Dynamical Behavior of the Human Ferroportin Homologue from Bdellovibrio bacteriovorus: Insight into the Ligand Recognition Mechanism.

Valentina Tortosa,Andrea Pasquadibisceglie,Federico Iacovelli,Fabio Polticelli,Mattia Falconi,Maria Carmela Bonaccorsi Di Patti,Giovanni Musci

doi:10.3390/ijms21186785

Abstract

Members of the major facilitator superfamily of transporters (MFS) play an essential role in many physiological processes such as development, neurotransmission, and signaling. Aberrant functions of MFS proteins are associated with several diseases, including cancer, schizophrenia, epilepsy, amyotrophic lateral sclerosis and Alzheimer’s disease. MFS transporters are also involved in multidrug resistance in bacteria and fungi. The structures of most MFS members, especially those of members with significant physiological relevance, are yet to be solved. The lack of structural and functional information impedes our detailed understanding, and thus the pharmacological targeting, of these transporters. To improve our knowledge on the mechanistic principles governing the function of MSF members, molecular dynamics (MD) simulations were performed on the inward-facing and outward-facing crystal structures of the human ferroportin homologue from the Gram-negative bacterium Bdellovibrio bacteriovorus (BdFpn). Several simulations with an excess of iron ions were also performed to explore the relationship between the protein’s dynamics and the ligand recognition mechanism. The results reinforce the existence of the alternating-access mechanism already described for other MFS members. In addition, the reorganization of salt bridges, some of which are conserved in several MFS members, appears to be a key molecular event facilitating the conformational change of the transporter.

Highlights

The major facilitator superfamily (MFS) represents the largest class of secondary active transporters [1,2]; its members are found in bacteria, archaea, and eukarya [3]
The dynamical behavior of BdFpn embedded in a lipid bilayer was studied through molecular dynamics simulations of three different systems: BdFpn in the inward-facing and outward-facing states, to probe the global dynamic behavior of the transporter (Inward_Apo and Outward_Apo, respectively), and BdFpn in the inward-facing state with an excess of iron ions (Inward_Fe), aimed at investigating the encounter of iron with protein residues in the substrate binding pocket, this being the initial event of the ferroportin-mediated iron efflux mechanism
molecular dynamics (MD) simulations of BdFpn allowed us to characterize the conformational dynamics of the protein and to identify key residues involved in the initial encounter with iron and conformational switch of the transporter

Summary

Introduction

The major facilitator superfamily (MFS) represents the largest class of secondary active transporters [1,2]; its members are found in bacteria, archaea, and eukarya [3]. MSF members transport a wide range of substrates, including inorganic anions and cations, amino acids, peptides, monosaccharides, oligosaccharides, enzyme cofactors, toxins, drugs and iron chelates [4]. They operate by uniport, symport, or antiport mechanisms [2]. Two conserved sequences are found at the cytoplasmic ends of TMs 2 and 3 (N-domain) and of TMs 8 and 9 (C-domain) in many MFS members [6] These short connecting segments join the ends of the TM (TM2-TM3; TM8-TM9) allowing better control of relative motions on the cytoplasmic side [6].

Methods

Results

Discussion

Conclusion