increases in TM lengths were due to tandem duplications ofsequences similar to human hypervariable minisatellite repeats and the A chi site. We discerned remnants of a similar duplication event in comparable rodent and primate MHC class I genes. Furthermore, several duplications and deletions appear to have occurred independently in H-2, RTI, Pele-A, and ChLA genes in near-identical positions. Accumulated data suggests that sequences in the fifth exon of MHC class I genes may, therefore, constitute a mutational or recoombinational hot spot that is mediated by minisatellite-and chi-like sequences imbedded within the coding region. The MHC class I genes may thus have recruited "selfish" DNA in their evolution to encode cell surface proteins. Expression of Pele-A genes was examined by the polymerase chain reaction (PCR) using oligonucleotide primers specific for exon 4 and 5 sequences. The PCR product sizes indicated that genes encoding each TM domain length are ubiquitously transcribed.