X-ray Characterization of Conformational Changes of Human Apo- and Holo-Transferrin Campos Escamilla, Camila González Ramírez, Luis Antonio López Sánchez, Carmen Gavira Gallardo, José Antonio Moreno, Abel Small-Angle X-ray Scattering X-ray crystallography Human serum transferrin Conformation change pH-dependence DGAPA-PAPIIT project No. 207922. 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. 2022-01-07T11:55:55Z 2022-01-07T11:55:55Z 2021-12-13 journal article Campos-Escamilla, C... [et al.]. X-ray Characterization of Conformational Changes of Human Apo- and Holo-Transferrin. Int. J. Mol. Sci. 2021, 22, 13392. [https://doi.org/10.3390/ijms222413392] http://hdl.handle.net/10481/72237 10.3390/ijms222413392 eng http://creativecommons.org/licenses/by/3.0/es/ open access Atribución 3.0 España MDPI