Biology subjects

Lipke, P. N.

Publications and source records attributed to Lipke, P. N..

3 recordsLinked to original sources

bioRxiv2023

Strain and temperature dependent aggregation of Candida auris is attenuated by inhibition of surface amyloid proteins

Candida auris is a multi-drug resistant human fungal pathogen that has become a global threat to human health due to its drug resistant phenotype, persistence in the hospital environment and propensity for patient to patient spread. Isolates display variable aggregation that may affect the relative virulence of strains. Therefore, dissection of this phenotype has gained substantial interest in recent years. We studied eight clinical isolates from four different clades (I-IV); four of which had a strongly aggregating phenotype and four of which did not. Genome analysis identified polymorphisms associated with loss of cell surface proteins were enriched in weakly-aggregating strains. Additionally, we identified down-regulation of chitin synthase and chitinase genes involved in the synthesis and dissolution of the chitinous septum. Characterisation of the cells revealed no ultrastructural defects in cytokinesis or cell separation in aggregating isolates. Strongly and weakly aggregating strains did not differ in net surface charge or in cell surface hydrophobicity. The capacity for aggregation and for adhesion to polystyrene microspheres were also not correlated. However, aggregation and extracellular matrix formation were all increased at higher growth temperatures, and treatment with the amyloid protein inhibitor Thioflavin-T markedly attenuated aggregation. Genome analysis further indicated strain specific differences in the genome content of GPI-anchored proteins including those encoding genes with the potential to form amyloid proteins. Collectively our data suggests that aggregation is a complex strain and temperature dependent phenomenon that may be linked in part to the ability to form extracellular matrix and cell surface amyloids. HIGHLIGHTSThe amyloid inhibitor Thioflavin-T inhibited C. auris aggregation. Aggregating isolates do not exhibit any defects in cell separation. Genomic differences were identified between strongly aggregating and weakly-aggregating strains of C. auris. Aggregation did not correlate with surface charge or hydrophobicity of yeast cells.

microbiology↗

bioRxiv2021

Structure and conservation of amyloid spines from the Candida albicans Als5 adhesin including similarity to human LARKS

Candida Als family adhesins mediate adhesion to biological and abiotic substrates, as well as fungal cell aggregation and fungal-bacterial co-aggregation. The activity of at least two family members, Als5 and Als1, is dependent on amyloid-like protein aggregation that is initiated by shear force. Each Als adhesin has a [~]300-residue N-terminal Ig-like/invasin region. The following 108-residue, low complexity, threonine-rich (T) domain unfolds under shear to expose a critical amyloid-forming segment 322SNGIVIVATTRTV334 at the interface between the Ig-like/invasin domain 2 and the T domain of Candida albicans Als5. Amyloid prediction programs identified six potential amyloidogenic sequences in the Ig/invasin region and three others in the T domain of C. albicans Als5. Peptides derived from four of these sequences formed fibrils that bound thioflavin T, the amyloid indicator dye, and three of these revealed atomic-resolution structures of cross-{beta} spines. These are the first atomic-level structures for fungal adhesins. One of these segments, from the T domain, revealed kinked {beta}-sheets, similarly to LARKS (Low-complexity, Amyloid-like, Reversible, Kinked segments) found in human functional amyloids. Based on the cross-{beta} structures in Als proteins, we use evolutionary arguments to identify functional amyloidogenic sequences in other fungal adhesins. Thus, cross-{beta} structures are often involved in fungal pathogenesis and potentially in antifungal therapy. ImportanceFungal adhesins form cell-to-cell bonds in biofilms. Many of the cellular interactions are dependent on formation of amyloid-like cross-{beta} protein aggregates. Such structures are called functional amyloids because they perform physiological activities and they are dependent on the same types of protein interactions that form the more familiar amyloid deposits in neurodegenerative diseases. We have identified sequence segments that form cross-{beta} structures in the Als5 adhesin from the human pathogen Candida albicans. Such sequences are widespread among ALS family adhesins, including those from other human pathogens including Candida auris. Moreover, we revealed a structural similarity in a segment originating from Als5 threonine-rich low complexity region to human LARKS, pointing on a common structural motif coding for functional amyloids in different kingdoms of life.

microbiology↗

bioRxiv2020

Enzymatic analysis of yeast cell wall-resident GAPDH and its secretion

In yeast, many proteins are found both in the cytoplasmic and extracellular compartments, and consequently it can be difficult to distinguish non-conventional secretion from cellular leakage. We therefore monitored extracellular glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity of intact cells as a specific marker for non-conventional secretion. Extracellular GAPDH activity was proportional to the number of cells assayed, increased with incubation time, and was dependent on added substrates. Preincubation of intact cells with 100M dithiothreitol increased the reaction rate, consistent with increased access of the enzyme after reduction of cell wall disulfide crosslinks. Such treatment did not increase cell permeability to propidium iodide, in contrast to effects of higher concentrations of reducing agents. An amine-specific membrane-impermeant biotinylation reagent specifically inactivated extracellular GAPDH. The enzyme was secreted again after a 30-60-minute lag following the inactivation, and there was no concomitant increase in propidium iodide staining. There were about 4 x 104 active GAPDH molecules per cell at steady state, and secretion studies showed replenishment to that level one hour after inactivation. These results establish conditions for specific quantitative assays of cell wall proteins in the absence of cytoplasmic leakage and for subsequent quantification of secretion rates in intact cells. ImportanceEukaryotic cells secrete many proteins, including many proteins that do not follow the classical secretion pathway. Among these, the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is unexpectedly found in the walls of yeasts and other fungi, and in extracellular space in mammalian cell cultures. It is difficult to quantify extracellular GAPDH, because leakage of just a little of the very large amount of cytoplasmic enzyme can invalidate the determinations. We used enzymatic assays of intact cells, while also maintaining membrane integrity. The results lead to estimates of the amount of extracellular enzyme, and its rate of secretion to the wall in intact cells. Therefore, enzyme assays under controlled conditions can be used to investigate non-conventional secretion more generally.

cell biology↗