Cargando…

Magnetic circular dichroism studies of iron(ii) binding to human calprotectin

Calprotectin (CP) is an abundant metal-chelating protein involved in host defense, and the ability of human CP to bind Fe(ii) in a calcium-dependent manner was recently discovered. In the present study, near-infrared magnetic circular dichroism spectroscopy is employed to investigate the nature of F...

Descripción completa

Detalles Bibliográficos
Autores principales: Baker, Tessa M., Nakashige, Toshiki G., Nolan, Elizabeth M., Neidig, Michael L.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Royal Society of Chemistry 2017
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5361872/
https://www.ncbi.nlm.nih.gov/pubmed/28451278
http://dx.doi.org/10.1039/c6sc03487j
Descripción
Sumario:Calprotectin (CP) is an abundant metal-chelating protein involved in host defense, and the ability of human CP to bind Fe(ii) in a calcium-dependent manner was recently discovered. In the present study, near-infrared magnetic circular dichroism spectroscopy is employed to investigate the nature of Fe(ii) coordination at the two transition-metal-binding sites of CP that are a His(3)Asp motif (site 1) and a His(6) motif (site 2). Upon the addition of sub-stoichiometric Fe(ii), a six-coordinate (6C) Fe(ii) center associated with site 2 is preferentially formed in the presence of excess Ca(ii). This site exhibits an exceptionally large ligand field (10D (q) = 11 045 cm(–1)) for a non-heme Fe(ii) protein. Analysis of CP variants lacking residues of the His(6) motif supports that CP coordinates Fe(ii) at site 2 by employing six His ligands. In the presence of greater than one equiv. of Fe(ii) or upon mutation of the His(6) motif, the metal ion also binds at site 1 of CP to form a five-coordinate (5C) Fe(ii)–His(3)Asp motif that was previously unidentified in this system. Notably, the introduction of His-to-Ala mutations at the His(6) motif results in a mixture of 6C (site 2) and 5C (site 1) signals in the presence of sub-stoichiometric Fe(ii). These results are consistent with a reduced Fe(ii)-binding affinity of site 2 as more weakly coordinating water-derived ligands complete the 6C site. In the absence of Ca(ii), both sites 1 and 2 are occupied upon addition of sub-stoichiometric Fe(ii), and a stronger ligand field is observed for the 5C site. These spectroscopic studies provide further evaluation of a unique non-heme Fe(ii)–His(6) site for metalloproteins and support the notion that Ca(ii) ions influence the Fe(ii)-binding properties of CP.