Importance of Glycophorin A Protein Found in Red Blood Cells
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Glycophorin A (GpA) is a protein found in the human membrane red blood cell. The GpA protein is obtained from the gene called glycophorin A (MNS blood group) or GpA. The GpA gene bears the antigenic determinants for the MN and Ss blood groups, and 40 related variants of the Miltenberger complex and several isoforms of Sta1. There are two classes of membrane glycoproteins, asialo and sialoglycoproteins (glycophorins). These glycoproteins are determined by the presence of sialic acid which is the negative charge on cell surface. GpA is the primary sialoglycoprotein of human erythrocyte membranes that forms noncovalent dimers by sequence-specific, reversible association of its single hydrophobic membrane-spanning domain2. The glycophorin consists of four human genes GpA, GpB, GpC, and GpE that encode glycophorin proteins. GpA is characterized within the family of glycophorin under the glycophorin superfamily. GpA protein is found on the long arm of chromosome 4.
Figure 1: Dimeric transmembrane domain of Glycophorin A (PDB: 1AFO)3.
The sequence of the transmembrane GpA protein show that there are 80 amino acid residues. The sequence also shows 54 out of 80 residues are hydrophobic. The secondary structure of GpA protein reveals that these residues interact to form two same monomers, homodimer. Each of the dimer is an alpha helix containing 40 amino acids. According to RCSB protein databank, the homodimer is asymmetric as shown in figure 1. Alpha helices of GpA protein span at -400 to position an interface that lack hydrogen bonding within the monomers. The arrangement of the interface provides the physical basis for the interactions between the two helices. Two glycines are observed to help in the backbone-backbone contact of t...
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...hydrophilic. The sequence determine that the structure is two alpha helices embedded in the bilayer of the membrane while the N- and C-terminal are on the outside and inside of the membrane interacting with the hydrophilic environment. The structure of this membrane protein has significant biological functions such as virus binding, cell-surface antigenicity, cell-cell recognition, cell-cell communication, cellular transformation, transport, energy transduction4.
1. "GYPA." Genetics Home Reference. National Library of Medicine (US), 2014. Accessed: 16 Feb 2014. .
2. MacKenzie, K., J. Prestegard, and D. Engelman."A Transmembrane Helix Dimer: Structure and Implications." Science. 276. (1997): 131-3.
4. Tayyab, S., and M. Qasim. "Biochemistry and roles of glycophorin A." 16.2 (1988):