Biology subjects

Kamel, M.

Publications and source records attributed to Kamel, M..

3 recordsLinked to original sources

bioRxiv2021

A single-cell atlas of de novo β-cell regeneration reveals the contribution of hybrid β/δ cells to diabetes recovery in zebrafish

Regeneration-competent species possess the ability to reverse the progression of severe diseases by restoring the function of the damaged tissue. However, the cellular dynamics underlying this capability remain unexplored. Here, we use single-cell transcriptomics to map de novo {beta}-cell regeneration during induction and recovery from diabetes in zebrafish. We show that the zebrafish has evolved two distinct types of somatostatin-producing {delta}-cells, which we term {delta}1- and {delta}2-cells. Moreover, we characterize a small population of glucose-responsive islet cells, which share the hormones and fate-determinants of both {beta}- and {delta}1-cells. The transcriptomic analysis of {beta}-cell regeneration reveals that {beta}/{delta} hybrid cells constitute a prominent source of insulin-expression during diabetes recovery. Using in vivo calcium imaging and cell tracking, we further show that the hybrid cells form de novo and acquire glucose-responsiveness in the course of regeneration. The overexpression of dkk3, a gene enriched in hybrid cells, increases their formation in the absence of {beta}-cell injury. Finally, interspecies comparison shows that plastic {delta}1-cells are partially related to PP-cells in the human pancreas. Our work provides an atlas of {beta}-cell regeneration and indicates that the rapid formation of glucose-responsive hybrid cells contributes to the resolution of diabetes in zebrafish

developmental biology↗

bioRxiv2021

Novel intracellular phospholipase B from Pseudomonas aeruginosa with activity towards endogenous phospholipids affects biofilm assembly

Pseudomonas aeruginosa is a severe threat to immunocompromised patients due to its numerous virulence factors and multiresistance against antibiotics. This bacterium produces and secretes various toxins with hydrolytic activities including phospholipases A, C and D. However, the function of intracellular phospholipases for bacterial virulence has still not been established. Here we demonstrate that the hypothetical gene pa2927 of P. aeruginosa encodes a novel phospholipase B named PaPlaB. PaPlaB isolated from detergent-solubilized membranes of E. coli rapidly degraded various GPLs including endogenous GPLs isolated from P. aeruginosa cells. Cellular localization studies suggest that PaPlaB is peripherally bound to the inner and outer membrane of E. coli, yet the active form was predominantly associated with the cytoplasmic membrane. In vitro activity of purified and detergent-stabilized PaPlaB increases at lower protein concentrations. The size distribution profile of PaPlaB oligomers revealed that decreasing protein concentration triggers oligomer dissociation. These results indicate that homooligomerisation regulates PaPlaB activity by a yet unknown mechanism, which might be required for preventing bacteria from self-disrupting the membrane. We demonstrated that PaPlaB is an important determinant of the biofilm lifestyle of P. aeruginosa, as shown by biofilm quantification assay and confocal laser scanning microscopic analysis of biofilm architecture. This novel intracellular phospholipase B with a putative virulence role contributes to our understanding of membrane GPL degrading enzymes and may provide a target for new therapeutics against P. aeruginosa biofilms.

biochemistry↗

bioRxiv2021

Unsaturated fatty acids augment protein transport via the SecA:SecYEG translocon

The translocon SecYEG forms the primary protein-conducting channel in the cytoplasmic membrane of bacteria, and the associated ATPase SecA provides the energy for the transport of secretory and cell envelope protein precursors. The translocation requires negative charge at the lipid membrane surface, but its dependence on the properties of the membrane hydrophobic core is not known. Here, we demonstrate that SecA:SecYEG-mediated protein transport is immensely stimulated by unsaturated fatty acids (UFAs). Furthermore, UFA-rich tetraoleoyl-cardiolipin, but not bis(palmitoyloleoyl)-cardiolipin, facilitate the translocation via the monomeric translocon. Biophysical analysis and molecular dynamics simulations show that UFAs determine the loosely packed membrane interface, where the N-terminal amphipathic helix of SecA docks. While UFAs do not affect the translocon folding, they promote SecA binding to the membrane, and the effect is enhanced manifold at elevated ionic strength. Tight SecA:lipid interactions convert into the augmented translocation. As bacterial cells actively change their membrane composition in response to their habitat, the modulation of SecA:SecYEG activity via the fatty acids may be crucial for protein secretion over a broad range of environmental conditions.

biophysics↗