# MLX phosphorylation stabilizes the ChREBP-MLX heterotetramer on tandem E-boxes to control carbohydrate and lipid metabolism

## TL;DR

This study shows that phosphorylation of MLX helps form a complex that controls carbohydrate and lipid metabolism in response to sugar levels.

## Contribution

The study identifies MLX phosphorylation as a key mechanism for ChREBP-MLX heterotetramer formation and metabolic regulation.

## Key findings

- MLX phosphorylation is necessary for ChREBP-MLX heterotetramer formation on the ChoRE.
- CK2 and GSK3 are identified as MLX kinases involved in this process.
- MLX phosphorylation is essential for maintaining sugar tolerance and lipid homeostasis in Drosophila.

## Abstract

Carbohydrate-responsive element binding protein (ChREBP) and Max-like protein X (MLX) form a heterodimeric transcription factor complex that couples intracellular sugar levels to carbohydrate and lipid metabolism. To promote the expression of target genes, two ChREBP-MLX heterodimers form a heterotetramer to bind a tandem element with two adjacent E-boxes, called carbohydrate-responsive element (ChoRE). How the ChREBP-MLX hetero-tetramerization is achieved and regulated remains poorly understood. Here, we show that MLX phosphorylation on an evolutionarily conserved motif is necessary for the heterotetramer formation on the ChoRE and the transcriptional activity of the ChREBP-MLX complex. We identified casein kinase 2 (CK2) and glycogen synthase kinase 3 (GSK3) as MLX kinases. High intracellular glucose-6-phosphate accumulation inhibits MLX phosphorylation and heterotetramer formation on the ChoRE, impairing ChREBP-MLX activity. Physiologically, MLX phosphorylation is necessary in Drosophila to maintain sugar tolerance and lipid homeostasis. Our findings suggest that MLX phosphorylation is a key mechanism for the ChREBP-MLX heterotetramer formation to regulate carbohydrate and lipid metabolism.

CK2-mediated MLX phosphorylation is an evolutionarily conserved signaling pathway that controls sugar and lipid metabolism.