Blood Cells - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 64

3.5.3.1 Plasmalemmal Proteins

Transmembrane proteins include anion transporter SLC4a1; 24 glycophorin-A, -B,
and -C; Rhesus blood group (Rh); Rh-associated glycoprotein (RhAG); Duffy;
basal cell adhesion molecule (bCAM); 25 intercellular adhesion molecule ICAM4; 26
heparan sulfate proteoglycan epican (Indian blood group; a.k.a. CD44); integrin-
associated protein CD47; Kell blood group metalloendopeptidase; and X-linked Kx
blood group (XK).
Erythrocyte markers Rh and RhAG could be gas transporter. In addition, RhAG
and Rh form the Rh complex with CD47, LW, and glycophorin-B. Duffy serves
as a chemokine receptor. Markers BCAM, ICAM4, and epican, are involved in
cell adhesion. Kell blood group metalloendopeptidase has an endothin-3-converting
enzyme activity.
Transporter SLC4a1 is the preponderant transmembrane constituent of the
RBC membrane that operates as an anion exchanger. It binds protein-4.2, he-
moglobin, glycolytic enzymes (aldolase, phosphofructokinase, and glyceraldehyde
3 -phosphate dehydrogenase), and carbonic anhydrase-2 to form the metabolon .
Furthermore, SLC4a1 tetramer interacts with glycophorin-A to build the SLC4a1-
ankyrin complex that is attached by ankyrins to spectrin tetramers.

3.5.3.2 Connections between the Plasma Membrane and Cytoskeleton

The cell cortex lattice is composed of spectrin tetramers formed by self-association
of heterodimers made of -spectrin. Spectrin tetramers are attached to junc-

tional complexes that comprise short F actin protofilaments and several actin-binding
proteins, such as protein-4.1R, dematin (protein-4.9), adducin, tropomyosin, and
tropomodulin.
Ankyrins link the spectrin-actin cytoskeleton to the membrane. Ankyrin defi-
ciency is also known as hereditary spherocytosis. Ankyrins bridge the spectrin-actin
cytoskeleton and SLC4a1 tetramers, as well as proteins involved in ion transfer,
such as Cl − -HCO 3 anion exchanger, Na + -Ca 2 + exchanger, Na + -K + AT P a s e ,
IP 3 receptor, ryanodine receptor-Ca 2 + channel, and voltage-gated Na + channels
(Na V )[ 115 ].
Protein-4.1R, dimeric SLC4a1, adducin, spectrin, and actin form an additional
multifunctional, multiproteic complex of the RBC membrane with transmembrane
glycophorin-C, palmitoylated membrane protein MPP1, 27 Rh, Duffy, Kell, and XK:
the so-called 4.1R-based complex that surrounds connections between the cortical
cytoskeleton and plasma membrane [ 116 ].

α -and β

24 A.k.a. erythrocyte membrane protein band-3 and anion exchanger AE1.
25 A.k.a. Lutheran blood group glycoprotein (Lu antigen) and CD239.
26 A.k.a. Landsteiner-Wiener blood group glycoprotein (LW) and CD242.
27 A.k.a. 55-kDa erythrocyte membrane protein P55.