NMR structure of Hsp12, a protein induced by and required for dietary restriction-induced lifespan extension in yeast.

Andrew P Herbert,Stephen R Pennington,Michèle Riesen,Lu-Yun Lian,Marie M Phelan,Alan Morgan,Leanne Bloxam,James R Johnson,Brian M Wareing,Effie Kosmidou,Matt Kaeberlein

doi:10.1371/journal.pone.0041975

Abstract

Dietary restriction (DR) extends lifespan in yeast, worms, flies and mammals, suggesting that it may act via conserved processes. However, the downstream mechanisms by which DR increases lifespan remain unclear. We used a gel based proteomic strategy to identify proteins whose expression was induced by DR in yeast and thus may correlate with longevity. One protein up-regulated by DR was Hsp12, a small heat shock protein induced by various manipulations known to retard ageing. Lifespan extension by growth on 0.5% glucose (DR) was abolished in an hsp12Δ strain, indicating that Hsp12 is essential for the longevity effect of DR. In contrast, deletion of HSP12 had no effect on growth under DR conditions or a variety of environmental stresses, indicating that the effect of Hsp12 on lifespan is not due to increased general stress resistance. Unlike other small heat shock proteins, recombinant Hsp12 displayed negligible in vitro molecular chaperone activity, suggesting that its cellular function does not involve preventing protein aggregation. NMR analysis indicated that Hsp12 is monomeric and intrinsically unfolded in solution, but switches to a 4-helical conformation upon binding to membrane-mimetic SDS micelles. The structure of micelle-bound Hsp12 reported here is consistent with its recently proposed function as a membrane-stabilising ‘lipid chaperone’. Taken together, our data suggest that DR-induced Hsp12 expression contributes to lifespan extension, possibly via membrane alterations.

Highlights

It is commonly accepted that similar fundamental cellular processes modulate ageing in most eukaryotes [1]
To identify proteins that are induced by dietary restriction (DR), we analysed extracts from BY4741 yeast cells grown under standard (2% glucose) or DR (0.5% glucose) conditions by 2-D gel electrophoresis
To help pinpoint DR-induced proteins that play a causal role in mediating lifespan extension, as opposed to those whose expression patterns are merely coincidental, we analysed proteins that were induced by high osmolarity (Fig. S1)

Summary

Introduction

It is commonly accepted that similar fundamental cellular processes modulate ageing in most eukaryotes [1] Evidence to support this idea comes from studies of dietary restriction (DR), i.e. underfeeding without malnutrition [2]. An alternative theory is that DR extends lifespan in a Sir2-independent manner by inhibition of the Tor and Sch kinase signalling pathways [12,13]. In this latter model, the downstream molecular mechanisms effecting longevity are not entirely clear, but may include reduced ribosomal protein biogenesis [13,14] as well as reduced rDNA recombination [15]

Methods

Results

Conclusion