Residues in the eighth transmembrane domain of the proton-coupled folate transporter (SLC46A1) play an important role in defining the aqueous translocation pathway and in folate substrate binding

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Abstract

The proton-coupled folate transporter (PCFT-SLC46A1) is required for intestinal folate absorption and folate transport across the choroid plexus. This report addresses the structure/function of the 8th transmembrane helix. Based upon biotinylation of cysteine-substituted residues by MTSEA-biotin, 14 contiguous exofacial residues to Leu316 were accessible to the extracellular compartment of the 23 residues in this helix (Leu303-Leu325). Pemetrexed blocked biotinylation of six Cys-substituted residues deep within the helix implicating an important role for this region in folate binding. Accessibility decreased at 4 °C vs RT. The influx Kt, Ki and Vmax were markedly increased for the P314C mutant, similar to what was observed for Y315A and Y315P mutants. However, the Kt, alone, was increased for the P314Y mutant. To correlate these observations with PCFT structural changes during the transport cycle, homology models were built for PCFT based upon the recently reported structures of bovine and rodent GLUT5 fructose transporters in the inward-open and outward- open conformations, respectively. The models predict substantial structural alterations in the exofacial region of the eighth transmembrane helix as it cycles between its conformational states that can account for the extended and contiguous aqueous accessibility of this region of the helix. Further, a helix break in one of the two conformations can account for the critical roles Pro314 and Tyr315, located in this region, play in PCFT function. The data indicates that the 8th transmembrane helix of PCFT plays an important role in defining the aqueous channel and the folate binding pocket.

Original languageEnglish (US)
Pages (from-to)2193-2202
Number of pages10
JournalBiochimica et Biophysica Acta - Biomembranes
Volume1859
Issue number11
DOIs
StatePublished - Nov 1 2017

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Proton-Coupled Folate Transporter
Folic Acid
Biotinylation
Substrates
Pemetrexed
Conformations
Choroid Plexus
Intestinal Absorption
Fructose
Cysteine
Rodentia

Keywords

  • Folate
  • Homology modeling
  • Membrane transport
  • Slc46A1
  • Transmembrane domain
  • Transporter

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

Cite this

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title = "Residues in the eighth transmembrane domain of the proton-coupled folate transporter (SLC46A1) play an important role in defining the aqueous translocation pathway and in folate substrate binding",
abstract = "The proton-coupled folate transporter (PCFT-SLC46A1) is required for intestinal folate absorption and folate transport across the choroid plexus. This report addresses the structure/function of the 8th transmembrane helix. Based upon biotinylation of cysteine-substituted residues by MTSEA-biotin, 14 contiguous exofacial residues to Leu316 were accessible to the extracellular compartment of the 23 residues in this helix (Leu303-Leu325). Pemetrexed blocked biotinylation of six Cys-substituted residues deep within the helix implicating an important role for this region in folate binding. Accessibility decreased at 4 °C vs RT. The influx Kt, Ki and Vmax were markedly increased for the P314C mutant, similar to what was observed for Y315A and Y315P mutants. However, the Kt, alone, was increased for the P314Y mutant. To correlate these observations with PCFT structural changes during the transport cycle, homology models were built for PCFT based upon the recently reported structures of bovine and rodent GLUT5 fructose transporters in the inward-open and outward- open conformations, respectively. The models predict substantial structural alterations in the exofacial region of the eighth transmembrane helix as it cycles between its conformational states that can account for the extended and contiguous aqueous accessibility of this region of the helix. Further, a helix break in one of the two conformations can account for the critical roles Pro314 and Tyr315, located in this region, play in PCFT function. The data indicates that the 8th transmembrane helix of PCFT plays an important role in defining the aqueous channel and the folate binding pocket.",
keywords = "Folate, Homology modeling, Membrane transport, Slc46A1, Transmembrane domain, Transporter",
author = "Srinivas Aluri and Rongbao Zhao and Andras Fiser and Goldman, {I. David}",
year = "2017",
month = "11",
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doi = "10.1016/j.bbamem.2017.08.006",
language = "English (US)",
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pages = "2193--2202",
journal = "Biochimica et Biophysica Acta - Biomembranes",
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TY - JOUR

