The crystal structure of Klebsiella pneumoniae FeoA reveals a site for protein‐protein interactions

Abstract

In order to establish infection, pathogenic bacteria must obtain essential nutrients such as iron. Under acidic and/or anaerobic conditions, most bacteria utilize the Feo system in order to acquire ferrous iron (Fe 2+ ) from their host environment. The mechanism of this process, including its regulation, remains poorly understood. In this work, we have determined the crystal structure of FeoA from the nosocomial agent Klebsiella pneumoniae (KpFeoA). Our structure reveals an SH3-like domain that mediates interactions between neighboring polypeptides via hydrophobic intercalations into a Leu-rich surface ridge. Using docking of a small peptide corresponding to a postulated FeoB partner binding site, we demonstrate that KpFeoA can assume both "open" and "closed" conformations, controlled by binding at this Leu-rich ridge. We propose a model in which a "C-shaped" clamp along the FeoA surface mediates interactions with its partner protein, FeoB. These findings are the first to demonstrate atomic-level details of FeoA-based protein-protein interactions and provide a framework for testing FeoA-FeoB interactions, which could be exploited for future antibiotic developments.

Biochemical and structural characterization of the fused Bacteroides fragilis NFeoAB domain reveals a role for FeoA

“…The overall structure of BfFeoA (Fig. 3) is similar to other FeoA proteins that have been determined by NMR or X-ray crystallography (19,20), including the hydrophobic cleft putatively involved in protein-protein interactions, suggesting that the FeoA domain in an FeoAB fusion may function similarly to stand-alone FeoA proteins.…”

“…As visible in Fig. 3A, BfFeoA adopts the β-barrel, SRC Homology 3 (SH3-like) fold that has been observed for other FeoA proteins (19,20,42). The β-barrel is composed of five β-strands, while two α-helices make up the clamp region of BfFeoA, which comprises a series of hydrophobic residues (Phe 23 , Ile 27 , Met 30 , Ile 59 , and Leu 61 ) that we have hypothesized to be important for mediating FeoA-NFeoB interactions (Fig.…”

“…The function of FeoA vis-à-vis FeoB has garnered considerable debate and yet failed to reach a consensus. Given its conserved SH3like fold (19,20,42), which typically mediates protein-protein interactions in other systems, our lab and others have speculated that FeoA may interact with FeoB to alter function. In support of this notion, in vivo studies have demonstrated the ability of FeoA to interact with FeoB in stand-alone tripartite systems (52)(53)(54).…”

“…The β-barrel is composed of five β-strands, while two α-helices make up the clamp region of BfFeoA, which comprises a series of hydrophobic residues (Phe 23 , Ile 27 , Met 30 , Ile 59 , and Leu 61 ) that we have hypothesized to be important for mediating FeoA-NFeoB interactions (Fig. 3B) (20). An additional 3 10 -helix at the beginning of the Nterminus contacts both the final α-helix and βstrand that feed out of and into the hydrophobic clamp, respectively.…”

“…The function of FeoA is unknown, but we do know that FeoA is an ≈ 8 kDa, cytoplasmic β-barrel protein comprising an Src homology 3 (SH3)-like fold, which is commonly involved in protein-protein interactions. Given its structure, FeoA has been hypothesized to interact with FeoB to affect function (2,3,19,20). FeoB is an ≈ 85 kDa transmembrane protein consisting of a G-protein domain, a guanine dissociation inhibitor (GDI) domain, and a transmembrane (TM) domain.…”