Orientation of the axial ligands and magnetic properties of the hemes in the triheme ferricytochrome PpcA from G. sulfurreducens determined by paramagnetic NMR

Abstract

a b s t r a c tThe geometry of the axial ligands of the hemes in the triheme cytochrome PpcA from Geobacter sulfurreducens was determined in solution for the ferric form using the unambiguous assignment of the NMR signals of the a-substituents of the hemes. The paramagnetic 13 C shifts of the hemes can be used to define the heme electronic structure, the geometry of the axial ligands, and the magnetic susceptibility tensor. The latter establishes the magnitude and geometrical dependence of the pseudocontact shifts, which are crucial to warrant reliable structural constraints for a detailed structural characterization of this paramagnetic protein in solution.

Rational engineering of Geobacter sulfurreducens electron transfer components: a foundation for building improved Geobacter-based bioelectrochemical technologies

“…The PpcA family cytochromes contain between 70 and 75 amino acids and three c -type hemes axially co-ordinated by two histidine residues (Pokkuluri et al, 2004b , 2010 ; Morgado et al, 2012b ). The hemes are low spin in both diamagnetic ( S = 0) reduced state and paramagnetic ( S = 1/2) oxidized state (Morgado et al, 2010c ; Dantas et al, 2011 ). These features are convenient in that they provide well-resolved 1 H NMR spectra in both states.…”

“…In contrast, in the oxidized form the unpaired electron of each heme iron exerts significant paramagnetic shifts on the heme signals. Consequently, the same heme signals are differently affected by the paramagnetic centers, have different levels of broadening and are spread over the entire spectral width (Figure 4 ) (Morgado et al, 2010c ; Dantas et al, 2011 ). As illustrated in Figure 4 , the heme methyl signals are typically shifted to higher ppm values as the oxidation of the proteins progresses and, therefore, are ideal candidates to monitor the stepwise oxidation of the individual hemes throughout the different oxidation stages (see Figure 3 ).…”

Examination of abiotic cofactor assembly in photosynthetic biomimetics: site-specific stereoselectivity in the conjugation of a ruthenium(II) tris(bipyridine) photosensitizer to a multi-heme protein

“…The cofactors are c-type hemes, covalently bound in CXXCH amino acids motif and ligated by bis-histidine coordination. The crystal and solution structures of PpcA are known to high resolution (Morgado et al 2012(Morgado et al , 2017Pokkuluri et al 2004), and the redox (Morgado et al 2010a), nuclear magnetic resonance (Morgado et al 2010b), and electron paramagnetic resonance properties (Ponomarenko et al 2018) of each of the hemes are distinguishable and well-characterized.…”

Transcriptomic, Proteomic, and Bioelectrochemical Characterization of an Exoelectrogen Geobacter soli Grown With Different Electron Acceptors

“…Current evidence from studies with G. sulfurreducens has revealed that many c -Cyts play an important role in EET: (1) inner-membrane electron transfer uses at least two different pathways, known as the CbcL- and ImcH-dependent pathways ( Levar et al, 2014 ; Zacharoff et al, 2016 ); (2) electron transfer from inner- to outer-membrane might be mediated by PpcA family (PpcA-PpcE) ( Butler et al, 2010 ; Morgado et al, 2010 ); (3) transferring electrons across the outer-membrane relies on trans-outer membrane porins ( Liu et al, 2015 ); and (4) the terminal electron transfer from outer-membrane to electron acceptor is mediated by OmcS and OmcZ ( Mehta et al, 2005 ; Nevin et al, 2009 ).…”