Multiple Roles of Charged Amino Acids in Cytoplasmic Loop 7 for Expression and Function of the Multidrug and Organic Anion Transporter MRP1 (ABCC1)

The human SLC22A6/OAT1 plays an important role in the disposition of a broad range of endogenous substances and xenobiotics. This is particularly important from the pharmacological point of view since OAT1 is involved in drug elimination events. Furthermore, OAT1 is also involved in key physiological events such as the remote inter-organ communication. Despite its significance, the knowledge about OAT1 structure and the transport mechanism at the atomic level remains fragmented owing to the lack of resolved structures. By means of protein-threading modeling refined by μs-scaled Molecular Dynamics simulations, the present study provides the first robust model of hOAT1 in outward-facing conformation. Taking advantage of the AlphaFold 2 predicted structure of hOAT1 in inward-facing conformation, we here provide the essential structural and functional features comparing both states. The intracellular motifs conserved among Major Facilitator Superfamily members create a so-called "charge-relay system" that works as molecular switches modulating the conformation. The principal element of the event points at interactions charged residues that appear crucial for the transporter dynamics and function. Besides, hOAT1 model was embedded in different lipid bilayer membranes highlighting the crucial structural dependence on lipid-protein. MD simulations supported the pivotal role of phosphatidylethanolamine (PE) components on the protein conformation stability. The present model is made available to decipher the impact of any observed polymorphism and mutation on drug transport as well as to understand substrate binding modes.

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Molecular characterization of human and rat organic anion transporter OATP-D

AJP Renal Physiology ◽

10.1152/ajprenal.00402.2002 ◽

2003 ◽

Vol 285 (6) ◽

pp. F1188-F1197 ◽

Cited By ~ 54

Author(s):

Hisanobu Adachi ◽

Takehiro Suzuki ◽

Michiaki Abe ◽

Naoki Asano ◽

Hiroya Mizutamari ◽

...

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Amino Acid Sequence ◽

Sequence Homology ◽

Organic Anion ◽

Organic Anion Transporter ◽

Prostaglandin E ◽

Amino Acid Sequence Homology ◽

Phylogenetic Tree Analysis ◽

Anion Transporter

We have isolated and characterized a novel human and rat organic anion transporter subtype, OATP-D. The isolated cDNA from human brain encodes a polypeptide of 710 amino acids ( Mr 76,534) with 12 predicted transmembrane domains. The rat clone encodes 710 amino acids ( Mr 76,821) with 97.6% amino acid sequence homology with human OATP-D. Human and rat OATP-D have moderate amino acid sequence homology with LST-1/rlst-1, the rat oatp family, the prostaglandin transporter, and moat1/MOAT1/KIAA0880/OATP-B. Phylogenetic tree analysis revealed that OATP-D is branched in a different position from all known organic anion transporters. OATP-D transports prostaglandin E1 ( Km 48.5 nM), prostaglandin E2 ( Km 55.5 nM), and prostaglandin F2α, suggesting that, functionally, OATP-D encodes a protein that has similar characteristics to those of the prostaglandin transporter. Rat OATP-D also transports prostaglandins. The expression pattern of OATP-D mRNA was abundant mainly in the heart, testis, brain, and some cancer cells. Immunohistochemical analysis further revealed that rat OATP-D is widely expressed in the vascular, renal, and reproductive system at the protein level. These results suggest that OATP-D plays an important role in translocating prostaglandins in specialized tissues and cells.

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