# Mechanistic insights into mutation in the proton-coupled folate transporter (SLC46A1) causing hereditary folate malabsorption

## TL;DR

This study explores how mutations in the proton-coupled folate transporter (PCFT) lead to a rare disorder called hereditary folate malabsorption by examining structural changes in the protein.

## Contribution

The study provides novel mechanistic insights into how PCFT mutations cause structural instability, impairing folate transport and contributing to disease.

## Key findings

- Mutations in PCFT lead to structural instability, including enlarged pores and loss of secondary structures.
- Compensatory mutations can reverse these structural defects and restore PCFT function.
- The findings correlate structural changes with kinetic and biochemical properties of mutant PCFT proteins.

## Abstract

Hereditary folate malabsorption (HFM) is a rare, autosomal recessive disorder characterized by impaired intestinal absorption and impaired transport of folates across the choroid plexus into cerebral spinal fluid due to inactivating mutations in the human proton-coupled folate transporter (hPCFT) gene, which encodes the proton-coupled folate transporter (PCFT) SLC46A1. Understanding the structural impact of these mutations is crucial for elucidating the mechanistic basis for PCFT function and the pathophysiology of HFM. Recently, the cryo-electron microscopic structural characterization of the Gallus gallus PCFT was obtained, which shares significant sequence identity with hPCFT. We conducted molecular dynamics simulations of hPCFT based on this structure, to explore structural changes induced by functionally defective disease-causing and other mutant proteins and mutations that restore function. Simulations revealed that the mutually mechanistic basis for the loss of function is partial loss of structural integrity of hPCFT primarily manifested in an enlarged and distorted pore accompanied by loss of long-range contacts, less stable, fluctuating inner helices with reduced solvent accessibility, and a marked loss of ordered secondary structures. These changes are reversed by the introduction of compensatory mutations. These findings provide novel insights into the structural and functional consequences of PCFT mutations associated with HFM and provide correlations with kinetic and biochemical properties of the mutant proteins.