Multi-heme proteins such as STC or MtrF are membrane proteins facilitating long-range electron transfer (ET) across cell membrane in metal-reducing bacteria [1]. We used classical molecular dynamics (MD) together with electronic-structure calculations based on density functional theory (DFT) to show that in native environment the conducted electrons are transferred by incoherent hopping between the heme cofactors. Kinetics of the ET is significantly enhanced by presence of cysteine linkages [2,3,4]. However, recent experimental measurements of current-voltage curves suggested that the ET mechanism changes to coherent electron tunneling in vacuum when the protein is electronically coupled with metal electrodes [5]. Therefore, we performed MD simulations in accurate gold/protein interaction force field [6] to identify adsorption of STC and MtrF between two gold electrodes. By the large-scale DFT calculation on the complete interfacial structure with state-of-the-art band alignment corrections we were able to identify the conduction channels in the STC junction. These are formed predominantly by delocalized heme iron states. Finally, we applied Landauer formalism to compute I-V curves on investigated junctions using the DFT electronic states corrected for band alignment and the ET mechanism is discussed.