Hemes on a string: insights on the functional mechanisms of PgcA from Geobacter sulfurreducens

Fernandes, TM, Silva MA, Morgado L, Salgueiro CA.  2023.  Hemes on a string: insights on the functional mechanisms of PgcA from Geobacter sulfurreducens. Journal of Biological Chemistry. :105167.


Microbial extracellular reduction of insoluble compounds requires soluble electron shuttles that diffuse in the extracellular environment, freely diffusing cytochromes or direct contact with cellular conductive appendages that release or harvest electrons to assure a continuous balance between cellular requirements and environmental conditions. In this work, we produced and characterized the three cytochrome domains of PgcA, an extracellular triheme cytochrome that contributes to Fe(III) and Mn(IV) oxides reduction in Geobacter sulfurreducens. The three domains are structurally homologous, but their heme groups show variable axial coordination and reduction potential values. Electron transfer experiments monitored by NMR and visible spectroscopy show the variable extent to which the domains promiscuously exchange electrons, while reducing different electron acceptors. The results suggest that PgcA is part of a new class of cytochromes - microbial heme-tethered redox strings - that use low-complexity protein stretches to bind metals and promote intra- and intermolecular electron transfer events through its cytochrome domains.



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