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The binding of platinum hexahalides (Cl, Br and I) to hen egg-white lysozyme and the chemical transformation of the PtI6 octahedral complex to a PtI3 moiety bound to His15.

Tanley SW, Starkey LV, Lamplough L, Kaenket S, Helliwell JR - Acta Crystallogr F Struct Biol Commun (2014)

Bottom Line: This study examines the binding and chemical stability of the platinum hexahalides K2PtCl6, K2PtBr6 and K2PtI6 when soaked into pre-grown hen egg-white lysozyme (HEWL) crystals as the protein host.Each complex does, however, bind to HEWL in its octahedral form either at one site (PtI6) or at two sites (PtBr6 and PtCl6).As heavy-atom derivatives of a protein, the octahedral shape of the hexahalides could be helpful in cases of difficult-to-interpret electron-density maps as they would be recognisable 'objects'.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Chemistry, Faculty of Engineering and Physical Sciences, University of Manchester, Brunswick Street, Manchester M13 9PL, England.

ABSTRACT
This study examines the binding and chemical stability of the platinum hexahalides K2PtCl6, K2PtBr6 and K2PtI6 when soaked into pre-grown hen egg-white lysozyme (HEWL) crystals as the protein host. Direct comparison of the iodo complex with the chloro and bromo complexes shows that the iodo complex is partly chemically transformed to a square-planar PtI3 complex bound to the N(δ) atom of His15, a chemical behaviour that is not exhibited by the chloro or bromo complexes. Each complex does, however, bind to HEWL in its octahedral form either at one site (PtI6) or at two sites (PtBr6 and PtCl6). As heavy-atom derivatives of a protein, the octahedral shape of the hexahalides could be helpful in cases of difficult-to-interpret electron-density maps as they would be recognisable 'objects'.

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PtI6 binding in a special position between two Arg14 residues in symmetry-related molecules. The 2Fo − Fc electron-density map (blue) and the anomalous difference electron-density map (orange) are shown. The Pt atom is in grey and I atoms are in purple.
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fig1: PtI6 binding in a special position between two Arg14 residues in symmetry-related molecules. The 2Fo − Fc electron-density map (blue) and the anomalous difference electron-density map (orange) are shown. The Pt atom is in grey and I atoms are in purple.

Mentions: The binding of PtI6 to HEWL shows both similarities and differences to the previous studies involving PtCl6 (Sun et al., 2002 ▶) and PtBr6 (Helliwell et al., 2010 ▶). PtI6 binds to site 1, a crevice between two Arg14 residues in symmetry-related molecules (Fig. 1 ▶). This site is located at a special position, with a twofold axis passing through the Pt atom and two iodines. Individually refined heavy-atom occupancies, as well as whole group refined occupancies, are given in Supplementary Tables S2–S4 for each hexahalide complex. An octahedral PtI6 molecule is not bound in site 2, a crevice between Ser86, Lys1 and Gln41 of chain A next to Pro79, Asn65 and Asn74 of a symmetry-related molecule. Most interestingly, there is a new binding site that is chemically distinct comprising a PtI3 moiety bound to the Nδ atom of His15, forming a square-planar complex (Fig. 2 ▶).


The binding of platinum hexahalides (Cl, Br and I) to hen egg-white lysozyme and the chemical transformation of the PtI6 octahedral complex to a PtI3 moiety bound to His15.

Tanley SW, Starkey LV, Lamplough L, Kaenket S, Helliwell JR - Acta Crystallogr F Struct Biol Commun (2014)

PtI6 binding in a special position between two Arg14 residues in symmetry-related molecules. The 2Fo − Fc electron-density map (blue) and the anomalous difference electron-density map (orange) are shown. The Pt atom is in grey and I atoms are in purple.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4157407&req=5

fig1: PtI6 binding in a special position between two Arg14 residues in symmetry-related molecules. The 2Fo − Fc electron-density map (blue) and the anomalous difference electron-density map (orange) are shown. The Pt atom is in grey and I atoms are in purple.
Mentions: The binding of PtI6 to HEWL shows both similarities and differences to the previous studies involving PtCl6 (Sun et al., 2002 ▶) and PtBr6 (Helliwell et al., 2010 ▶). PtI6 binds to site 1, a crevice between two Arg14 residues in symmetry-related molecules (Fig. 1 ▶). This site is located at a special position, with a twofold axis passing through the Pt atom and two iodines. Individually refined heavy-atom occupancies, as well as whole group refined occupancies, are given in Supplementary Tables S2–S4 for each hexahalide complex. An octahedral PtI6 molecule is not bound in site 2, a crevice between Ser86, Lys1 and Gln41 of chain A next to Pro79, Asn65 and Asn74 of a symmetry-related molecule. Most interestingly, there is a new binding site that is chemically distinct comprising a PtI3 moiety bound to the Nδ atom of His15, forming a square-planar complex (Fig. 2 ▶).

Bottom Line: This study examines the binding and chemical stability of the platinum hexahalides K2PtCl6, K2PtBr6 and K2PtI6 when soaked into pre-grown hen egg-white lysozyme (HEWL) crystals as the protein host.Each complex does, however, bind to HEWL in its octahedral form either at one site (PtI6) or at two sites (PtBr6 and PtCl6).As heavy-atom derivatives of a protein, the octahedral shape of the hexahalides could be helpful in cases of difficult-to-interpret electron-density maps as they would be recognisable 'objects'.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Chemistry, Faculty of Engineering and Physical Sciences, University of Manchester, Brunswick Street, Manchester M13 9PL, England.

ABSTRACT
This study examines the binding and chemical stability of the platinum hexahalides K2PtCl6, K2PtBr6 and K2PtI6 when soaked into pre-grown hen egg-white lysozyme (HEWL) crystals as the protein host. Direct comparison of the iodo complex with the chloro and bromo complexes shows that the iodo complex is partly chemically transformed to a square-planar PtI3 complex bound to the N(δ) atom of His15, a chemical behaviour that is not exhibited by the chloro or bromo complexes. Each complex does, however, bind to HEWL in its octahedral form either at one site (PtI6) or at two sites (PtBr6 and PtCl6). As heavy-atom derivatives of a protein, the octahedral shape of the hexahalides could be helpful in cases of difficult-to-interpret electron-density maps as they would be recognisable 'objects'.

Show MeSH
Related in: MedlinePlus