Tertiary structural changes associated with iron binding and release in hen serum transferrin: a crystallographic and spectroscopic study.
The iron binding and release of serum transferrin are pH-dependent and accompanied by a conformational change between the iron-bound (holo-) and iron-free (apo-) forms. We have determined the crystal structure of apo-hen serum transferrin (hAST) at 3.5A resolution, which is the first reported structure to date of any full molecule of an apo-serum transferrin and studied its pH-dependent iron release by UV-vis absorption and near UV-CD spectroscopy. The crystal structure of hAST shows that both the lobes adopt an open conformation and the relative orientations of the domains are different from those of apo-human serum transferrin and human apolactoferrin but similar to that of hen apo-ovotransferrin. Spectroscopic analysis reveals that in hen serum transferrin, release of the first iron starts at a pH approximately 6.5 and continues over a broad pH range (6.5-5.2). The complete release of the iron, however, occurs at pH approximately 4.0. The near UV-CD spectra show alterations in the microenvironment of the aromatic residues surrounding the iron-binding sites.
Thakurta
Piyali Guha
PG
Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064, India.
Choudhury
Debi
D
Dasgupta
Rakhi
R
Dattagupta
J K
JK
D000818:Animals; D001665:Binding Sites; D001774:Blood Chemical Analysis; D002645:Chickens; D002942:Circular Dichroism; D003198:Computer Simulation; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D005260:Female; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D046911:Macromolecular Substances; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*; D014168:Transferrin / Q000737:chemistry*
D046911:Macromolecular Substances; D014168:Transferrin; D007501:Iron