Extracellular catalysis of environmental substrates by Shewanella oneidensis MR‐1 occurs via active sites on the C‐terminal domains of MtrC
Alejandro Morales‐Florez, Colin W. J. Lockwood, Benjamin W. Nash, Marcus J. Edwards +4
AI summary
75% confidenceThe study investigates whether the broad substrate specificity of Shewanella oneidensis MR-1's MtrC cytochrome relies on specific binding sites or non-specific interactions near exposed hemes. By engineering a variant containing only domains I and II (MtrCDI,II), researchers aimed to isolate the functional regions responsible for extracellular catalysis.
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Abstract
The Gram‐negative Shewanellaceae family is well known for its ability to transfer catabolically derived electrons to extracellular terminal electron acceptors through electron conduits that permeate the outer membrane. The primary conduit is MtrCAB, a trimeric porin‐cytochrome complex that contains the cell surface exposed decaheme cytochrome MtrC. This donates electrons to extracellular substrates, including OmcA, soluble metals, organic electron shuttles, and insoluble metal oxides. However, it is not clear whether this broad substrate specificity requires specific sites for binding and reduction, or whether reduction occurs through non‐specific interactions near exposed hemes on the cytochrome surface. Shewanella oneidensis MtrC is composed of four domains, with the hemes closely packed and distributed evenly between domains II and IV. The domains are arranged to allow electron transport across the cytochrome via interdomain electron transfer, but the significance of this conserved feature is not understood. Here we use site‐directed mutagenesis to generate an MtrC variant that is comprised only of domains I and II (MtrCDI,II). The properties of this MtrCDI,II are effectively identical to domains I and II of full‐length MtrC. Whole‐cell assays revealed that S. oneidensis cells replacing full‐length MtrC with MtrCDI,II had significantly lower rates of OmcA, flavin mononucleotide, and Fe(III) citrate reduction. Our results demonstrate that MtrC domains III and IV contain sites for association of specific substrates, enabling the reduction of extracellular electron acceptors in S. oneidensis.
Key findings
- The C-terminal domains (III and IV) of MtrC contain the active sites required for reducing diverse extracellular substrates.
- An MtrC variant consisting solely of N-terminal domains I and II retains electron transport capability but lacks significant extracellular catalytic activity.
- Specific structural features within the C-terminal domains are essential for binding and reducing environmental substrates rather than non-specific surface interactions.
Keywords
Identifiers
- PubMed
- 40725986
- Journal
- Protein Science
- Year
- 2025