Mechanisms of lifespan extension in yeast

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Identification and Characterization of a Neospora caninum Microneme-Associated Protein (NcMIC4) That Exhibits Unique Lactose-Binding Properties

Microneme proteins have been shown to play an important role in the early phase of host cell adhesion, by mediating the contact between the parasite and host cell surface receptors. In this study we have identified and characterized a lectin-like protein of Neospora caninum tachyzoites which was purified by α-lactose-agarose affinity chromatography. Upon separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, this lactose-binding protein migrated at 70 and 55 kDa under reducing and nonreducing conditions, respectively. Immunofluorescence and immunogold electron microscopy with affinity-purified antibodies showed that the protein was associated with the tachyzoite micronemes. Mass spectrometry analyses and expressed sequence tag database mining revealed that this protein is a member of the Neospora microneme protein family; the protein was named NcMIC4 (N. caninum microneme protein 4). Upon two-dimensional gel electrophoresis, NcMIC4 separated into seven distinct isoforms. Incubation of extracellular parasites at 37°C resulted in the secretion of NcMIC4 into the medium as a soluble protein, and the secreted protein exhibited a slightly reduced M(r) but retained its lactose-binding properties. Immunofluorescence was used to investigate the temporal and spatial distribution of NcMIC4 in tachyzoites entering their host cells and showed that reexpression of NcMIC4 took place 30 min after entry into the host cell. Incubation of secreted fractions and purified NcMIC4 with Vero cells demonstrated binding of NcMIC4 to Vero cells as well as binding to chondroitin sulfate A glycosaminoglycans

A Random Mutagenesis Approach to Isolate Dominant-Negative Yeast sec1 Mutants Reveals a Functional Role for Domain 3a in Yeast and Mammalian Sec1/Munc18 Proteins

SNAP receptor (SNARE) and Sec1/Munc18 (SM) proteins are required for all intracellular membrane fusion events. SNAREs are widely believed to drive the fusion process, but the function of SM proteins remains unclear. To shed light on this, we screened for dominant-negative mutants of yeast Sec1 by random mutagenesis of a GAL1-regulated SEC1 plasmid. Mutants were identified on the basis of galactose-inducible growth arrest and inhibition of invertase secretion. This effect of dominant-negative sec1 was suppressed by overexpression of the vesicle (v)-SNAREs, Snc1 and Snc2, but not the target (t)-SNAREs, Sec9 and Sso2. The mutations isolated in Sec1 clustered in a hotspot within domain 3a, with F361 mutated in four different mutants. To test if this region was generally involved in SM protein function, the F361-equivalent residue in mammalian Munc18-1 (Y337) was mutated. Overexpression of the Munc18-1 Y337L mutant in bovine chromaffin cells inhibited the release kinetics of individual exocytosis events. The Y337L mutation impaired binding of Munc18-1 to the neuronal SNARE complex, but did not affect its binary interaction with syntaxin1a. Taken together, these data suggest that domain 3a of SM proteins has a functionally important role in membrane fusion. Furthermore, this approach of screening for dominant-negative mutants in yeast may be useful for other conserved proteins, to identify functionally important domains in their mammalian homologs

Helical properties of micelle-bound Hsp12.

<p>(A) The four α-helices are represented as ribbons and colour coded from the N-terminus (blue) to the C-terminus (red) in a representative structure. (B,C) Analysis of charge distribution with hydrophobic residues labelled green and charged residues labelled red in both ribbon (B) and surface (C) representation, illustrating the amphipathic nature of Hsp12. Structures were generated using Chimera.</p

Backbone dynamics and chemical shift-based secondary structure of Hsp12.

<p><i>T</i>₁, <i>T</i>₂ and <i>T</i>₁/<i>T</i>₂ relaxation values are shown for Hsp12 in the presence (A,C,E) and absence (B,D,F) of 100 mM SDS at 318 K. <i>T</i>₁ and <i>T</i>₂ relaxation times for micelle-bound (A,C) Hsp12 show significant variation; contrasting with the similar relaxation values observed for free Hsp12 (B,D). Micelle-bound Hsp12 (E) shows grouped variations in the <i>T</i>₁/<i>T</i>₂ values ranging from approximately 1.5 to 14, indicating a wide range of mobility and a clear differentiation of secondary structure elements; whereas the free form (F) shows consistent values of around 2, indicating a completely unstructured protein. (G) The assigned chemical shifts at 318 K in 100 mM SDS expressed as deviation from random coil are shown aligned with the primary sequence and the positions of the α-helices.</p

Ensemble of structures calculated for micelle-bound Hsp12 overlaid on each of the four helices.

<p>Ensemble of twenty structures overlaid on helices I (A), II (B), III (C) and IV (D). No long-range interactions were detected and so the helices appear free to move independently with no overall fold being evident.</p

DR induces expression of a relatively small number of proteins.

<p>Wild type BY4741 yeast cells were grown in standard (2% glucose) and DR (0.5% glucose) conditions before lysis and separation of proteins by 2-D electrophoresis. Wide-range (pH 3–10) gels revealed no obvious reproducible differences in protein expression, as illustrated by representative gels shown in panel (A). Narrow pH range gels (pH 3–5.6 and 5.3–6.5) revealed changes in protein spots, which were identified by mass spectrometry. Selected identified proteins are indicated by arrows in panels (B) and (C).</p