Wilson disease missense mutations in ATP7B affect metal-binding domain structural dynamics

Kumaravel Ponnandai Shanmugavel,Pernilla Wittung-Stafshede,Yaozong Li,Ranjeet Kumar

doi:10.1007/s10534-019-00219-y

Kumaravel Ponnandai Shanmugavel, Pernilla Wittung-Stafshede + Show 2 more

Open Access

https://doi.org/10.1007/s10534-019-00219-y

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Abstract

Wilson disease (WD) is caused by mutations in the gene for ATP7B, a copper transport protein that regulates copper levels in cells. A large number of missense mutations have been reported to cause WD but genotype–phenotype correlations are not yet established. Since genetic screening for WD may become reality in the future, it is important to know how individual mutations affect ATP7B function, with the ultimate goal to predict pathophysiology of the disease. To begin to assess mechanisms of dysfunction, we investigated four proposed WD-causing missense mutations in metal-binding domains 5 and 6 of ATP7B. Three of the four variants showed reduced ATP7B copper transport ability in a traditional yeast assay. To probe mutation-induced structural dynamic effects at the atomic level, molecular dynamics simulations (1.5 μs simulation time for each variant) were employed. Upon comparing individual metal-binding domains with and without mutations, we identified distinct differences in structural dynamics via root-mean square fluctuation and secondary structure content analyses. Most mutations introduced distant effects resulting in increased dynamics in the copper-binding loop. Taken together, mutation-induced long-range alterations in structural dynamics provide a rationale for reduced copper transport ability.

Highlights

Wilson disease (WD) is a rare autosomal recessivelyinherited disorder of copper (Cu) metabolism caused by mutations in the ATP7B gene which codes for a transmembrane Cu transporting ATPase (Park et al 1991; Mohr and Weiss 2019)
If an ATP7B mutation causes WD, the obvious speculation would be that the mutation hampers Cu transport by the mutated ATP7B protein
To investigate Cu transport ability by the four mutated ATP7B proteins, we turned to a yeast assay that has been used by many to assess ATP7B dysfunction (Forbes et al 1999; Ponnandai Shanmugavel et al 2017) and that was improved by us recently to include Cu delivery from human Atox1 (Ponnandai Shanmugavel et al 2017; Shanmugavel and WittungStafshede 2019)

Summary

Introduction

Wilson disease (WD) is a rare autosomal recessivelyinherited disorder of copper (Cu) metabolism caused by mutations in the ATP7B gene which codes for a transmembrane Cu transporting ATPase (Park et al 1991; Mohr and Weiss 2019). ATP7B has dual function, mediating excretion of Cu into the bile and Cu transport into the Golgi network for loading of Cu-dependent enzymes such as ceruloplasmin (Lo and Bandmann 2017). In patients, impaired Cu excretion leads to increased Cu accumulations, reaching toxic levels, primarily in the liver and eventually in other organs, in the brain. The wide spectrum of phenotypic variations in WD patients often makes it hard to make an accurate and early clinical diagnosis (Jang et al 2017; Dong et al 2016; Braiterman et al 2014)

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