The cold denaturation of IscU highlights structure\u2013function dualism in marginally stable proteins

Robert Yan,Paolo Delos Rios,Annalisa Pastore,Piero Andrea Temussi

doi:10.1038/s42004-018-0015-1

Abstract

Proteins undergo both cold and heat denaturation, but often cold denaturation cannot be detected because it occurs at temperatures below water freezing. Proteins undergoing detectable cold as well as heat denaturation yield a reliable curve of protein stability. Here we use bacterial IscU, an essential and ancient protein involved in iron cluster biogenesis, to show an important example of unbiased cold denaturation, based on electrostatic frustration caused by a dualism between iron–sulfur cluster binding and the presence of a functionally essential electrostatic gate. We explore the structural determinants and the universals that determine cold denaturation with the aid of a coarse grain model. Our results set a firm point in our understanding of cold denaturation and give us general rules to induce and predict protein cold denaturation. The conflict between ligand binding and stability hints at the importance of the structure–function dualism in protein evolution.

Highlights

Proteins undergo both cold and heat denaturation, but often cold denaturation cannot be detected because it occurs at temperatures below water freezing
We serendipitously discovered a small protein, yeast frataxin (Yfh1), which undergoes unbiased cold denaturation at temperatures above the water freezing point[4] and used it as a system to test the influence on protein stability of a variety of external factors[2,5,6,7]
We address the question of whether it is possible to understand the structural determinants of cold denaturation by showing that the behavior observed in Yfh[1] is not a singularity: we investigate the possible molecular mechanism of the cold denaturation of IscU

Summary

Introduction

Proteins undergo both cold and heat denaturation, but often cold denaturation cannot be detected because it occurs at temperatures below water freezing. We serendipitously discovered a small protein, yeast frataxin (Yfh1), which undergoes unbiased cold denaturation at temperatures above the water freezing point[4] and used it as a system to test the influence on protein stability of a variety of external factors[2,5,6,7]. Is it possible to identify other similar cases? We find that the relationship between the function of IscU, that concentrates negative charges within a small surface area, and its marginal stability is a further indication of the widespread dualism between structure and function in proteins

Methods

Results

Conclusion