Structural Insights Into The Molecular Mechanism Of Formate Transporter FocA Functioning

FocA is a representative member of the formate-nitrite transporter family, which transports short-chain acids including formate and nitrite in bacteria, archaea, fungi, algae and parasites. The structure and transport mechanism of the formate-nitrite transporter family remain unknown.Here we report the crystal structure of Escherichia coli FocA at 2.25(A|。) resolution. FocA forms a symmetric pentamer, with each protomer consisting of six transmembrane segments. Despite a lack of sequence homology, the overall structure of the FocA protomer closely resembles that of aquaporin and strongly argues that FocA is a channel, rather than a transporter. Structural analysis identifies potentially important channel residues, defines the channel path and reveals two constriction sites. Unlike aquaporin, FocA is impermeable to water but allows the passage of formate.Therefore, a structural, biochemical and biophysical investigation we presented here provides mechanistic insights into the channel activity of FocA and the formate-nitrite transporter family.