Protein-protein interaction regulates the direction of catalysis and electron transfer in a redox enzyme complex.

Protein-protein interactions are well-known to regulate enzyme activity in cell signaling and metabolism. Here, we show that protein-protein interactions regulate the activity of a respiratory-chain enzyme, CymA, by changing the direction or bias of catalysis. CymA, a member of the widespread NapC/NirT superfamily, is a menaquinol-7 (MQ-7) dehydrogenase that donates electrons to several distinct terminal reductases in the versatile respiratory network of Shewanella oneidensis .

Multi-heme proteins: nature's electronic multi-purpose tool.

While iron is often a limiting nutrient to Biology, when the element is found in the form of heme cofactors (iron protoporphyrin IX), living systems have excelled at modifying and tailoring the chemistry of the metal. In the context of proteins and enzymes, heme cofactors are increasingly found in stoichiometries greater than one, where a single protein macromolecule contains more than one heme unit. When paired or coupled together, these protein associated heme groups perform a wide variety of tasks, such as redox communication, long range electron transfer and storage of reducing/oxidizing equivalents.

Mind the gap: diversity and reactivity relationships among multihaem cytochromes of the MtrA/DmsE family.

Shewanella oneidensis MR-1 has the ability to use many external terminal electron acceptors during anaerobic respiration, such as DMSO. The pathway that facilitates this electron transfer includes the decahaem cytochrome DmsE, a paralogue of the MtrA family of decahaem cytochromes. Although both DmsE and MtrA are decahaem cytochromes implicated in the long-range electron transfer across a ~300 Å (1 Å=0.

Solution-based structural analysis of the decaheme cytochrome, MtrA, by small-angle X-ray scattering and analytical ultracentrifugation.

The potential exploitation of metal-reducing bacteria as a means for environmental cleanup or alternative fuel is an exciting prospect; however, the cellular processes that would allow for these applications need to be better understood. MtrA is a periplasmic decaheme c-type cytochrome from Shewanella oneidensis involved in the reduction of extracellular iron oxides and therefore is a critical element in Shewanella ability to engage in extracellular charge transfer. As a relatively small 333-residue protein, the heme content is surprisingly high.

Tools for resolving complexity in the electron transfer networks of multiheme cytochromes c.

Examining electron transfer between two proteins with identical spectroscopic signatures is a challenging task. It is supposed that several multiheme cytochromes in Shewanella oneidensis form a molecular "wire" through which electrons are transported across the cellular space and a direct study of this transient protein-protein interaction has not yet been reported. In this study, we present variations on catalytic protein film voltammetry and an anaerobic affinity chromatography assay to demonstrate unidirectional electron transfer between proposed protein pairs.