The Effects of N-linked Glycosylation on SLC6 Transporters

Abstract

Membrane transporters of the solute carrier 6 (SLC6) family mediate various physiological processes by facilitating the translocation of amino acids, neurotransmitters, and other metabolites. In the human body, these transporters are tightly controlled through various post-translational modifications with implications on protein expression, stability, membrane trafficking, and dynamics. While N-linked glycosylation is a universal regulatory mechanism among eukaryotes, the exact molecular mechanism of how glycosylation affects the SLC6 transporter family. It is generally believed that glycans influence transporter stability and membrane trafficking, however, the role of glycosylation on transporter dynamics remains inconsistent, with differing conclusions among individual transporters across the SLC6 family. In this study, we collected over 1 millisecond of aggregated all-atom molecular dynamics (MD) simulation data to identify the impact of N-glycans of four human SLC6 transporters: the serotonin transporter, dopamine transporter, glycine transporter, and neutral amino acid transporter B0AT1. We designed our computational study by first simulating all possible combination of a glycan attached to each glycosylation sites followed by investigating the effect of larger, oligo-N-linked glycans to each transporter. Our simulations reveal that glycosylation does not significantly affect transporter structure, but alters the dynamics of the glycosylated extracellular loop. The structural consequences of glycosylation on the loop dynamics are further emphasized in the presence of larger glycan molecules. However, no apparent trend in ligand stability or movement of gating helices was observed. In all, the simulations suggest that glycosylation does not consistently affect transporter structure and dynamics among the collective SLC6 family and should be characterized at a per-transporter level to further elucidate the underlining mechanisms of in vivo regulation.

PIGT promotes cell growth, glycolysis, and metastasis in bladder cancer by modulating GLUT1 glycosylation and membrane trafficking

“…Increasing evidences have shown that post-translational modifications such as glycosylation is implicated in transporter stability and membrane trafficking [29][30][31]. Therefore, we investigated whether PIGT influences the glycosylation of GLUT1.…”

Molecular Mechanisms of Na+-driven Bile Acid Transport in Human NTCP

“…Although cholesterol is physiologically present in the human membrane environment, it has been shown to bias the conformations of membrane peoteins 82,83 . As such, the cholesterol molecules were excluded to prevent unintended inhibition of transporter dynamics 84 . The CHARMM36m force field was used to describe the proteins 85 , and the parameters for substrate TCA were generated using the CHARMM general force field (CGenFF) 86 .…”

Thirty years of molecular dynamics simulations on posttranslational modifications of proteins

“…This point was emphasized by the Shukla group in their 2022 study on the effects of N-linked glycosylation on SLC6 transporters. 226 From over 1 ms of independent simulations using combinatoric glycosylation patterns across four different SLC6 transporters, Chan and Shukla concluded that the impacts of glycosylation should be characterized at a per-protein level regardless of shared function within a family. 226 And amazingly, across all studies implementing the ''single'' or ''few'' trajectories approach, decent extents of conformational change, and the conversion between different states, could be observed in very short amounts of simulation time.…”