Mechanistic Insights into Protein Stability and Self-aggregation in GLUT1 Genetic Variants Causing GLUT1-Deficiency Syndrome

Abstract

Human sodium-independent glucose cotransporter 1 (hGLUT1) has been studied for its tetramerization and multimerization at the cell surface. Homozygous or compound heterozygous mutations in hGLUT1 elicit GLUT1-deficiency syndrome (GLUT1-DS), a metabolic disorder, which results in impaired glucose transport into the brain. The reduced cell surface expression or loss of function have been shown for some GLUT1 mutants. However, the mechanism by which deleterious mutations affect protein structure, conformational stability and GLUT1 oligomerization is not known and require investigation. In this review, we combined previous knowledge of GLUT1 mutations with hGLUT1 crystal structure to analyze native interactions and several natural single-point mutations. The modeling of native hGLUT1 structure confirmed the roles of native residues in forming a range of side-chain interactions. Interestingly, the modeled mutants pointed to the formation of a variety of non-native novel interactions, altering interaction networks and potentially eliciting protein misfolding. Selfaggregation of the last part of hGLUT1 was predicted using protein aggregation prediction tool. Furthermore, an increase in aggregation potential in the aggregation-prone regions was estimated for several mutants suggesting increased aggregation of misfolded protein. Protein stability change analysis predicted that GLUT1 mutant proteins are unstable. Combining GLUT1 oligomerization behavior with our modeling, aggregation prediction, and protein stability analyses, this work provides stateof-the-art view of GLUT1 genetic mutations that could destabilize native interactions, generate novel interactions, trigger protein misfolding, and enhance protein aggregation in a disease state.

Glut1 Deficiency Syndrome (Glut1DS): State of the art in 2020 and recommendations of the international Glut1DS study group

“…The impact of Glut1DS on these systems is complex and the subject of ongoing research. SLC2A1 variants could destabilize GLUT1 native interactions, generate novel interactions, trigger protein misfolding, and enhance protein aggregation 87 . Glut1DS could be influenced by noncoding RNA genes 88,89 as well as downstream defects in Glut1 translation, transcription, processing, activating, and trafficking 90,91 .…”

Endosomal GLUT3 is essential for alternative macrophage signaling, polarization, and function

“…As GLUT3 knockout did not significantly affect glucose uptake in BMDM, we next investigated whether the glucose transport function of GLUT3 was required for its role in stimulating STAT6 signaling. First, after identifying missense mutations that blocked glucose transport in the GLUT1 transporter without impacting protein stability, the orthologous missense mutations were generated in GLUT3 alleles (Deng et al , 2014; Raja and Kinne, 2020). After lentiviral transduction, WT and most mutant GLUT3 alleles were stably expressed and membrane localized in Rat2 fibroblasts (Supplementary Fig.…”

One Molecule for Mental Nourishment and More: Glucose Transporter Type 1—Biology and Deficiency Syndrome

“…Different SLC2A1 variants could destabilize Glut1 native interactions or generate novel interactions, initiate protein misfolding, enhance protein aggregation, or be influenced by non-coding RNA genes or by defects in translation, transcription, processing, and activating Glut1 protein [ 5 , 46 ]. In a small proportion of patients with Glut1DS, no SLC2A1 genetic defect can be identified, even after the additional use of MLPA (multiplex ligation-dependent probe amplification) analysis to detect copy number variations [ 12 ].…”