Family of Cytochromec₇-Type Proteins fromGeobacter sulfurreducens:  Structure of One Cytochromec₇at 1.45 Å Resolution^,

Abstract

The structure of a cytochrome c(7) (PpcA) from Geobacter sulfurreducens was determined by X-ray diffraction at 1.45 A resolution; the R factor is 18.2%. The protein contains a three-heme core that is surrounded by 71 amino acid residues. An unusual feature of this cytochrome is that it has 17 lysine residues, but only nine hydrophobic residues that are larger than alanine. The details of the structure are described and compared with those of cytochrome c(7) from Desulfuromonas acetoxidans and with cytochromes c(3). The two cytochrome c(7) molecules have sequences that are 46% identical, but the arrangements of the hemes in the two structures differ; the rms deviation of all alpha-carbons is 2.5 A. These cytochromes can reduce various metal ions. The reduction site of the chromate ion in D. acetoxidans is occupied by a sulfate ion in the crystal structure of PpcA. We identified four additional homologues of cytochrome c(7) in the G. sulfurreducens genome and three polymers of c(7)-type domains. Of the polymers, two have four repeats and one has nine repeats. On the basis of sequence alignments, one of the hemes in each of the cytochrome c(7)-type domains does not have the bis-histidine coordination. The packing of the molecules in the crystal structure of PpcA suggests that the polymers have an elongated conformation and might form a "nanowire".

Orientation of the axial ligands and magnetic properties of the hemes in the triheme ferricytochrome PpcA from G. sulfurreducens determined by paramagnetic NMR

“…1 Supplementary data) and thus that the model can be applied. Table 2 Comparison between the molecular orbital parameters obtained by fitting the 13 C signals of the a-substituents of the heme and the geometry of the axial ligands reported in the X-ray structure [8]. The parameter b was calculated from the energy splitting of the molecular orbitals [17].…”

Backbone, side chain and heme resonance assignments of the triheme cytochrome PpcA from Geobacter sulfurreducens

“…In fact, in addition to the usual location in the inner membrane and periplasmic space, multiheme cytochromes have been identified in Gs' outer membrane (Mehta et al 2005). Also, an unusual periplasmic pool of five triheme cytochromes was identified in Gs (Pokkuluri et al 2004). PpcA is the most abundant of these cytochromes and gene knock-out experiments have demonstrated its role in extracellular reduction of Fe(III) and U(VI) oxides (Shelobolina et al 2007).…”

“…Using this expression system, 15 N-labeled PpcA was obtained, and its NMR solution structure is currently in progress. This protein has a MW of 9.57 kDa, contains three low spin c-type heme groups with bis-histidinyl axial coordination and has a unusual high content (24%) of lysine residues (Pokkuluri et al 2004). Because the number of structural restraints associated with the heme signals are in average four times higher than those involving any protein residue, their assignment is critical to the accomplishment of a highresolution structure.…”

Effective Variations of related Physicochemical Properties of Nucleotides Leading to Amino Acids for Characterizing Genes and Proteins

“…Periplasmic c7 type cytochrome A (PpcA) protein is determined in Geobacter sulfur reducens along with its other four homologs (PpcB-E). From the crystal structure view point the observation emerges that PpcA protein can bind with Deoxycholate (DXCA) [20][21], while its other homologs do not. DNA sequences of PPCA, PPCB, PPCC, PPCD and PPCE are taken from NCBI gene bank.…”