Mitochondrial membrane lipidome defines yeast longevity

Our studies revealed that lithocholic acid (LCA), a bile acid, is a potent anti‐aging natural compound that in yeast cultured under longevity‐extending caloric restriction (CR) conditions acts in synergy with CR to enable a significant further increase in chronological lifespan. Here, we investigate a mechanism underlying this robust longevity‐extending effect of LCA under CR. We found that exogenously added LCA enters yeast cells, is sorted to mitochondria, resides mainly in the inner mitochondrial membrane, and also associates with the outer mitochondrial membrane. LCA elicits an age‐related remodeling of glycerophospholipid synthesis and movement within both mitochondrial membranes, thereby causing substantial changes in mitochondrial membrane lipidome and triggering major changes in mitochondrial size, number and morphology. In synergy, these changes in the membrane lipidome and morphology of mitochondria alter the age‐related chronology of mitochondrial respiration, membrane potential, ATP synthesis and reactive oxygen species homeostasis. The LCA‐driven alterations in the age‐related dynamics of these vital mitochondrial processes extend yeast longevity. In sum, our findings suggest a mechanism underlying the ability of LCA to delay chronological aging in yeast by accumulating in both mitochondrial membranes and altering their glycerophospholipid compositions. We concluded that mitochondrial membrane lipidome plays an essential role in defining yeast longevity

A Human-Curated Annotation of the Candida albicans Genome

Recent sequencing and assembly of the genome for the fungal pathogen Candida albicans used simple automated procedures for the identification of putative genes. We have reviewed the entire assembly, both by hand and with additional bioinformatic resources, to accurately map and describe 6,354 genes and to identify 246 genes whose original database entries contained sequencing errors (or possibly mutations) that affect their reading frame. Comparison with other fungal genomes permitted the identification of numerous fungus-specific genes that might be targeted for antifungal therapy. We also observed that, compared to other fungi, the protein-coding sequences in the C. albicans genome are especially rich in short sequence repeats. Finally, our improved annotation permitted a detailed analysis of several multigene families, and comparative genomic studies showed that C. albicans has a far greater catabolic range, encoding respiratory Complex 1, several novel oxidoreductases and ketone body degrading enzymes, malonyl-CoA and enoyl-CoA carriers, several novel amino acid degrading enzymes, a variety of secreted catabolic lipases and proteases, and numerous transporters to assimilate the resulting nutrients. The results of these efforts will ensure that the Candida research community has uniform and comprehensive genomic information for medical research as well as for future diagnostic and therapeutic applications

Functional Characterization of Myosin I Tail Regions in Candida albicans

The molecular motor myosin I is required for hyphal growth in the pathogenic yeast Candida albicans. Specific myosin I functions were investigated by a deletion analysis of five neck and tail regions. Hyphal formation requires both the TH1 region and the IQ motifs. The TH2 region is important for optimal hyphal growth. All of the regions, except for the SH3 and acidic (A) regions that were examined individually, were required for the localization of myosin I at the hyphal tip. Similarly, all of the domains were required for the association of myosin I with pelletable actin-bound complexes. Moreover, the hyphal tip localization of cortical actin patches, identified by both rhodamine-phalloidin staining and Arp3-green fluorescent protein signals, was dependent on myosin I. Double deletion of the A and SH3 domains depolarized the distribution of the cortical actin patches without affecting the ability of the mutant to form hyphae, suggesting that myosin I has distinct functions in these processes. Among the six myosin I tail domain mutants, the ability to form hyphae was strictly correlated with endocytosis. We propose that the uptake of cell wall remodeling enzymes and excess plasma membrane is critical for hyphal formation

Phosphorylation of the MAPKKK Regulator Ste50p in Saccharomyces cerevisiae: a Casein Kinase I Phosphorylation Site Is Required for Proper Mating Function

The Ste50 protein of Saccharomyces cerevisiae is a regulator of the Ste11p protein kinase. Ste11p is a member of the MAP3K (or MEKK) family, which is conserved from yeast to mammals. Ste50p is involved in all the signaling pathways that require Ste11p function, yet little is known about the regulation of Ste50p itself. Here, we show that Ste50p is phosphorylated on multiple serine/threonine residues in vivo. Threonine 42 (T42) is phosphorylated both in vivo and in vitro, and the protein kinase responsible has been identified as casein kinase I. Replacement of T42 with alanine (T42A) compromises Ste50p function. This mutation abolishes the ability of overexpressed Ste50p to suppress either the mating defect of a ste20 ste50 deletion mutant or the mating defect of a strain with a Ste11p deleted from its sterile-alpha motif domain. Replacement of T42 with a phosphorylation-mimetic aspartic acid residue (T42D) permits wild-type function in all assays of Ste50p function. These results suggest that phosphorylation of T42 of Ste50p is required for proper signaling in the mating response. However, this phosphorylation does not seem to have a detectable role in modulating the high-osmolarity glycerol synthesis pathway

Identification of Spurious Genes

<div><p>Assessing criteria that identify candidate spurious genes in <i>S. cerevisiae,</i> using a reference set of known spurious genes [<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0010001#pgen-0010001-b16" target="_blank">16</a>].</p> <p>(A) For every gene in <i>S. cerevisiae,</i> the average Pearson correlation coefficient with all other genes was calculated. Shown are histograms of the correlations associated with genes characterized as spurious in the reading frame conservation test ([<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0010001#pgen-0010001-b16" target="_blank">16</a>]; red) and all genes in the genome (black).</p> <p>(B) The distribution of gene lengths is shown for genes characterized as spurious (red) and for all genes of the genome (black).</p> <p>(C) Assessing the likelihood of being spurious as a function of gene length and correlation score. Shown is the proportion of spurious genes out of all genes whose length and correlation score fall into each of the intervals. The proportion is color-coded according to the color bar shown. <i>S. cerevisiae</i> genes with an ortholog in <i>C. albicans</i> were excluded from the analysis.</p></div

Visualization of Protein Sequence Similarities

<p>Sample from a Web page used by annotators of the <i>C. albicans</i> genome to visualize the significance of the best hit from whole-proteome BLASTP searches. Each putative ORF was compared to the NR database, the <i>Candida</i> ORF list itself (Ca19; showing results from the four top hits), and amino acid sequences from the proteomes of <i>S. cerevisiae</i> (Sac), <i>S. pombe</i> (S.p), <i>M. grisea</i> (Mag), <i>N. crassa</i> (Neu), <i>H. sapiens</i> (H.S), <i>M. musculus</i> (M.m), <i>D. melanogaster</i> (Dro), <i>C. elegans</i> (C.e), and <i>A. thaliana</i> (A.t). The BLASTP <i>e</i>-value from the top hit was converted to a color scale as indicated. Examples of <i>C. albicans</i> genes with interesting similarity patterns are indicated.</p