Biology subjects

Allen, S. P.

Publications and source records attributed to Allen, S. P..

3 recordsLinked to original sources

bioRxiv2024

The structural and biophysical basis of substrate binding to the hydrophobic groove in Ubiquilin Sti1 domains

Ubiquilins are molecular chaperones that play multifaceted roles in proteostasis, with point mutations in UBQLN2 leading to altered phase separation properties and Amyotrophic Lateral Sclerosis (ALS). Our mechanistic understanding of this essential process has been hindered by a lack of structural information on the Sti1 domain, which is essential for Ubiquilin chaperone activity and phase separation. Here, we present the first crystal structure of a Ubiquilin family Sti1 domain bound to a transmembrane domain (TMD) and show that ALS mutations disrupt the Sti1-TMD interaction. We then demonstrate that Ubiquilins contain multiple conserved, internal sequences that bind to the Sti1 domain, including the PXX region which is a hotspot for ALS mutations. We propose that these placeholder sequences prevent solvent exposure of the Sti1 hydrophobic groove and contribute to the multivalency that drives Ubiquilin phase separation. Together, this work provides a new paradigm for understanding how Sti1 domains modulate Ubiquilin chaperone activity and phase separation and offer insights into the molecular basis of ALS pathogenesis.

biochemistry↗

bioRxiv2022

Evaluating the "cost of generating force" hypothesis across frequency in human running and hopping

The volume of active muscle and duration of extensor muscle force well-explain the associated metabolic energy expenditure across body mass and speed during level-ground running and hopping. However, if these parameters fundamentally drive metabolic energy expenditure, then they should pertain to multiple modes of locomotion and provide a simple framework for relating biomechanics to metabolic energy expenditure in bouncing gaits. Therefore, we evaluated the ability of the cost of generating force hypothesis to link biomechanics and metabolic energy expenditure during human running and hopping across step frequencies. We asked participants to run and hop at 0%, {+/-}8% and {+/-}15% of preferred step frequency. We calculated changes in active muscle volume, force duration, and metabolic energy expenditure. Overall, as step frequency increased, active muscle volume decreased due to postural changes via effective mechanical advantage (EMA) or duty factor. Accounting for changes in EMA and muscle volume better related to metabolic energy expenditure during running and hopping at different step frequencies than assuming a constant EMA and muscle volume. Thus, to ultimately develop muscle mechanics models that can explain metabolic energy expenditure across different modes of locomotion, we suggest more precise measures of muscle force production that include the effects of EMA.

physiology↗

bioRxiv2019

Macrophages utilize mitochondrial fission to enhance mROS production during responses to Streptococcus pneumoniae

Immunometabolism and regulation of mitochondrial reactive oxygen species (mROS) are critical determinants of the immune effector phenotype of differentiated macrophages. Mitochondrial function requires dynamic fission and fusion, but whether effector function is associated with altered dynamics during bacterial responses is unknown. We show that macrophage mitochondria undergo fission after 12 h of progressive ingestion of live Streptococcus pneumoniae (pneumococci). Fission is associated with progressive reduction in oxidative phosphorylation but increased mROS generation. Fission is enhanced by mROS production, PI3K{gamma} signaling and by cathepsin B, but not by inflammasome activation or IL-1{beta} generation. Reduced fission following PI3K{gamma} or cathepsin B inhibition is associated with reduced mROS generation and bacterial killing. Fission is associated with Parkin recruitment to mitochondria, but not mitophagy. Fission occurs upstream of apoptosis induction and independently of caspase activation. During macrophage innate responses to live bacteria mitochondria shift from oxidative phosphorylation and ATP generation to mROS production and microbicidal responses with a progressive shift towards mitochondrial fission.

immunology↗