Biology subjects

Pei, S.

Publications and source records attributed to Pei, S..

3 recordsLinked to original sources

bioRxiv2020

Threshold concentration and random collision determine the growth of the phase-separated huntingtin inclusion from a stable core

The processes underlying formation and growth of unfolded protein inclusions are relevant to neurodegenerative diseases. In S. cerevisiae, inclusion bodies formed by mutant huntingtin have characteristics of phase-separated compartments: they are mobile, ovoid, and the contents are diffusible. We have used molecular genetics and quantitative confocal microscopy to probe the relationship between concentration and inclusion growth in vivo. Our analysis and modeling of the growth of mutant huntingtin inclusion bodies (mHtt IBs) suggests that there is a cytoplasmic threshold concentration that triggers the formation of an IB, regardless of proteasome capacity, and that reduction in cytoplasmic mHtt causes IBs to shrink. These findings confirm that the IB is a phase-separated compartment that continuously exchanges material with the cytoplasm. The growth rate of the IB is most consistent with a model in which material is incorporated through collision with the IB. A small remnant of the IB is relatively long-lasting, suggesting that the IB contains a core that is structurally distinct, and which may serve to nucleate it.

cell biology↗

bioRxiv2020

Irradiance modulates thermal niche in a previously undescribed low-light and cold-adapted nano-diatom

Diatoms have well-recognized roles in fixing and exporting carbon and supplying energy to marine ecosystems, but only recently have we begun to explore the diversity and importance of nano- and pico-diatoms. Here we describe a small (~5 m) diatom from the genus Chaetoceros Isolated from a wintertime temperate estuary (2{degrees} C, Narragansett Bay, RI), with a unique obligate specialization for low-light environments (< 120 mol photons m-2 sec-1). This diatom exhibits a striking interaction between irradiance and thermal responses whereby as temperatures increase, so does its susceptibility to light stress. Historical 18S rRNA amplicon data from our study site show this isolate was abundant throughout a six-year period, and its presence strongly correlates with winter and early spring months when light and temperature are low. Two ASVs matching this isolate had a circumpolar distribution in Tara Polar Ocean Circle samples, indicating its unusual light and temperature requirements are adaptations to life in a cold, dark environment. We expect this isolates low light, psychrophilic niche to shrink as future warming-induced stratification increases both light and temperature levels experienced by high latitude marine phytoplankton.

microbiology↗

bioRxiv2020

The unconventional cytoplasmic sensing mechanism for ethanol chemotaxis in Bacillus subtilis

Motile bacteria sense chemical gradients using chemoreceptors, which consist of distinct sensing and signaling domains. The general model is that the sensing domain binds the chemical and the signaling domain induces the tactic response. Here, we investigated the unconventional sensing mechanism for ethanol taxis in Bacillus subtilis. Ethanol and other short-chain alcohols are attractants for B. subtilis. Two chemoreceptors, McpB and HemAT, sense these alcohols. In the case of McpB, the signaling domain directly binds ethanol. We were further able to identify a single amino-acid residue Ala431 on the cytoplasmic signaling domain of McpB, that when mutated to a serine, reduces taxis to ethanol. Molecular dynamics simulations suggest ethanol binds McpB near residue Ala431 and mutation of this residue to serine increases coiled-coil packing within the signaling domain, thereby reducing the ability of ethanol to bind between the helices of the signaling domain. In the case of HemAT, the myoglobin-like sensing domain binds ethanol, likely between the helices encapsulating the heme group. Aside from being sensed by an unconventional mechanism, ethanol also differs from many other chemoattractants because it is not metabolized by B. subtilis and is toxic. We propose that B. subtilis uses ethanol and other short-chain alcohols to locate prey, namely alcohol-producing microorganisms. ImportanceEthanol is a chemoattractant for Bacillus subtilis even though it is not metabolized and inhibits growth. B. subtilis likely uses ethanol to find ethanol-fermenting microorganisms for prey. Two chemoreceptors sense ethanol: HemAT and McpB. HemATs myoglobin-like sensing domain directly binds ethanol, but the heme group is not involved. McpB is a transmembrane receptor consisting of an extracellular sensing domain and a cytoplasmic signaling domain. While most attractants bind the extracellular sensing domain, we found that ethanol directly binds between inter-monomer helices of the cytoplasmic signaling domain of McpB, using a mechanism akin to those identified in many mammalian ethanol-binding proteins. Our results indicate that the sensory repertoire of chemoreceptors extends beyond the sensing domain and can directly involve the signaling domain.

microbiology↗