Biology subjects

Alder, N. N.

Publications and source records attributed to Alder, N. N..

6 recordsLinked to original sources

bioRxiv2025

Mitochondria-Targeted Peptides and Bilayer Composition Modulate Membrane Electro-poration Under Elevated Electrochemical Stress

Several studies have used molecular dynamics (MD) simulations to examine the relationship between transmembrane potentials ({Delta}{Psi}m) and electroporation; however, research on how this relationship presents in complex membranes with heterogenous lipid compositions is limited. Here we use all-atom, double-bilayer MD simulations with explicitly-modeled{Delta}{Psi} m voltages to compare how membranes with homogenous vs. heterogenous lipid compositions respond to varying degrees of electrochemical stress. These two bilayer systems were also exposed to a mitochondria-targeted peptide named Elamipretide which has been shown experimentally to modulate membrane electrostatics. Additionally, we used Computational Electrophysiology (CompEL) MD simulations to analyze how lipid composition and peptide exposure influence rates of passive transmembrane ion flux during electroporation events. The addition of cardiolipin (CL) and Elamipretide increased membrane capacitance, decreasing the{Delta}{Psi} m for a given transmembrane charge imbalance ({delta}TM) and protecting bilayers against electroporation. These results expand our understanding of how more complex, biologically-relevant bilayers respond to electrochemical stress.

biophysics↗

bioRxiv2025

Lateral lipid packing governs bilayer solubilization by styrene-maleic acid copolymers: a case study with cardiolipin-containing membranes

Styrene-maleic acid (SMA) copolymers are powerful tools for the detergent-free solubilization of biological membranes. Yet the influence of specific lipids on SMA activity remains an open question. Here, we examined the effects of the mitochondriaspecific phospholipid cardiolipin on SMA-mediated membrane solubilization and their ability to form SMA-bound nanodiscs. To this end, we prepared a series of model membranes with cardiolipin and other test lipids with comparable surface charge and lateral packing characteristics. Using multiple independent experimental approaches, we found that cardiolipin inhibited SMA solubilization. Our results indicate that this effect was not attributable to headgroup charge effects, but rather to cardiolipininduced increase in lateral packing pressure at the interfacial region. Reduction of this lateral packing pressure using bilayer-active alcohols partially restored SMA solubilization. Our results highlight the importance of lipid geometry and packing in SMA nanodisc formation and could help guide the design of copolymers tailored to specific membranes.

molecular biology↗

bioRxiv2024

Perturbations in mitochondrial metabolism associated with defective cardiolipin biosynthesis: An in-organello real-time NMR study

Mitochondria are central to cellular metabolism; hence, their dysfunction contributes to a wide array of human diseases including cancer, cardiopathy, neurodegeneration, and heritable pathologies such as Barth syndrome. Cardiolipin, the signature phospholipid of the mitochondrion promotes proper cristae morphology, bioenergetic functions, and directly affects metabolic reactions carried out in mitochondrial membranes. To match tissue-specific metabolic demands, cardiolipin typically undergoes an acyl tail remodeling process with the final step carried out by the phospholipid-lysophospholipid transacylase tafazzin. Mutations in the tafazzin gene are the primary cause of Barth syndrome. Here, we investigated how defects in cardiolipin biosynthesis and remodeling impact metabolic flux through the tricarboxylic acid cycle and associated pathways in yeast. Nuclear magnetic resonance was used to monitor in real-time the metabolic fate of 13C3-pyruvate in isolated mitochondria from three isogenic yeast strains. We compared mitochondria from a wild-type strain to mitochondria from a {Delta}taz1 strain that lacks tafazzin and contains lower amounts of unremodeled cardiolipin, and mitochondria from a {Delta}crd1 strain that lacks cardiolipin synthase and cannot synthesize cardiolipin. We found that the 13C-label from the pyruvate substrate was distributed through about twelve metabolites. Several of the identified metabolites were specific to yeast pathways, including branched chain amino acids and fusel alcohol synthesis. Most metabolites showed similar kinetics amongst the different strains but mevalonate and -ketoglutarate, as well as the NAD+/NADH couple measured in separate nuclear magnetic resonance experiments, showed pronounced differences. Taken together, the results show that cardiolipin remodeling influences pyruvate metabolism, tricarboxylic acid cycle flux, and the levels of mitochondrial nucleotides.

biophysics↗

bioRxiv2021

Structure-Activity Relationships in the Design of Mitochondria-Targeted Peptide Therapeutics

