Fig 1.
Structures of horse cyt c and PA cyt c551.
Horse cyt c (upper left) and PA cyt c551 (upper right). The hemes and axial ligands are shown as stick models. The heme, the sulfur atoms of the heme axial Met ligand and heme-linked Cys, and the nitrogen atoms of the heme axial His ligand are shown in gray, yellow, and blue, respectively. The secondary structure diagrams of horse cyt c and PA cyt c551 are depicted at the bottom of the figure. The helices are depicted as arrows in the secondary structure diagrams. The helices and loops are labeled as H1–H4 and L1–L3, respectively.
Table 1.
Regions of secondary structures of horse cyt c and PA cyt c551.
Fig 2.
Crystal structures of monomeric and dimeric WT PA cyt c551.
(A) Structure of monomeric WT PA cyt c551 (PDB ID: 351C). (B) Structure of dimeric WT PA cyt c551 solved in this study (pink and cyan, PDB ID: 3X39). The two protomers are depicted in pink and cyan, respectively. The hemes, Cys12, Cys15, His16, and Met61 are shown as stick models. The N- and C-termini are labeled as N and C, respectively. The hemes and Thr20–Met22 residues (hinge loop) are depicted in dark and pale colors, respectively. The sulfur atoms of the heme axial Met ligand and heme-linked Cys are shown in yellow, and the nitrogen atoms of the heme axial His ligand are shown in blue.
Fig 3.
Active site structures of monomeric and dimeric WT PA cyt c551.
(A) Structure of monomeric WT PA cyt c551 (PDB ID: 351C). (B) Structure of dimeric WT PA cyt c551 (PDB ID: 3X39). The heme and side-chains of amino acid residues near the heme (Phe7, Cys12, Ala14, Cys15, His16, Val23, Pro25, Val30, Leu44, Arg47, Ile48, Ser52, Trp56, Pro60, Met61, Pro62, Pro63, Asn64, Leu74, and Val78) are shown as stick models. The sulfur atoms of the heme axial Met ligand and heme-linked Cys are shown in yellow, and the nitrogen atoms of the heme axial His ligand are shown in blue. The cyan strand in the dimeric structure is a region from another molecule. The hemes and Thr20–Met22 residues (hinge loop) are depicted in dark and pale colors, respectively.
Table 2.
Fe–His16 and Fe–Met61 distances in monomeric and dimeric WT PA cyt c551.
Fig 4.
CD spectra and small angle X-ray scattering curves of WT and M61A PA cyt c551.
(A) CD spectra of oxidized monomeric WT (red) and M61A (green) PA cyt c551. Measurement conditions: Sample concentration, 10 μM (heme unit); buffer, 50 mM potassium phosphate buffer; pH, 7.0; temperature, room temperature. (B) Small angle X-ray scattering curves of oxidized monomeric WT (red) and M61A (green) PA cyt c551 shown by Kratky plots. The intensities are normalized at their maximum intensities. Measurement conditions: sample concentration, 500 μM (heme unit); buffer, 50 mM potassium phosphate buffer; pH, 7.0; temperature, 20°C.
Fig 5.
Topology diagrams of PA cyt c551 and horse cyt c.
(A) Monomeric PA cyt c551, (B) dimeric PA cyt c551, (C) monomeric horse cyt c, and (D) dimeric horse cyt c. The helices and loops are labeled as H1–H4 and L1–L3, respectively. The helices are depicted as arrows. The hinge loops in the monomers are depicted in pink.