T1 - Residues in the eighth transmembrane domain of the proton-coupled folate transporter (SLC46A1) play an important role in defining the aqueous translocation pathway and in folate substrate binding

AU - Aluri, Srinivas

AU - Zhao, Rongbao

AU - Fiser, Andras

AU - Goldman, I. David

PY - 2017/11/1

Y1 - 2017/11/1

N2 - The proton-coupled folate transporter (PCFT-SLC46A1) is required for intestinal folate absorption and folate transport across the choroid plexus. This report addresses the structure/function of the 8th transmembrane helix. Based upon biotinylation of cysteine-substituted residues by MTSEA-biotin, 14 contiguous exofacial residues to Leu316 were accessible to the extracellular compartment of the 23 residues in this helix (Leu303-Leu325). Pemetrexed blocked biotinylation of six Cys-substituted residues deep within the helix implicating an important role for this region in folate binding. Accessibility decreased at 4 °C vs RT. The influx Kt, Ki and Vmax were markedly increased for the P314C mutant, similar to what was observed for Y315A and Y315P mutants. However, the Kt, alone, was increased for the P314Y mutant. To correlate these observations with PCFT structural changes during the transport cycle, homology models were built for PCFT based upon the recently reported structures of bovine and rodent GLUT5 fructose transporters in the inward-open and outward- open conformations, respectively. The models predict substantial structural alterations in the exofacial region of the eighth transmembrane helix as it cycles between its conformational states that can account for the extended and contiguous aqueous accessibility of this region of the helix. Further, a helix break in one of the two conformations can account for the critical roles Pro314 and Tyr315, located in this region, play in PCFT function. The data indicates that the 8th transmembrane helix of PCFT plays an important role in defining the aqueous channel and the folate binding pocket.

AB - The proton-coupled folate transporter (PCFT-SLC46A1) is required for intestinal folate absorption and folate transport across the choroid plexus. This report addresses the structure/function of the 8th transmembrane helix. Based upon biotinylation of cysteine-substituted residues by MTSEA-biotin, 14 contiguous exofacial residues to Leu316 were accessible to the extracellular compartment of the 23 residues in this helix (Leu303-Leu325). Pemetrexed blocked biotinylation of six Cys-substituted residues deep within the helix implicating an important role for this region in folate binding. Accessibility decreased at 4 °C vs RT. The influx Kt, Ki and Vmax were markedly increased for the P314C mutant, similar to what was observed for Y315A and Y315P mutants. However, the Kt, alone, was increased for the P314Y mutant. To correlate these observations with PCFT structural changes during the transport cycle, homology models were built for PCFT based upon the recently reported structures of bovine and rodent GLUT5 fructose transporters in the inward-open and outward- open conformations, respectively. The models predict substantial structural alterations in the exofacial region of the eighth transmembrane helix as it cycles between its conformational states that can account for the extended and contiguous aqueous accessibility of this region of the helix. Further, a helix break in one of the two conformations can account for the critical roles Pro314 and Tyr315, located in this region, play in PCFT function. The data indicates that the 8th transmembrane helix of PCFT plays an important role in defining the aqueous channel and the folate binding pocket.

KW - Folate

KW - Homology modeling

KW - Membrane transport

KW - Slc46A1

KW - Transmembrane domain

KW - Transporter

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DO - 10.1016/j.bbamem.2017.08.006

M3 - Article

C2 - 28802835

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VL - 1859

SP - 2193

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JO - Biochimica et Biophysica Acta - Biomembranes

JF - Biochimica et Biophysica Acta - Biomembranes

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