The low pKa value of iron-binding ligand Tyr188 and its implication in iron release and anion binding of human transferrin.
2D NMR-pH titrations were used to determine pKa values for four conserved tyrosine residues, Tyr45, Tyr85, Tyr96 and Tyr188, in human transferrin. The low pKa of Tyr188 is due to the fact that the iron-binding ligand interacts with Lys206 in open-form and with Lys296 in the closed-form of the protein. Our current results also confirm the anion binding of sulfate and arsenate to transferrin and further suggest that Tyr188 is the actual binding site for the anions in solution. These data indicate that Tyr188 is a critical residue not only for iron binding but also for chelator binding and iron release in transferrin.
Department of Chemistry, University of Hong Kong, Hong Kong, China.
Xuesong
X
Sun
Hongzhe
H
Sun
Ruiguang
R
Ge
Megan
M
Richter
Robert C
RC
Woodworth
Anne B
AB
Mason
Qing-Yu
QY
He
D000838:Anions / Q000378:metabolism; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001149:Arsenates / Q000378:metabolism; D001665:Binding Sites; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D008024:Ligands; D008239:Lysine / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011487:Protein Conformation; D013431:Sulfates / Q000378:metabolism; D017186:Titrimetry; D014168:Transferrin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism*
D000838:Anions; D001059:Apoproteins; D001149:Arsenates; D008024:Ligands; D013431:Sulfates; D014168:Transferrin; D014443:Tyrosine; D007501:Iron; D008239:Lysine; C025657:arsenic acid