Transport and transporters in the endoplasmic reticulum

Abstract

Enzyme activities localized in the luminal compartment of the endoplasmic reticulum are integrated into the cellular metabolism by transmembrane fluxes of their substrates, products and/or cofactors. Most compounds involved are bulky, polar or even charged; hence, they cannot be expected to diffuse through lipid bilayers. Accordingly, transport processes investigated so far have been found protein-mediated. The selective and often rate-limiting transport processes greatly influence the activity, kinetic features and substrate specificity of the corresponding luminal enzymes. Therefore, the phenomenological characterization of endoplasmic reticulum transport contributes largely to the understanding of the metabolic functions of this organelle. Attempts to identify the transporter proteins have only been successful in a few cases, but recent development in molecular biology promises a better progress in this field.

Impaired O-Linked N-Acetylglucosaminylation in the Endoplasmic Reticulum by Mutated Epidermal Growth Factor (EGF) Domain-specific O-Linked N-Acetylglucosamine Transferase Found in Adams-Oliver Syndrome

“…Nucleotide sugars are transported from the cytosol to the ER and the Golgi by the nucleotide-sugar transporters, highly conserved hydrophobic proteins with multiple transmembrane domains that are part of the solute carrier family 35 (SLC35) (38,39). Of these, SLC35A3 (40 -42) and SLC35D2 (43,44) are reported to be Golgi-resident UDP-GlcNAc transporters.…”

The translocon and the non-specific transport of small molecules in the endoplasmic reticulum (Review)

“…pyridine nucleotides, FAD, etc.). Several transport processes across the ER membrane were proven or hypothesized to be based on antiport mechanism (for a review see Csala et al 2007), which require the appropriate counter-molecules, potentially provided by the slow flux through the translocon. The large amount of evidence supporting the role of translocon in transmembrane fluxes is partially provided by studies in which puromycin or related agents were applied to open the channel.…”

An overview of trafficking and assembly of neurotransmitter receptors and ion channels (Review)

“…Work on metabotropic glutamate receptors in the ER and nuclear envelope of striatal neurons suggests that glutamate can enter the ER via cystineglutamate exchanger and other secondary active transporters [77]. Gating motions of glutamate receptors in the ER [78] might come as a surprise but are consistent with the picture of the ER as a metabolic compartment [79] studded with transport proteins running on coupled gradients [80]. It is now clear that this transport activity provides small molecules that perform the function of pharmacological chaperones to support the biogenesis of ligand-binding membrane proteins.…”