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

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.

SIMPLE binds specifically to PI4P through SIMPLE-like domain and participates in protein trafficking in the trans-Golgi network and/or recycling endosomes

“…In this study, we demonstrated that SIMPLE binds specifically to PI4P through the 115–141 region within the SLD, and that this binding was cysteine-independent. Recently, two groups independently revealed that SIMPLE is a monotopic zinc-binding protein, and that the function of cysteine residues outside the 114–139 hydrophobic helical region is to mediate zinc binding for stabilization of the protein structure [ 12 , 13 ]. On the other hand, the FYVE domain, which binds PI3P in a cysteine-dependent manner, requires two zinc ions for proper structure [ 23 ].…”

“…Ho et al . also reported that the 114–139 hydrophobic helical region interacts with phosphatidylethanolamine (PE) [ 12 ]. Using liposome sedimentation assays, we tested the ability of SIMPLE to bind PI4P.…”

“…recently reported that the 114–139 aa hydrophobic helical region within the SLD is responsible for membrane tethering [ 12 ]. Moreover, they and others have revealed that SIMPLE is a monotopic zinc-binding protein, and that the function of the cysteine residues outside the 114–139 aa hydrophobic helical region is to mediate zinc binding for stabilization of the protein structure [ 12 , 13 ]. However, given the evidence collected by Lee and colleagues that SIMPLE does not have E3 ubiquitin ligase activity [ 14 ], the exact role of the SLD remains to be elucidated.…”

“…On the other hand, another group reported that SIMPLE localizes in MVBs and is involved in the regulation of exosome production [ 16 ]. Aside from EEs and MVBs, SIMPLE has also been detected within the trans-Golgi network (TGN) [ 17 , 18 ], lysosomes [ 8 , 12 , 13 , 16 , 19 – 21 ], aggresomes [ 22 ], and the plasma membrane [ 18 ], though the function of SIMPLE within organelles other than EEs and MVBs remains unclear.…”

Novel EGR2 variant that associates with Charcot-Marie-Tooth disease when combined with lipopolysaccharide-induced TNF-α factor T49M polymorphism

“…8,16 Indeed, recent studies have shown that LITAF has a cysteine-rich region that coordinates zinc. 17,18 We explored whether LITAF could positively regulate the transcription of myelin genes. To this aim, HEK293 cells were cotransected with phPMP22enh-Luciferase and the plasmids encoding for the human LITAF sequence.…”