Expression and Characterization of Full-length Human Huntingtin, an Elongated HEAT Repeat Protein

James A Huntington,Louise C Serpell,David C Rubinsztein,Wei Li,Wendy J Carter

doi:10.1074/jbc.m511007200

James A Huntington, Louise C Serpell + Show 3 more

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https://doi.org/10.1074/jbc.m511007200

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Abstract

Huntington disease is an inherited neurodegenerative disorder that is caused by expanded CAG trinucleotide repeats, resulting in a polyglutamine stretch of >37 on the N terminus of the protein huntingtin (htt). htt is a large (347 kDa), ubiquitously expressed protein. The precise functions of htt are not clear, but its importance is underscored by the embryonic lethal phenotype in htt knock-out mice. Despite the fact that the htt gene was cloned 13 years ago, little is known about the properties of the full-length protein. Here we report the expression and preliminary characterization of recombinant full-length wild-type human htt. Our results support a model of htt composed entirely of HEAT repeats that stack to form an elongated superhelix.

Highlights

Huntington disease (HD)3 is an autosomal-dominant neurodegenerative disorder that is caused by expanded CAG trinucleotide repeats on the N terminus of the IT15 gene that encodes the protein huntingtin [1]
Preliminary characterization by circular dichroism, dynamic light scattering, electron microscopy, and limited proteolysis supports a model of htt predominantly composed of HEAT repeats that stack into a rod-like superhelical structure
Despite the fact that 13 years have passed since the discovery of the htt gene, this is the

Summary

Introduction

Huntington disease (HD) is an autosomal-dominant neurodegenerative disorder that is caused by expanded CAG trinucleotide repeats on the N terminus of the IT15 gene that encodes the protein huntingtin (htt) [1]. The toxicity of mutant htt may only be fully exposed after cleavage by proteases, including caspases, calpains, and a putative aspartic protease, to reveal a short, N-terminal polyQ-containing fragment of 100 –150 residues N-terminal cleavage products have been found in inclusions from HD patients (16 – 18), and N-terminal fragments with expanded polyQs readily form inclusions similar to those seen in HD patients It is still unclear which combination of proteolytic events is required for generation of the toxic fragments. Recent data suggest that wild-type htt may have a beneficial effect on the gain-of-function toxicity of the mutant protein [20, 21]. Preliminary characterization by circular dichroism, dynamic light scattering, electron microscopy, and limited proteolysis supports a model of htt predominantly composed of HEAT repeats that stack into a rod-like superhelical structure

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