X-ray Characterization of Conformational Changes of Human Apo- and Holo-Transferrin

• Published in: International journal of molecular sciences Vol. 22; no. 24; p. 13392
• Main Authors: Campos-Escamilla, Camila, Siliqi, Dritan, Gonzalez-Ramirez, Luis A, Lopez-Sanchez, Carmen, Gavira, Jose Antonio, Moreno, Abel
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 13.12.2021; MDPI
• Subjects: Binding sites; Binding Sites - physiology; Biochemistry & Molecular Biology; Biomedical materials; Chemistry; conformation change; Crystallization; Crystallography; Crystallography, X-Ray - methods; Crystals; Endocytosis; Glycosylation; human serum transferrin; Humans; Hydrogen-Ion Concentration; Iron; Iron - metabolism; Macromolecules; Models, Molecular; pH-dependence; Protein Binding - physiology; Protein Conformation; Proteins; Scattering, Small Angle; Serum - chemistry; Serum - metabolism; Small-Angle X-ray Scattering; Transferrin; Transferrin - metabolism; Transferrin - ultrastructure; Transferrins; X-ray Crystallography; X-Ray Diffraction; X-ray scattering; Small-Angle X-ray Scattering; human serum transferrin; conformation change; X-ray Crystallography; pH-dependence
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms222413392

Human serum transferrin (Tf) is a bilobed glycoprotein whose function is to transport iron through receptor-mediated endocytosis. The mechanism for iron release is pH-dependent and involves conformational changes in the protein, thus making it an attractive system for possible biomedical applications. In this contribution, two powerful X-ray techniques, namely Macromolecular X-ray Crystallography (MX) and Small Angle X-ray Scattering (SAXS), were used to study the conformational changes of iron-free (apo) and iron-loaded (holo) transferrin in crystal and solution states, respectively, at three different pH values of physiological relevance. A crystallographic model of glycosylated apo-Tf was obtained at 3.0 Å resolution, which did not resolve further despite many efforts to improve crystal quality. In the solution, apo-Tf remained mostly globular in all the pH conditions tested; however, the co-existence of closed, partially open, and open conformations was observed for holo-Tf, which showed a more elongated and flexible shape overall.