Mn(II) binding to human serum albumin: A 1H-NMR relaxometric study

Human serum albumin (HSA) displays several metal binding sites, participating to essential and toxic metal ions disposal and transport. The major Zn(II) binding site, called Site A, is located at the I/II domain interface, with residues His67, Asn99, His247, and Asp249 contributing with five donor atoms to the metal ion coordination. Additionally, one water molecule takes part of the octahedral coordination geometry. The occurrence of the metal-coordinated water molecule allows the investigation of the metal complex geometry by water 1H-NMR relaxation, provided that the diamagnetic Zn(II) is replaced by the paramagnetic Mn(II). Here, the 1H-NMR relaxometric study of Mn(II) binding to HSA is reported. Mn(II) binding to HSA is modulated by Zn(II), pH, and myristate through competitive inhibition and allosteric mechanisms. The body of results indicates that the primary binding site of Zn(II) corresponds to the secondary binding site of Mn(II), i.e. the multimetal binding site A. Excess Zn(II) completely displaces Mn(II) from its primary site suggesting that the primary Mn(II) site corresponds to the secondary Zn(II) site. This uncharacterized site is functionally-linked to FA1; moreover, metal ion binding is modulated by myristate and pH. Noteworthy, water 1H-NMR relaxometry allowed a detailed analysis of thermodynamic properties of HSA–metal ion complexes.

The primary binding site of Zn(II) to HSA corresponds to the secondary binding site of Mn(II), i.e. the multimetal binding site A. Excess Zn(II) completely displaces Mn(II) from its primary site suggesting that the primary Mn(II) site corresponds to the secondary Zn(II) site that is functionally-linked to FA1.Figure optionsDownload as PowerPoint slideHighlights
► Mn(II) binds to two independent sites of HSA.
► Mn(II) binding to its primary site is hampered by myristate and basic pH.
► The secondary Mn(II) binding site corresponds to the primary Zn(II) binding site.