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The multi-heme, outer membrane c-type cytochrome ( c- Cyt) OmcB of G eobacter sulfurreducens was previously proposed to mediate electron transfer across the outer membrane. However, the underlying mechanism has remained uncharacterized. In G . sulfurreducens, the omcB gene is part of two tandem four-gene clusters, each is predicted to encode a transcriptional factor ( OrfR/ OrfS), a porin-like outer membrane protein ( OmbB/ OmbC), a periplasmic c-type cytochrome ( OmaB/ OmaC) and an outer membrane c- Cyt ( OmcB/ OmcC) respectively. Here, we showed that OmbB/ OmbC, OmaB/ OmaC and OmcB/ OmcC of G . sulfurreducens PCA formed the porin-cytochrome ( Pcc) protein complexes, which were involved in transferring electrons across the outer membrane. The isolated Pcc protein complexes reconstituted in proteoliposomes transferred electrons from reduced methyl viologen across the lipid bilayer of liposomes to Fe( III)-citrate and ferrihydrite. The pcc clusters were found in all eight sequenced G eobacter and 11 other bacterial genomes from six different phyla, demonstrating a widespread distribution of Pcc protein complexes in phylogenetically diverse bacteria. Deletion of ombB-omaB-omcB-orfS-ombC-omaC-omcC gene clusters had no impact on the growth of G . sulfurreducens PCA with fumarate but diminished the ability of G . sulfurreducens PCA to reduce Fe( III)-citrate and ferrihydrite. Complementation with the ombB-omaB-omcB gene cluster restored the ability of G . sulfurreducens PCA to reduce Fe( III)-citrate and ferrihydrite. [ABSTRACT FROM AUTHOR]

Crystals of a complex formed between the 59 kDa N-terminal fragment of the Escherichia coli DNA gyrase A subunit (also known as the breakage-reunion domain) and the antibiotic simocyclinone D8 were grown by vapour diffusion. The complex crystallized with I-centred orthorhombic symmetry and X-ray data were recorded to a resolution of 2.75 Å from a single crystal at the synchrotron. DNA gyrase is an essential bacterial enzyme and thus represents an attractive target for drug development. [ABSTRACT FROM AUTHOR]

Decades of research describe myriad redox enzymes that contain cofactors arranged in tightly packed chains facilitating rapid and controlled intra-protein electron transfer. Many such enzymes participate in extracellular electron transfer (EET), a process which allows microorganisms to conserve energy in anoxic environments by exploiting mineral oxides and other extracellular substrates as terminal electron acceptors. In this work, we describe the properties of the triheme cytochrome PgcA from Geobacter sulfurreducens. PgcA has been shown to play an important role in EET but is unusual in containing three CXXCH heme binding motifs that are separated by repeated (PT) x motifs, suggested to enhance binding to mineral surfaces. Using a combination of structural, electrochemical, and biophysical techniques, we experimentally demonstrate that PgcA adopts numerous conformations stretching as far as 180 Å between the ends of domains I and III, without a tightly packed cofactor chain. Furthermore, we demonstrate a distinct role for its domain III as a mineral reductase that is recharged by domains I and II. These findings show PgcA to be the first of a new class of electron transfer proteins, with redox centers separated by some nanometers but tethered together by flexible linkers, facilitating electron transfer through a tethered diffusion mechanism rather than a fixed, closely packed electron transfer chain., (© 2024 The Author(s). Protein Science published by Wiley Periodicals LLC on behalf of The Protein Society.)

Heme containing proteins are involved in a broad range of cellular functions, from oxygen sensing and transport to catalyzing oxidoreductive reactions. The two major types of cytochrome (b-type and c-type) only differ in their mechanism of heme attachment, but this has major implications for their cellular roles in both localization and mechanism. The b-type cytochromes are commonly cytoplasmic, or are within the cytoplasmic membrane, while c-type cytochromes are always found outside of the cytoplasm. The mechanism of heme attachment allows for complex c-type multiheme complexes, having the capacity to hold multiple electrons, to be assembled. These are increasingly being identified as secreted into the extracellular environment. For organisms that respire using extracellular substrates, these large multiheme cytochromes allow for electron transfer networks from the cytoplasmic membrane to the cell exterior for the reduction of extracellular electron acceptors. In this review the structures and functions of these networks and the mechanisms by which electrons are transferred to extracellular substrates is described., (© 2019 The Authors. Protein Science published by Wiley Periodicals, Inc. on behalf of The Protein Society.)