|Blood Group Antigen Gene Mutation Database|
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Landsteiner-Wiener Blood Group System
Gene locus - ICAM4
The protein carrying the antigens for the Landsteiner-Wiener blood group system is a product of a single gene, ICAM4 which consists of 3 exons distributed over 2.65 kb. The gene encodes a type I integral membrane glycoprotein of 241 residues in glycosylated form; its size, by Western blotting, is 42kD. The LW protein is a member of the Ig superfamily and bears similarity in sequence (30% identity) and structure to the intercellular adhesion molecules, ICAMs; in fact, LW, ICAM-1, and ICAM3 may have evolved by duplication from a common ancestral gene. Its binding to leukocyte-specific integrins parallels that of ICAMs.LW designation is ICAM-4.
ICAM transcripts are present in a number of isoforms ; thus the choice of a correct reference sequence when identifying alleles is essential.
Function of proteins
Plays a role in intercellular adhesion and is a ligand for integrins. Is a component of the Rh macromolecular compllex.
Each ICAM isomer has a characteristic tissue distribution, LW (ICAM-4) being expressed predominantly in erythroid cells.
None known; however, LW antigens may be depressed during pregnancy and in some malignant states. LW protein expression is elevated in sickle erythrocytes and it seems to play a role in adhesion interactions of sickle cells as well as adhesion to endothelial cells and development of vaso-occlusion (Grandstaff-Moulds MK. Immunohematology 2011 27 136-142)
In the list of alleles, the Lwa reference sequence with accession number S78852 has been replaced by the sequence with accession number NM_001544.4, a full-length isoform encoding the Lwa phenotype (nt. 299A, aa 100Q). For alleles on the background of isoform 3 (the secreted form), sequence with accession number KF712272 is used. In the list of alleles, if a different 'reference' sequence than the above-mentioned ones is used to characterize an allele, the accession number for such 'reference' will be noted in the 'Comments' section of the allele's record. Note that the ICAM4 protein has a signal peptide of 30 residues that is not expressed at the membrane surface.
Other database IDs and links
Marion E. Reid and Christine Lomas-Francis, Immunohematology, New York Blood Center, 310 East 67 St, NY 10021
Contributors for specific alleles are listed with the alleles.
Updated 2014-04-25 03:57:25.267