| Autor: |
Zacharoff LA; Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN, United States., Morrone DJ; St. Louis College of Pharmacy, St. Louis, MO, United States., Bond DR; Department of Plant and Microbial Biology, University of Minnesota, Minneapolis, MN, United States.; BioTechnology Institute, University of Minnesota, Minneapolis, MN, United States. |
| Abstrakt: |
Extracellular cytochromes are hypothesized to facilitate the final steps of electron transfer between the outer membrane of the metal-reducing bacterium Geobacter sulfurreducens and solid-phase electron acceptors such as metal oxides and electrode surfaces during the course of respiration. The triheme c -type cytochrome PgcA exists in the extracellular space of G. sulfurreducens , and is one of many multiheme c -type cytochromes known to be loosely bound to the bacterial outer surface. Deletion of pgcA using a markerless method resulted in mutants unable to transfer electrons to Fe(III) and Mn(IV) oxides; yet the same mutants maintained the ability to respire to electrode surfaces and soluble Fe(III) citrate. When expressed and purified from Shewanella oneidensis , PgcA demonstrated a primarily alpha helical structure, three bound hemes, and was processed into a shorter 41 kDa form lacking the lipodomain. Purified PgcA bound Fe(III) oxides, but not magnetite, and when PgcA was added to cell suspensions of G. sulfurreducens , PgcA accelerated Fe(III) reduction similar to addition of FMN. Addition of soluble PgcA to Δ pgcA mutants also restored Fe(III) reduction. This report highlights a distinction between proteins involved in extracellular electron transfer to metal oxides and poised electrodes, and suggests a specific role for PgcA in facilitating electron transfer at mineral surfaces. |
