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...
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| Format: | Article |
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Royal Society of Chemistry (RSC)
2018
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| Online Access: | http://hdl.handle.net/1721.1/113419 https://orcid.org/0000-0002-6234-8155 https://orcid.org/0000-0002-6153-8803 |
| _version_ | 1826203232567820288 |
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| author | Baker, Tessa M. Neidig, Michael L. Nakashige, Toshiki George Nolan, Elizabeth Marie |
| author2 | Massachusetts Institute of Technology. Department of Chemistry |
| author_facet | Massachusetts Institute of Technology. Department of Chemistry Baker, Tessa M. Neidig, Michael L. Nakashige, Toshiki George Nolan, Elizabeth Marie |
| author_sort | Baker, Tessa M. |
| collection | MIT |
| description | 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 His₃ Asp motif (site 1) and a His₆ 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[subscript q] = 11 045 cm⁻¹) for a non-heme Fe(ii) protein. Analysis of CP variants lacking residues of the His₆ 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 His₆ motif, the metal ion also binds at site 1 of CP to form a five-coordinate (5C) Fe(ii)-His₃ Asp motif that was previously unidentified in this system. Notably, the introduction of His-to-Ala mutations at the His₆ 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)-His₆ site for metalloproteins and support the notion that Ca(ii) ions influence the Fe(ii)-binding properties of CP. |
| first_indexed | 2024-09-23T12:33:24Z |
| format | Article |
| id | mit-1721.1/113419 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T12:33:24Z |
| publishDate | 2018 |
| publisher | Royal Society of Chemistry (RSC) |
| record_format | dspace |
| spelling | mit-1721.1/1134192022-09-28T08:36:12Z Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin Baker, Tessa M. Neidig, Michael L. Nakashige, Toshiki George Nolan, Elizabeth Marie Massachusetts Institute of Technology. Department of Chemistry Nakashige, Toshiki George Nolan, Elizabeth Marie 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 His₃ Asp motif (site 1) and a His₆ 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[subscript q] = 11 045 cm⁻¹) for a non-heme Fe(ii) protein. Analysis of CP variants lacking residues of the His₆ 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 His₆ motif, the metal ion also binds at site 1 of CP to form a five-coordinate (5C) Fe(ii)-His₃ Asp motif that was previously unidentified in this system. Notably, the introduction of His-to-Ala mutations at the His₆ 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)-His₆ site for metalloproteins and support the notion that Ca(ii) ions influence the Fe(ii)-binding properties of CP. National Institutes of Health (U.S.) (Grant P30-ES002109) 2018-02-05T16:24:46Z 2018-02-05T16:24:46Z 2016-10 2016-08 2018-02-01T13:04:24Z Article http://purl.org/eprint/type/JournalArticle 2041-6520 2041-6539 http://hdl.handle.net/1721.1/113419 Baker, Tessa M. et al. “Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin.” Chemical Science 8, 2 (2017): 1369–1377 © The Royal Society of Chemistry https://orcid.org/0000-0002-6234-8155 https://orcid.org/0000-0002-6153-8803 http://dx.doi.org/10.1039/C6SC03487J Chemical Science Creative Commons Attribution-NonCommercial 4.0 International http://creativecommons.org/licenses/by-nc/4.0/ application/pdf Royal Society of Chemistry (RSC) Royal Society of Chemistry |
| spellingShingle | Baker, Tessa M. Neidig, Michael L. Nakashige, Toshiki George Nolan, Elizabeth Marie Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin |
| title | Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin |
| title_full | Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin |
| title_fullStr | Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin |
| title_full_unstemmed | Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin |
| title_short | Magnetic Circular Dichroism Studies of Iron(ii) Binding to Human Calprotectin |
| title_sort | magnetic circular dichroism studies of iron ii binding to human calprotectin |
| url | http://hdl.handle.net/1721.1/113419 https://orcid.org/0000-0002-6234-8155 https://orcid.org/0000-0002-6153-8803 |
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