Mitochondria play a central role in metabolic homeostasis; hence, dysfunction of this organelle underpins the etiology of many heritable and aging-related diseases. Mitochondria-targeted tetrapeptides with alternating cationic and aromatic residues, such as SS-31 (Elamipretide), show promise as therapeutic compounds. In this study, we conducted a quantitative structure-activity analysis of three alternative tetrapeptide analogs that differed with respect to aromatic side chain composition and sequence register, benchmarked against SS-31. Using NMR and molecular dynamics approaches, we obtained the first structural models for this class of compounds, showing that all analogs except for SS-31 form compact reverse turn conformations in the membrane-bound state. All peptide analogs bound cardiolipin-containing membranes, yet they had significant differences in equilibrium binding behavior and membrane interactions. Notably, the analogs had markedly different effects on membrane surface charge, supporting a mechanism in which modulation of membrane electrostatics is a key feature of their mechanism of action. All peptide analogs preserved survival and energy metabolism more effectively than SS-31 in cell stress models. Within our peptide set, the analog containing tryptophan side chains, SPN10, had the strongest impact on most membrane properties and showed greatest efficacy in cell culture studies. Taken together, these results show that side chain composition and register strongly influence the activity of these mitochondria-targeted peptides. Furthermore, this work helps provide a framework for the rational design of next-generation therapeutics with enhanced potency.

biochemistry↗

bioRxiv2020

Reduction of Elevated Proton Leak Rejuvenates Mitochondria in the Aged Cardiomyocyte

Aging-associated diseases, including cardiac dysfunction, are increasingly common in the population. However, the mechanisms of physiologic aging in general, and cardiac aging in particular, remain poorly understood. Age-related heart impairment, especially diastolic dysfunction in HFpEF is lacking a clinically effective treatment. Using the model of naturally aging mice and rats, we show direct evidence of increased proton leak in the aged heart mitochondria. Moreover, we identified ANT1 as mediating the increased proton permeability of old cardiomyocytes. Most importantly, the tetra-peptide drug SS-31 prevents age-related excess proton entry, decreases the mitochondrial flash activity and mitochondrial permeability transition pore opening, rejuvenates mitochondrial function by direct association with ANT1 and the mitochondrial ATP synthasome, and leads to substantial reversal of diastolic dysfunction. Our results uncover the excessive proton leak as a novel mechanism of age-related cardiac dysfunction and elucidate how SS-31 is able to reverse this clinically important complication of cardiac aging.

cell biology↗

bioRxiv2019

Molecular Mechanism of Action of Mitochondrial Therapeutic SS-31 (Elamipretide): Membrane Interactions and Effects on Surface Electrostatics

Mitochondrial dysfunction includes heritable diseases, acquired pathologies, and age-related declines in health. Szeto-Schiller (SS) peptides comprise a class of amphipathic tetrapeptides that have demonstrated efficacy in treating a wide array of mitochondrial disorders, and are believed to target mitochondrial membranes due to their enrichment in the anionic phospholipid cardiolipin (CL). However, little is known regarding how SS peptides interact with or alter the physical properties of lipid bilayers. In this study, we have analyzed the interactions of the lead compound SS-31 (Elamipretide) with model and mitochondrial membranes using biophysical and computational approaches. Our results show that this polybasic peptide partitions into the membrane interfacial region with affinity and binding density that are directly related to surface charge. SS-31 binding does not destabilize lamellar bilayers even at the highest binding concentrations; however, it does cause saturable alterations in lipid packing. Most notably, SS-31 modulates the surface electrostatic properties of model and mitochondrial membranes, which could play a significant role in the mitoprotective properties of this compound. As a proof of concept, we show that SS-31 alters ion distribution at the membrane interface with implications for maintaining mitochondrial membranes subject to divalent cation (calcium) stress. Taken together, these results support a mechanism of action in which SS peptides interact with lipid bilayers and alter the biophysical (primarily electrostatic) properties of mitochondrial membranes as their primary mechanism of action. Understanding this molecular mechanism is key to the development of future compound variants with enhanced efficacy.\n\nSignificanceSzeto-Schiller (SS) peptides are among the most promising therapeutic compounds for mitochondrial dysfunction. However, the molecular target(s) and the mechanism of action of SS peptides are poorly understood. In this study, we evaluate the interaction of the lead compound SS-31 (Elamipretide) with mitochondrial and synthetic model membranes using a host of biophysical techniques. Our results show that SS-31 membrane interaction is driven largely by the negative surface charge of mitochondrial membranes and that SS-31 alters lipid bilayer properties, most notably electrostatics at the membrane interface. This work supports a mechanism in which SS peptides act on a key physical property of mitochondrial membranes rather than with a specific protein complex, consistent with the exceptionally broad therapeutic efficacy of these compounds.

biophysics↗