The topology, structure and PE interaction of LITAF underpin a Charcot-Marie-Tooth disease type 1C.

Lena Wartosch,Paul T Manna,Anita K Ho,Jane L Wagstaff,Stefan M V Freund,Seema Qamar,Elspeth F Garman,Rhys C Roberts

doi:10.1186/s12915-016-0332-8

Abstract

BackgroundMutations in Lipopolysaccharide-induced tumour necrosis factor-α factor (LITAF) cause the autosomal dominant inherited peripheral neuropathy, Charcot-Marie-Tooth disease type 1C (CMT1C). LITAF encodes a 17 kDa protein containing an N-terminal proline-rich region followed by an evolutionarily-conserved C-terminal ‘LITAF domain’, which contains all reported CMT1C-associated pathogenic mutations.ResultsHere, we report the first structural characterisation of LITAF using biochemical, cell biological, biophysical and NMR spectroscopic approaches. Our structural model demonstrates that LITAF is a monotopic zinc-binding membrane protein that embeds into intracellular membranes via a predicted hydrophobic, in-plane, helical anchor located within the LITAF domain. We show that specific residues within the LITAF domain interact with phosphoethanolamine (PE) head groups, and that the introduction of the V144M CMT1C-associated pathogenic mutation leads to protein aggregation in the presence of PE.ConclusionsIn addition to the structural characterisation of LITAF, these data lead us to propose that an aberrant LITAF-PE interaction on the surface of intracellular membranes contributes to the molecular pathogenesis that underlies this currently incurable disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0332-8) contains supplementary material, which is available to authorized users.

Highlights

Mutations in Lipopolysaccharide-induced tumour necrosis factor-α factor (LITAF) cause the autosomal dominant inherited peripheral neuropathy, Charcot-Marie-Tooth disease type 1C (CMT1C)
Of relevance to the current study, one particular duplication appears to have occurred in the common ancestor of the jawed vertebrates, leading to the eventual existence of two LITAF domain-containing genes in humans: the so-far uncharacterised CDIP1 gene, and the CMT1C-associated gene, LITAF (Additional file 2: Figure S2)
And despite the large lineage-specific expansions seen in the LITAF domain gene family as described, the canonical domain architecture – that is, a proline-rich domain at the N-terminus followed by a C-terminal LITAF domain – is conserved across eukaryotes, highlighting the likely requirement for both regions to be present for correct intracellular protein function (Additional file 3: Figure S3 and Additional file 4: Figure S4a)

Summary

Introduction

Mutations in Lipopolysaccharide-induced tumour necrosis factor-α factor (LITAF) cause the autosomal dominant inherited peripheral neuropathy, Charcot-Marie-Tooth disease type 1C (CMT1C). Peripheral nerves are composed of two main functional anatomical structures: axons and Schwann cells. Of the genes associated with demyelinating CMT, where Schwann cell dysfunction is thought to be the primary underlying pathology, the encoded proteins can be classified into three main groups: structural proteins of the myelin sheath, transcription. Ho et al BMC Biology (2016) 14:109 factors that activate the myelination programme and, interestingly, proteins that are known or predicted to function in intracellular membrane traffic [5]. While Schwann cellspecific expression of CMT-associated proteins explains particular subtypes of demyelinating CMT [6, 7], most CMT-associated genes with known or predicted roles in membrane traffic are widely expressed across diverse tissues and species. Understanding why mutations in these widely expressed genes lead to isolated demyelinating peripheral neuropathies requires further study at the molecular level

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