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Structural probing of Hsp26 activation and client binding by quantitative cross-linking mass spectrometry

ABSTRACT: Small heat-shock proteins (sHSP) are important members of the cellular stress response in all species. Their best described function is the binding of early unfolding states and the resulting prevention of protein aggregation. All sHSPs exist as oligomers but vary in size and subunit organization. Some sHSPs exist as a polydisperse composition of oligomers which undergoes changes in subunit composition, folding status and relative distribution upon heat activation. To date only an incomplete picture of the mechanism of sHSP activation exists and in particularly the molecular basis of how sHSPs bind client proteins and mediate client specificity is not fully understood. In this study we have applied cross-linking mass spectrometry (XL-MS) to obtain detailed structural information on sHSP activation and client binding for yeast Hsp26. Our cross-linking data reveals the middle domain of Hsp26 as client-independent interface in multiple Hsp26::client complexes and indicates that client-specificity is likely mediated via additional binding sites with its αCD and CTE. Our quantitative XL-MS data underpins the middle domain as the main driver of heat-induced activation and client binding but shows that global rearrangements spanning all domains of Hsp26 are taking place simultaneously. We also investigated a Hsp26::client complex in the presence of Ssa1 (Hsp70) and Ydj1(Hsp40) at the initial stage of refolding and see that the interaction between refolding chaperones is altered by the presence of a client protein, pointing to a mechanism where interaction of Ydj1 with the HSP::client complex initiates assembly of the active refolding machinery.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Saccharomyces Cerevisiae (baker's Yeast)

SUBMITTER: Florian Stengel

LAB HEAD: Florian Stengel

PROVIDER: PXD026244 | Pride | 2021-08-13

REPOSITORIES: Pride

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			Action	DRS
	EXP_NAME_bagcontainer.details.stats.xls	Xls
	EXP_def.def	Other
	EXP_def_T.def	Other
	EXP_def_T_Hsponly.def	Other
	F1601_fuerschj_078_161109151508.raw	Raw

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Project description:Biological nitrogen fixation (BNF) is a primary input of nitrogen to natural and agricultural systems globally. BNF is a temperature-dependant enzymatic process and can be conducted by microbes (including Rhizobia) hosted symbiotically in root nodules of some plants. Heat shock proteins (Hsps) have been implicated in the process of acquiring thermotolerance or acclimating to elevated temperature, as they play a vital role in maintaining cell integrity and homeostasis during heat stress. Although the BNF response to temperature may crucially impact future ecosystem productivity in the face of global climate change, little is known about Hsp expression in nodules of N-fixing non-agricultural species, such as tropical N-fixing trees in the Fabaceae family. This project aimed to characterize small (15-20kDa) Hsp (sHsp) expression in nodule tissue to examine the biochemical mechanisms of heat response in these tissues. To first identify Hsps in nodule tissues, Vachellia farnesiana and Acacia confusa nodules were excised, heat shock was induced, and protein content was isolated via chemical treatment before separation of protein species and analysis with SDS-PAGE. Two polyacrylamide gels yielded bands in the 15-20 kDa region that displayed differential Coomassie staining, which were sent for further characterization by HPLC-MS analysis for protein sequencing. Ten rhizobial sHsps were detected in these samples in addition to seven Acacia sHsps when compared independently to reference rhizobial and plant proteome databases. In an attempt quantify relative expression of Hsps in nodule and root tissue, we performed western blot experiments using Anti-Hsp20 antibodies raised against human and mouse Hsp proteins, with anti-beta actin loading control. While nonuniform beta-actin expression across tissue types (A. confusa nodules versus root control) prevented quantitative analysis, the experiments validated that Hsp20s are expressed in Acacia nodules as well as in root tissue. These experiments could provide a foundation for future studies that aim to determine variation in responses to key stressors predicted to increase with global climate change and help determine the implications of warming across the tropics and beyond.

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Structural probing of Hsp26 activation and client binding by quantitative cross-linking mass spectrometry

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