Transmembrane Domain 1 of Human Organic Anion Transporting Polypeptide 2B1 Is Essential for Transporter Function and Stability

Abstract

Organic anion transporting polypeptides (OATPs, gene symbol ) are important membrane transporter proteins that mediate the uptake of wide ranges of endogenous and exogenous compounds. OATP2B1 has been found in multiple organs and tissues, including the liver, small intestine, kidney, brain, placenta, heart, skin, as well as skeletal muscle, and is proposed to be involved in the uptake of orally administered drugs. Quite a few reports have demonstrated that transmembrane domains (TMs) are crucial for proper functions of OATP family members. Comparative modeling proposed that TM1, along with TM2, 4, and 5 of the N-terminal half of OATP2B1, may be localized within the substrate interaction pocket and are important for uptake function of the transporter. Alanine scanning of the putative transmembrane domain 1 of OATP2B1 revealed that substitution of L58 with alanine dramatically altered the K value, and mutation of V52, H55, Q59, and L69 resulted in significantly reduced substrate turnover number, whereas A61V, Q62A, and S66A exhibited significant change in both K and V values. In addition, phenylalanine at position 51 seems to play an important role in maintaining proper folding of OATP2B1 because alanine replacement of F51 caused accelerated degradation of the transporter protein. Although proteasome and lysosome inhibitors could partially recover protein level, the mutant transporter remained nonfunctional. Taken together, the identification of nine essential amino acid residues within TM1 of OATP2B1 suggested that the transmembrane domain is important for maintaining proper function of the transporter.

Data-Driven Ensemble Docking to Map Molecular Interactions of Steroid Analogs with Hepatic Organic Anion Transporting Polypeptides

“…Whereas the carbonyl oxygen at position R-17 position typically forms the H-bond interaction with the GLN196 side chain, H-bond formation between the phosphono group at either R-2 or R-4 position is typically formed with SER66 (or sometimes also with the neighboring GLN62; see Figures and S14). SER66 was reported in literature to be important for transport of endogenous substrates, and it is interesting that this residue is located at the corresponding position 45 in OATP1B1 and OATP1B3 (which seems to be important for differences in binding in these other two transporters; see previous chapter). Also, GLN62 is an experimentally confirmed functionally important residue in OATP2B1 …”

“…SER66 was reported in literature to be important for transport of endogenous substrates, and it is interesting that this residue is located at the corresponding position 45 in OATP1B1 and OATP1B3 (which seems to be important for differences in binding in these other two transporters; see previous chapter). Also, GLN62 is an experimentally confirmed functionally important residue in OATP2B1 …”

Gly45 and Phe555 in Transmembrane Domains 1 and 10 Are Critical for the Activation of Organic Anion Transporting Polypeptide 1B3 by Epigallocatechin Gallate

“…A recent study showed that TM1 is important for maintaining proper function of OATP2B1 . However, no study examining the role of TM1 for the function of OATP1B3 has been reported thus far.…”

Thyroid Hormone Transporters

“…Several groups have strived to identify the substrate-interacting residues and delineate the transport translocation mechanism of OATPs. However, most of these studies focused on transporters other than OATP1C1 or substrates other than iodothyronines (282)(283)(284)(285)(286)(287)(288)(289)(290)(291)(292)(293)(294). Therefore, it is unclear to what extent these findings also apply to the transport of iodothyronines.…”