Practice question

Band 3 anion exchanger family SLC4A1 represents prototypical high abundance multi-pass transporter in human erythrocytes comprising about twenty five percent integral membrane protein. Full length nine hundred eleven amino acids organized into two domains: N-terminal cytoplasmic domain approximately four hundred three residues forming elongated dimeric structure binding ankyrin, protein 4.2, deoxyhemoglobin, and glycolytic enzymes including aldolase regulating metabolism; C-terminal membrane domain approximately five hundred residues comprising fourteen transmembrane helices arranged into two inverted repeats each seven helices forming core and gate domains exhibiting elevator-like transport movement confirmed by crystal structures of inward and outward facing states. Arg730 and Glu681 form selectivity filter catalyzing electroneutral exchange of chloride for bicarbonate at rate up to fifty thousand turnovers per second essential for carbon dioxide carriage. Glycophorin single-pass nineteen residues, GPCR seven-pass signaling, ankyrin peripheral adaptor not spanning. Mutations causing South Asian ovalocytosis, spherocytosis illustrate fourteen-span complexity enabling high-capacity anion flux without ATP hydrolysis using gradient energy.