RGD Reference Report - Studies on the DIDS-binding site of monocarboxylate transporter 1 suggest a homology model of the open conformation and a plausible translocation cycle. - Rat Genome Database

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Studies on the DIDS-binding site of monocarboxylate transporter 1 suggest a homology model of the open conformation and a plausible translocation cycle.

Authors: Wilson, MC  Meredith, D  Bunnun, C  Sessions, RB  Halestrap, AP 
Citation: Wilson MC, etal., J Biol Chem. 2009 Jul 24;284(30):20011-21. doi: 10.1074/jbc.M109.014217. Epub 2009 May 27.
RGD ID: 7242735
Pubmed: (View Article at PubMed) PMID:19473976
DOI: Full-text: DOI:10.1074/jbc.M109.014217

Site-directed mutagenesis of MCT1 was performed on exofacial lysines Lys(38), Lys(45), Lys(282), and Lys(413). K38Q-MCT1 and K38R-MCT1 were inactive when expressed at the plasma membrane of Xenopus laevis oocytes, whereas K45R/K282R/K413R-MCT1 and K45Q/K282Q/K413Q-MCT1 were active. The former exhibited normal reversible and irreversible inhibition by DIDS, whereas the latter showed less reversible and no irreversible inhibition. K45Q/K413Q-MCT1 retained some irreversible inhibition, whereas K45Q/K282Q-MCT1 and K282Q/K413Q-MCT1 did not. These data suggest that the two DIDS SO(3)(-) groups interact with positively charged Lys(282) together with Lys(45) and/or Lys(413). This positions one DIDS isothiocyanate group close to Lys(38), leading to its covalent modification and irreversible inhibition. Additional mutagenesis revealed that DIDS cross-links MCT1 to its ancillary protein embigin using either Lys(38) or Lys(290) of MCT1 and Lys(160) or Lys(164) of embigin. We have modeled a possible structure for the outward facing (open) conformation of MCT1 by employing modest rotations of the C-terminal domain of the inner facing conformation modeled previously. The resulting model structure has a DIDS-binding site consistent with experimental data and locates Lys(38) in a hydrophobic environment at the bottom of a substrate-binding channel. Our model suggests a translocation cycle in which Lys(38) accepts a proton before binding lactate. Both the lactate and proton are then passed through the channel via Asp(302-) and Asp(306+), an ion pair already identified as important for transport and located adjacent to Phe(360), which controls channel selectivity. The cross-linking data have also been used to model a structure of MCT1 bound to embigin that is consistent with published data.

Annotation

Gene Ontology Annotations    

Biological Process

Cellular Component

Molecular Function

Objects Annotated

Genes (Rattus norvegicus)
Slc16a1  (solute carrier family 16 member 1)

Objects referenced in this article
Gene Emb embigin Rattus norvegicus
Gene Pth parathyroid hormone Rattus norvegicus

Additional Information