Biology subjects

Bettinger, J. Q.

Publications and source records attributed to Bettinger, J. Q..

5 recordsLinked to original sources

bioRxiv2024

Pervasive divergence in protein thermostability is mediated by both structural changes and cellular environments

Temperature is a universal environmental constraint and organisms have evolved diverse mechanisms of thermotolerance. A central feature of thermophiles relative to mesophiles is a universal shift in protein stability, implying that it is a major constituent of thermotolerance. However, organisms have also evolved extensive buffering systems, such as those that disaggregate and refold denatured proteins and enable survival of heat shock. Here, we show that both cellular and protein structural changes contribute to divergence in protein thermostability between two closely related Saccharomyces species that differ by 8{degrees}C in their thermotolerance. Using thermal proteomic profiling we find that 85% of S. cerevisiae proteins are more stable than their S. uvarum homologs and there is an average shift of 1.6{degrees}C in temperature induced protein aggregation. In an interspecific hybrid of the two species, S. cerevisiae proteins retain their thermostability, while the thermostability of their S. uvarum homologs is enhanced, indicating that cellular context contributes to protein stability differences. By purifying orthologous proteins we show that amino acid substitutions underlie melting temperature differences for two proteins, Guk1 and Aha1. Amino acid substitutions are also computationally predicted to contribute to stability differences for most of the proteome. Our results imply that coordinated changes in protein thermostability impose a significant constraint on the time scales over which thermotolerance can evolve.

evolutionary biology↗

bioRxiv2022

Accurate proteome-wide measurement of methionine oxidation in aging mouse brains

The oxidation of methionine side chains has emerged as an important posttranslational modification of proteins. A diverse array of low-throughput and targeted studies have suggested that the oxidation of methionine residues in select proteins can have diverse impacts on cell physiology, ranging from detrimental effects on protein structure and stability to functional roles in cell signaling. Despite its importance, the large-scale investigation of methionine oxidation in a complex matrix, such as the cellular proteome, has been historically hampered by technical limitations. Herein we report a methodology, Methionine Oxidation by Blocking (MobB), that allows for accurate and precise quantification of low levels of methionine oxidation typically observed in vivo. To demonstrate the utility of this methodology, we applied MobB to the brain tissues of young (6 m.o.) and old (20 m.o.) mice and identified over 280 novel sites for in vivo methionine oxidation. We further demonstrated that oxidation stoichiometries for specific methionine residues are highly consistent between individual animals and methionine sulfoxides are enriched in clusters of functionally related gene products including membrane and extracellular proteins. However, we did not detect significant changes in methionine oxidation in brains of old mice. Our results suggest that under normal in vivo conditions methionine oxidation is a biologically regulated process rather than a result of stochastic chemical damage.

biochemistry↗

bioRxiv2021

Protein folding stabilities are a major determinant of oxidation rates for buried methionine residues

The oxidation of protein-bound methionines to form methionine sulfoxides has a broad range of biological ramifications, making it important to delineate factors that influence methionine oxidation rates within a protein. This is especially important for biopharmaceuticals, where oxidation can lead to deactivation and degradation. Previously, neighboring residue effects and solvent accessibility (SA) have been shown to impact the susceptibility of methionine residues to oxidation. In this study, we provide proteome-wide evidence that oxidation rates of buried methionine residues are also strongly influenced by the thermodynamic folding stability of proteins. We surveyed the E. coli proteome using several proteomic methodologies and globally measured oxidation rates of methionines in the presence and absence of tertiary structure, as well as folding stabilities of methionine containing domains. The data indicate that buried methionines have a wide range of protection factors against oxidation which correlate strongly with folding stabilities. Concordantly, we show that in comparison to E. coli, the proteome of the thermophile T. thermophilus is significantly more stable and thus more resistant to methionine oxidation. These results indicate that oxidation rates of buried methionines from the native state of proteins can be used as a metric of folding stability. To demonstrate the utility of this correlation, we used native methionine oxidation rates to survey the folding stabilities of E. coli and T. thermophilus proteomes at various temperatures and suggest a model that relates the temperature dependence of the folding stabilities of these two species to their optimal growth temperatures.

biochemistry↗

bioRxiv2019

Quantitative analysis of in vivo methionine oxidation of the human proteome

The oxidation of methionine is an important posttranslational modification of proteins with numerous roles in physiology and pathology. However, the quantitative analysis of methionine oxidation on a proteome-wide scale has been hampered by technical limitations. Methionine is readily oxidized in vitro during sample preparation and analysis. In addition, there is a lack of enrichment protocols for peptides that contain an oxidized methionine residue; making the accurate quantification of methionine oxidation difficult to achieve on a global scale. Herein, we report a methodology to circumvent these issues by isotopically labeling unoxidized methionines with 18O labeled hydrogen peroxide and quantifying the relative ratios of 18O and 16O oxidized methionines. We validate our methodology using artificially oxidized proteomes made to mimic varying degrees of methionine oxidation. Using this method, we identify and quantify a number of novel sites of in vivo methionine oxidation in an unstressed human cell line.

biochemistry↗

bioRxiv2018

Global analysis of methionine oxidation provides a census of folding stabilities for the human proteome

The stability of proteins influences their tendency to aggregate, undergo degradation or become modified in cells. Despite their significance to understanding protein folding and function, quantitative analyses of thermodynamic stabilities have been mostly limited to soluble proteins in purified systems. We have used a highly multiplexed proteomics approach, based on analyses of methionine oxidation rates, to quantify stabilities of ~10,000 unique regions within ~3,000 proteins in human cell extracts. The data identify lysosomal and extracellular proteins as the most stable ontological subsets of the proteome. We show that the stability of proteins impacts their tendency to become oxidized and is globally altered by the osmolyte trimethylamine-N-oxide (TMAO). We also show that most proteins designated as intrinsically disordered retain their unfolded structure in the complex environment of the cell. Together, the data provide a census of the stability of the human proteome and validate a methodology for global quantitation of folding thermodynamics.

biochemistry↗