Organization of the gene for human erythrocyte membrane protein 4.2: structural similarities with the gene for the a subunit of factor XIII.

Abstract

Human erythrocyte band 4.2 is a major membrane-associated protein with an important, but still undefined, role in erythrocyte survival. We previously sequenced the complete cDNA for band 4.2 and showed that the protein has a strong sequence identity with the transglutaminase family of proteins but lacks transglutaminase activity. Here we have analyzed the genomic organization of band 4.2. The band 4.2 gene is =20 kilobases, consisting of 13 exons and 12 introns. Reticulocytes contain two different sized messages for band 4.2, and our results show that the major, smaller, message is produced by alternative splicing within band 4.2 exon I. The upstream region of the gene has several prospective promoter elements arranged in a pattern similar to that of two other erythroid genes, (3-globin and porphobilinogen deamiase.Alignment of the band 4.2 amino acid sequence with that of the a subunit of human coagulation factor XI and division of the sequences into exons reveal a remarkable correspondence, and in most cases identity, in the sizes of the paired exons. Moreover, each corresponding intron of the two genes is of an identical splice junction class. These and other similarities suggest that the gene for band 4.2 is closely related to and possibly derived from that for the a subunit of factor XIII and that the proteins may share common structural and functional properties.Human erythrocyte band 4.2 is a major membrane-associated protein of 72 kDa and is present at ==200,000 copies per cell (1, 2). Band 4.2 is clearly important for normal erythrocyte function since patients whose erythrocytes are deficient in or lack band 4.2 are anemic due to accelerated erythrocyte destruction and have abnormally shaped, possibly fragile, erythrocytes (3-5). In spite of this, however, the exact function of band 4.2 in the erythrocyte remains unclear. We have recently cloned and sequenced the full-length cDNA for band 4.2 (ref. 6; see also ref. 7). We found that the amino acid sequence of human erythrocyte band 4.2 has homology with two transglutaminases, guinea pig liver transglutaminase, and the a subunit of human coagulation factor XIII. The region of most striking identity includes a 49-amino acid domain of band 4.2, which is 69% and 51% identical to the corresponding domains of guinea pig liver transglutaminase and of the a subunit of factor XIII, respectively, and which spans the regions containing the active sites (8, 9) of both enzymes. However, band 4.2 has no demonstrable crosslinking activity when tested in vitro (6).In principle, the sequence similarities of band 4.2 with the transglutaminases could have arisen as the result of convergent evolution, in which each class of proteins evolved common, but as yet undetermined, functions independently, or, more likely, by divergent evolution, in which case the proteins would be expected to have arisen from a common ancestral gene. This question can be resolved by comparing the organization of the gene for band 4.2 with those of the transglutaminases, since a similar gen...

The Human Prostate-Specific Transglutaminase Gene (TGM4): Genomic Organization, Tissue-Specific Expression, and Promoter Characterization

“…Whereas there is a huge variation in intron sizes and thus in gene sizes (varying from 14.1 to over 160 kb), the number of introns and their localization are largely the same for the different TGase genes. The intron phases (Sharp, 1981) of corresponding introns are identical in all characterized TGase genes (Ichinose and Davie, 1988;Korsgren and Cohen, 1991;Phillips et al, 1992;Kim et al, 1994;Fraij and Gonzales, 1997). Comparison of their organization shows that the TGase genes can be divided into two subclasses.…”

“…The complete genomic structures of most other human TGases have been described (Ichinose and Davie, 1988;Korsgren and Cohen, 1991;Phillips et al, 1992;Kim et al, 1994;Fraij and Gonzales, 1997). Although the sizes of the various TGase genes range from approximately 14 kb [TGM1, the gene encoding TG K (Kim et al, 1992)] to over 160 kb [FXIIIa (Ichinose and Davie, 1988)], their basic organization and localization of introns are largely the same.…”

Role of factor XIII in fibrin clot formation and effects of genetic polymorphisms

“…86 Erythrocyte protein band 4.2 has significant sequence homology to the transglutaminases and is also a member of the family. 87 The factor XIII A-subunit gene has been localized to chromosome 6p24-p25 and shows linkage with the major histocompatibilty complex. 88,89 The gene codes for a mature protein of 731 amino acids, has 15 exons, and is more than 160 kilobases (kb) in size.…”

Protein-4.2 association with band 3 (AE1, SLCA4) in Xenopus oocytes: effects of three natural protein-4.2 mutations associated with hemolytic anemia

“…1 The protein-4.2 gene EPB42 contains 13 exons. 2,3 There are two isoforms of protein 4.2, a minor 74-kDa isoform obtained when all these exons of the gene are expressed and a 72-kDa major isoform of protein 4.2 that lacks 30 of the 33 amino acids that are encoded by exon 1. 4,5 The exact role of protein 4.2 in RBCs has not been elucidated, but protein 4.2 binds to the N-terminal cytoplasmic domain of the band-3 anion exchanger (AE1) and also interacts with ankyrin in RBCs.…”