Nucleation of the iron core occurs at the three-fold channels of horse spleen apoferritin: an EXAFS study on the native and chemically-modified protein.

This study explores how the iron core in horse spleen apoferritin, a protein, begins to form at the protein’s three-fold channels. Use of an x-ray technique revealed that the iron forms a clustered structure within the protein. Changes made to the protein resulted in varied effects, which supports that these iron clusters are located at the three-fold channels of the protein.

Research Methodology

• The researchers used extended X-ray absorbance fine structure (EXAFS) measurements to observe the initial formation of the Fe(III)-apoferritin complex, focusing on a Fe/subunit ratio of 2 in native and modified horse spleen apoferritin.
• Data analysis showed that, in the native protein, the iron forms a protein-bound polynuclear cluster. The researchers further found that a first coordination sphere was made up of 5-6 low-Z atoms such as nitrogen atoms or carboxylate-like ligands, or oxo bridges between the iron atoms.

Chemical Modification Effects

• The researchers chemically modified Cys-126, a protein residue located on the outer surface of the hydrophilic three-fold channels, using two different compounds: p-chloromercuribenzoate (PMB) and phenylmercuric acetate (PMA).
• Their results with PMB-modified protein showed the disappearance of the attribute related to the interaction between iron atoms in the spectrum.
• On the other hand, with PMA-reacted protein, the main differences compared to the native protein were observed at the level of the first coordination sphere.

Key Findings

• This research confirmed the formation of protein-Fe(III)-clusters and was able to locate these sites at the hydrophilic three-fold channels of horse spleen apoferritin.
• The alterations when chemical modifications were introduced further underscored these findings, showcasing altered behaviour and structure different from the native protein.