CFTR trafficking mutations disrupt cotranslational protein folding by targeting biosynthetic intermediates

Hideki Shishido,Jae Seok Yoon,William R Skach,Zhongying Yang

doi:10.1038/s41467-020-18101-8

Abstract

Protein misfolding causes a wide spectrum of human disease, and therapies that target misfolding are transforming the clinical care of cystic fibrosis. Despite this success, however, very little is known about how disease-causing mutations affect the de novo folding landscape. Here we show that inherited, disease-causing mutations located within the first nucleotide-binding domain (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) have distinct effects on nascent polypeptides. Two of these mutations (A455E and L558S) delay compaction of the nascent NBD1 during a critical window of synthesis. The observed folding defect is highly dependent on nascent chain length as well as its attachment to the ribosome. Moreover, restoration of the NBD1 cotranslational folding defect by second site suppressor mutations also partially restores folding of full-length CFTR. These findings demonstrate that nascent folding intermediates can play an important role in disease pathogenesis and thus provide potential targets for pharmacological correction.

Highlights

Protein misfolding causes a wide spectrum of human disease, and therapies that target misfolding are transforming the clinical care of cystic fibrosis
We show that: (1) numerous NBD1folding mutations impact nascent polypeptide folding; (2) two mutations (A455E and L558S) in different regions of NBD1 delay cotranslational compaction of folding intermediates during a similar window of synthesis of the β-sheet core; (3) destabilizing effects of the ribosome augment the mutation-induced folding defect; and (4) correction of this transient defect via second site suppressor mutations partially restores trafficking of full-length CFTR in cells
Numerous missense mutations that disrupt CFTR folding have been identified within CFTR NBD1 subdomains, including the Nterminal subdomain (L441P and A455E), the N-terminal/α-helical subdomain interface (S492F), and the α-helical subdomain (I507del, F508del, V520F, L558S, A559T, R560K, and R560T)[2,45] (Fig. 1a)

Summary

Introduction

Protein misfolding causes a wide spectrum of human disease, and therapies that target misfolding are transforming the clinical care of cystic fibrosis. We show that inherited, disease-causing mutations located within the first nucleotide-binding domain (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) have distinct effects on nascent polypeptides. Genetic suppressor mutations that improve NBD1 folding efficiency or ICL4-NBD1 interactions can partially restore intracellular trafficking of F508del and certain other CFTR mutants[6,7,8], whereas correction of both defects restores folding to near wild-type levels. These results suggest that therapeutic agents, which improve cotranslational folding efficiency, could provide a pharmacological strategy for treating protein folding disorders.

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Conclusion