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A widespread family of heat-resistant obscure (Hero) proteins protect against protein instability and aggregation

Fig 2

Hydrophilic and highly charged proteins are enriched in the boiled supernatants.

(A–B) LC-MS/MS analysis of lysates from Drosophila S2 (A) and human HEK293T (B) cells before and after boiling. Scatterplots indicate the PSM values (plus 1, to avoid zeros), which correlate with the protein amount, in the original crude lysates on the x-axes and those in the boiled supernatants on the y-axes. The identified proteins were divided into five groups according to the degrees of depletion or enrichment by boiling (Group I [most depleted] to Group V [most enriched]) and used for further analysis in C–J. (C–D) Violin plots of the median IUPred score of the proteins classified into the five groups in Drosophila (C) and humans (D). The proteins enriched by boiling are predicted to be much more disordered. (E–F) Boxplots of the proportion of hydrophilic or hydrophobic amino acids of the proteins classified into the five groups in Drosophila (E) and humans (F). The proteins enriched by boiling are more hydrophilic. Boxplot center and box edges indicate median and 25th or 75th percentiles, respectively, while whiskers indicate the median ± 1.5 × IQR or the most extreme observations within these limits, and outliers are plotted individually. (G–H) Boxplots of the DIOPT score of the proteins classified into the five groups in Drosophila (G) and humans (H). The proteins enriched by boiling are predicted to be evolutionally less conserved. Boxplot center and box edges indicate median and 25th or 75th percentiles, respectively, while whiskers indicate the median ± 1.5 × IQR or the most extreme observations within these limits, and outliers are plotted individually. (I–J) Violin plots of the pI values of the proteins classified into the five groups in Drosophila (I) and humans (J). The proteins enriched by boiling show the pI values concentrated in the acidic (approximately 5) or basic (approximately 10) range but avoiding the neutral (between 7 and 8) range. (K) Violin plots of the median IUPred score of the entire human proteome and that of the proteins selected by their high IUPred scores and expression levels. (L) Violin plots of the pI values of the entire human proteome and that of the highly disordered proteins selected by their high IUPred scores and expression levels. The selected proteins also show the pI values concentrated in the acidic or basic range but avoiding the neutral range. The PSM data pertaining to this figure can be found in S1 and S2 Tables files. DIOPT, DRSC Integrative Ortholog Prediction Tool; LC-MS/MS, liquid chromatography-mass spectrometry; pI, isoelectric point; PSM, peptide spectrum match.

Fig 2

doi: https://doi.org/10.1371/journal.pbio.3000632.g002