Substrate binding and lipid-mediated allostery in the human organic anion transporter 1 at the atomic-scale

Abstract

The Organic Anion Transporter 1 is a membrane transporter known for its central role in drug elimination by the kidney. hOAT1 is an antiporter translocating substrate in exchange for -ketoglutarate. The understanding of hOAT1 structure and function remains limited due to the absence of resolved structure of hOAT1. Benefiting from conserved structural and functional patterns shared with other Major Facilitator Superfamily transporters, the present study intended to investigate fragments of hOAT1 transport function and modulation of its activity in order to make a step forward the understanding of its transport cycle. s-long molecular dynamics simulation of hOAT1 were carried out suggesting two plausible binding sites for a typical substrate, adefovir, in line with experimental observations. The well-known B-like motif binding site was observed in line with previous studies. However, we here propose a new inner binding cavity which is expected to be involved in substrate translocation event. Binding modes of hOAT1 co-substrate -ketoglutarate were also investigated suggesting that it may binds to highly conserved intracellular motifs. We here hypothesize that -ketoglutarate may disrupt the pseudo-symmetrical intracellular charge-relay system which in turn may participate to the destabilisation of OF conformation. Investigations regarding allosteric communications along hOAT1 also suggest that substrate binding event might modulate the dynamics of intracellular charge relay system, assisted by surrounding lipids as active partners. We here proposed a structural rationalisation of transport impairments observed for two single nucleotide polymorphisms, p.Arg50His and p.Arg454Gln suggesting that the present model may be used to transport dysfunctions arising from hOAT1 mutations. HighlightsO_LIAdefovir has at least two binding pockets on hOAT1 in the outward-facing conformation. C_LIO_LIThe highly conserved B-motif within MFS is strongly involved in substrate binding. C_LIO_LI-Ketoglutarate binds to the intracellular domain of hOAT1 and destabilizes its OF conformation. C_LIO_LIThe lipid membrane bilayer plays an active role in the allosteric communication between intracellular and extracellular domains of hOAT1. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/500056v2_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@18d092corg.highwire.dtl.DTLVardef@5538e9org.highwire.dtl.DTLVardef@10b62cforg.highwire.dtl.DTLVardef@84421e_HPS_FORMAT_FIGEXP M_FIG The present work (from left): (i) reveals binding modes of adefovir (top) and -ketoglutarate (bottom) to hOAT1; (ii) maps Single Nucleotide Polymorphisms on outward-facing (top) and inward-facing (bottom) conformation of hOAT1; (iii) asses the allosteric effect of lipidic environment and presence of substrates. C_FIG