Abstract
The social amoeba Dictyostelium discoideum's proteome contains a vast array of simple sequence repeats, providing a unique model to investigate proteostasis. Upon conditions of cellular stress, D. discoideum undergoes a developmental process, transitioning from a unicellular amoeba to a multicellular fruiting body. Little is known about how proteostasis is maintained during D. discoideum's developmental process. Here, we have identified a novel α-crystallin domain-containing protein, heat shock protein 48 (HSP48), that is upregulated during D. discoideum development. HSP48 functions in part by forming a biomolecular condensate via its highly positively charged intrinsically disordered carboxy terminus. In addition to HSP48, the highly negatively charged primordial chaperone polyphosphate is also upregulated during D. discoideum development, and polyphosphate functions to stabilize HSP48. Upon germination, levels of both HSP48 and polyphosphate dramatically decrease, consistent with a role for HSP48 and polyphosphate during development. Together, our data demonstrate that HSP48 is strongly induced during Dictyostelium discoideum development. We also demonstrate that HSP48 forms a biomolecular condensate and that polyphosphate is necessary to stabilize the HSP48 biomolecular condensate.IMPORTANCE During cellular stress, many microbes undergo a transition to a dormant state. This includes the social amoeba Dictyostelium discoideum that transitions from a unicellular amoeba to a multicellular fruiting body upon starvation. In this work, we identify heat shock protein 48 (HSP48) as a chaperone that is induced during development. We also show that HSP48 forms a biomolecular condensate and is stabilized by polyphosphate. The findings here identify Dictyostelium discoideum as a novel microbe to investigate protein quality control pathways during the transition to dormancy.
Highlights
The social amoeba Dictyostelium discoideum’s proteome contains a vast array of simple sequence repeats, providing a unique model to investigate proteostasis
We previously discovered that D. discoideum contains a large number of ␣-crystallin domain-containing proteins, including four previously unidentified ␣-crystallin domain-containing proteins (Table 1) [16]. ␣-Crystallin domain-containing proteins have been implicated in the developmental process of some bacteria, leading us to hypothesize that they may participate in D. discoideum development [45, 46]
We identified one uncharacterized ␣-crystallin domain-containing protein, heat shock protein 48 (HSP48), whose transcript levels were induced greater than 1,000-fold in fruiting bodies msphere.asm.org 2
Summary
The social amoeba Dictyostelium discoideum’s proteome contains a vast array of simple sequence repeats, providing a unique model to investigate proteostasis. IMPORTANCE During cellular stress, many microbes undergo a transition to a dormant state This includes the social amoeba Dictyostelium discoideum that transitions from a unicellular amoeba to a multicellular fruiting body upon starvation. Cells elicit a number of responses, such as the induction of stress responsive genes, reduced translation, formation of phase-separated compartments, including stress granules, and the production of the chemical chaperone polyphosphate [1,2,3,4,5,6,7,8,9,10] Activation of these pathways provides defense mechanisms for cells to combat protein aggregation and promote cell survival. Under conditions of cellular stress, D. discoideum undergoes a developmental process transitioning from a single cellular amoeba to a multicellular fruiting body containing dormant spores [13, 14]. Though it is known that D. discoideum harbors a large number of ␣-crystallin domain-containing proteins, their function in D. discoideum remains largely unexplored [16]
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