Dynamic remodeling of the interactomes of Nematostella vectensis Hsp70 isoforms under heat shock.

Heat shock protein 70s (Hsp70s) are a highly conserved class of molecular chaperones that fold a large proportion of the proteome. Nematostella vectensis (Nv) is an estuarine sea anemone that has emerged as a model species to characterize molecular responses to physiological stressors due to its exposure to diverse, extreme abiotic conditions. Previous transcriptional data has shown dramatic differences among expression profiles of three NvHsp70 isoforms (NvHsp70A, B and D) under stress but it is unknown if, and to what extent, the client proteins for these chaperones differ. In order to determine client specificity, NvHsp70A, B and D were expressed in Saccharomyces cerevisiae budding yeast lacking native Hsp70 and interacting proteins for each Hsp70 were determined with mass spectrometry in yeast ambient and heat shock conditions. Our analyses showed <50% of identified interacting proteins were common to all three anemone Hsp70s and 3–18% were unique to an individual Hsp70. Mapping of temperature induced interactions suggest that under stress a proportion of clients are transferred from NvHsp70A and NvHsp70D to NvHsp70B. Together, these data suggest a diverse set of interacting proteins for Hsp70 isoforms that likely determines the precise functions for Hsp70s in organismal acclimation and potentially adaptation. Although the Hsp70 family of molecular chaperones has been studied for >50 years, it is still not fully understood why organisms encode and express many highly-similar Hsp70 isoforms. The prevailing theory is that these isoforms have identical function, but are expressed under unique cellular conditions that include heat shock to cope with increased number of unfolded/misfolded proteins. The sea anemone Nematostella vectensis encodes three Hsp70 isoforms A, B and D that when expressed in yeast demonstrate unique functionalities. This study provides the interactome of NvHsp70s A, B and D and demonstrates that Hsp70 isoforms, while highly similar in sequence, have unique co-chaperone and client interactors. Summary of NvHsp70 isoform response to heat shock. NvHsp70A binds HSF maintaining fidelity of the HSF-Hsp70-unfolded protein system. Upon heat stress, HSF-NvHsp70A interaction decreases, promoting expression of NvHsp70A and NvHsp70B. In contrast, NvHsp70D is constitutively expressed, except under chronic temperature stress. Heat stress promotes inter-Hsp70 isoform exchange of clients, with many clients involved in fatty acid synthesis and protein folding transferring from NvHsp70A and D, to NvHsp70B. Unlabelled Image • The global interactomes of NvHsp70A, B and D when expressed in yeast • Plasticity of NvHsp70A, B and D interactomes upon heat shock • Identification of unique binding of NvHsp70A to Hsf1 • Inter-Hsp70 isoform client transfer upon heat shock [ABSTRACT FROM AUTHOR]