Analysis in non-human primates reveals that the ancestral Band 3 gene encodes Dib and the Band 3-Memphis phenotype

Frequency of the DI*A, DI*B and Band 3 Memphis polymorphism among distinct groups in Brazil

INTRODUCTION

The Band 3 is a red blood cell protein that carries the Dia and Dib antigens from the Diego blood system. The SLC4A1 gene encodes Band 3; Band 3 Memphis is a polymorphism of normal Band 3 and has two variants, but only the variant II carries the Dia antigen.

OBJECTIVES

Describe the frequencies of the DI*A and DI*B alleles and the Band 3 Memphis among blood donors, sickle cell disease (SCD) patients and Amazonian Indians.

METHODS

A total of 427 blood samples were collected and separated into three groups: 206 unrelated blood donors, 90 patients with SCD and 131 Amazonian Indians. We performed DI*A/B, normal Band 3 and Band 3 Memphis genotyping, using the Polymerase Chain Reaction Restriction Fragment Length Polymorphism (PCR-RFLP).

RESULTS

The frequency of the DI*A/DI*A genotype was 0.5% in blood donors and it was not found in other groups. The frequency of the DI*A/DI*B was higher in Amazonian Indians (33.6%) and the frequency of the DI*B/DI*B was highest in blood donors (92.2%). All 105 individuals tested were positive for the presence of normal Band 3 and of these individuals, only 5/105 (4.8%) presented the Band 3 Memphis mutation.

CONCLUSION

We observed a higher frequency of the DI*B allele in blood donors and a low frequency of the DI*A/DI*A genotype in all groups studied. The Band 3 Memphis was found in a higher frequency in the blood donor group. Our findings highlight the importance of analyzing different population groups to gain a better understanding of the genetic association of blood group antigens.

Band 3, the human red cell chloride/bicarbonate anion exchanger (AE1, SLC4A1), in a structural context

The crystal structure of the dimeric membrane domain of human Band 3(1), the red cell chloride/bicarbonate anion exchanger 1 (AE1, SLC4A1), provides a structural context for over four decades of studies into this historic and important membrane glycoprotein. In this review, we highlight the key structural features responsible for anion binding and translocation and have integrated the following topological markers within the Band 3 structure: blood group antigens, N-glycosylation site, protease cleavage sites, inhibitor and chemical labeling sites, and the results of scanning cysteine and N-glycosylation mutagenesis. Locations of mutations linked to human disease, including those responsible for Southeast Asian ovalocytosis, hereditary stomatocytosis, hereditary spherocytosis, and distal renal tubular acidosis, provide molecular insights into their effect on Band 3 folding. Finally, molecular dynamics simulations of phosphatidylcholine self-assembled around Band 3 provide a view of this membrane protein within a lipid bilayer.

Molecular population genetics of SLC4A1 and Southeast Asian ovalocytosis

Southeast Asian ovalocytosis (SAO) is an erythrocyte abnormality that protects affected individuals from cerebral malaria. This trait is caused by a 27-bp deletion in the SLC4A1 gene, which is lethal when homozygous. We reseqeunced approximately 5 kb of SLC4A1 in an Indonesian population where SAO is prevalent to better understand the evolution of this clinically important trait. The four SAO chromosomes we resequenced share a single haplotype that differs from a sampled non-SAO haplotype only by the 27-bp deletion. Comparison of Indonesian sequence data to that from two other Asian populations (aboriginal Taiwanese and Japanese) shows Indonesian SLC4A1 to be strongly differentiated from the Taiwanese, but not the Japanese. Indeed, the Taiwanese sample contains only chromosomes that are highly divergent from all sampled SAO chromosomes. Because earlier studies have found an association between Austronesian-speakers (who most likely originated in Taiwan) and SAO, our failure to find SAO-like chromosomes in Taiwan is unexpected. Finally, our data find a strong excess of high-frequency derived alleles in all three populations. These alleles include the non-synonymous 'Memphis' variant, which is known to affect anion transport across the erythrocyte membrane. Our data suggest a role for recent natural selection acting on Memphis or a linked variant.