DCS-1, DCS-2, and DFV share amino acid substitutions at the extracellular RhD protein vestibule.
BACKGROUND
RhD and RhCE are structurally related to ammonium transporter proteins, yet their physiologic function remains unclear. Recent three-dimensional homology modeling with Escherichia coli AmtB as a template defined a putative transmembraneous channel. Three RhD variants with amino acid substitutions located at the extracellular channel aperture are described.


METHODS
Blood samples were selected because of serologic abnormalities. RHD, RHCE, and LW nucleotide sequences were determined from genomic DNA. D epitope patterns were established with monoclonal anti-D panels. Three-dimensional Rh structures were calculated by alignment to AmtB.


RESULTS
The RHD allele DCS-1 was found to carry the two amino acid substitutions F223V (667T > G) and A226P (676G > C) caused by missense mutations in RHD exon 5. This study compared DCS-1 with the D variants DFV (F223V) and DCS-2 (A226P), harboring solely one or the other of the two substitutions. All three D variants were associated with a cDE haplotype. The antigen densities were approximately 3,000 D antigens per red blood cell for DCS-1, 800 for DCS-2, and 9,300 for DFV. DCS-1 and DCS-2 were partial D, because they lacked distinct epitopes. DFV presented as an almost normal D phenotype; the sample contained allo-anti-LW(a). The D(w) antigen was absent from DCS-1, DFV, and DAU-4, but expressed by DAU-5.


CONCLUSIONS
DCS-1, DCS-2, and DFV carry amino acid substitutions at the extracellular vestibule, visualized by 3-dimensional modeling. Proline at position 226 greatly influenced the D antigen density and may reduce the RhD membrane integration. Although the F223V substitution is regarded as the initial event in the evolution of the weak D Type 4 cluster, the current DFV allele probably evolved independently, as evident from different RHCE haplotypes.
Flegel
Willy A
WA
Institute for Transfusion Medicine, University Hospital Ulm, Ulm Germany. willy.flegel@uni-ulm.de
von Zabern
Inge
I
Doescher
Andrea
A
Wagner
Franz F
FF
Vytisková
Jindra
J
Písacka
Martin
M
D000483:Alleles; D019943:Amino Acid Substitution; D001483:Base Sequence; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D018604:Epitope Mapping; D000939:Epitopes; D019143:Evolution, Molecular; D005091:Exons; D006239:Haplotypes; D008958:Models, Molecular; D020125:Mutation, Missense; D011487:Protein Conformation; D012204:Rh-Hr Blood-Group System / Q000737:chemistry / Q000235:genetics* / Q000276:immunology
D015815:Cell Adhesion Molecules; D000939:Epitopes; C095100:ICAM4 protein, human; C066468:RHCE protein, human; D012204:Rh-Hr Blood-Group System; C026410:Rho(D) antigen