This ANR-NSF international project (PRCI) is led by Nikhil Malvankar of Yale University and Olivera Francetic of Institut Pasteur.
The aim of the project is to explore the mechanism of assembly and ultrafast electron transport and storage in microbial biofilms via cytochrome nanowires.
The specific goal of the IP team is to reconstitute assembly of unusual type IV pilin subunits PilAN-C composed of two interacting polypeptides, which are in turn assembled into pili via so far unidentified assembly factors. We hypothesise that PilAN-C endopili promote secretion of cytochromes which build extracellular nanowires. Typically, cofactor-containing proteins, including the heme-binding cytochromes, must be secreted in a folded state. Type II secretion systems (T2SS), such as the Klebsiella T2SS studies in the Francetic team, are dedicated to the folded protein secretion. In the soil Gram-negative bacteria such as Geobacter, cytochrome secretion apparatus appears to represent a novel type of a secretion system with elements of T2SS, but also type IV pili (T4P). Pilin subunits PilAN and PilAC are encoded in a T4P gene cluster and regulated by a PilR/S twp-component system. By combining genetic reconstitution and interaction analysis we aim to define all essential elements of this novel hybrid type IV filament assembly system.