Biology subjects

Sandhu, H.

Publications and source records attributed to Sandhu, H..

4 recordsLinked to original sources

bioRxiv2026

Binary partitioning of human brain organization due to divergent human cytoskeletal evolution

CHRFAM7A is a biallelic uniquely human fusion gene present in 99.3% of humans. The direct and inverted alleles likely emerged independently in Africa and East Asia. We uncovered that the inverted allele regulates ULK4 expression through genetic epistasis. The increase in long to short ULK4 isoform ratio enhances -tubulin acetylation leading to microtubule (MT) cytoskeleton phenotypes (cell body: microtubule rich projections; neurite: de-bundling; growth cone: fanning with MT invasion). The MT cytoskeleton gain of function enhances neuronal arborization and functional connectivity in the human brain. Considering that the previously reported direct allele leads to actin cytoskeleton gain of function, we propose that CHRFAM7A alleles represent binary human genetic background through divergent evolution of the cytoskeleton. In the human brain the two alleles represent distinct brain organization: the direct allele enhances microstructure as measured by diffusion tensor imaging while the inverted allele increases functional connectivity with increased small world propensity. The two types of brain organization likely represent different susceptibility to neuropsychiatric disease and may underlie the allelic disease associations. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=195 HEIGHT=200 SRC="FIGDIR/small/725959v1_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@a84e75org.highwire.dtl.DTLVardef@1b712d9org.highwire.dtl.DTLVardef@367c01org.highwire.dtl.DTLVardef@1074dc4_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Cotranslational folding of a periplasmic protein domain in Escherichia coli

In Gram-negative bacteria, periplasmic domains in inner membrane proteins are cotranslationally translocated across the inner membrane through the SecYEG translocon. To what degree such domains also start to fold cotranslationally is generally difficult to determine using currently available methods. Here, we apply Force Profile Analysis (FPA) - a method where a translational arrest peptide is used to detect folding-induced forces acting on the nascent polypeptide - to follow the cotranslational translocation and folding of the large periplasmic domain of the E. coli inner membrane protease LepB in vivo. Membrane insertion of LepBs two N-terminal transmembrane helices is initiated when their respective N-terminal ends reach 45-50 residues away from the peptidyl transferase center (PTC) in the ribosome. The main folding transition in the periplasmic domain involves all but the ~15 most C-terminal residues of the protein and happens when the C-terminal end of the folded part is ~70 residues away from the PTC; a smaller putative folding intermediate is also detected. This implies that wildtype LepB folds post-translationally in vivo, and shows that FPA can be used to study both co- and post-translational protein folding in the periplasm.

molecular biology↗

bioRxiv2019

Differential Effects of Prostaglandin E2 Production and Signaling through the Prostaglandin EP3 Receptor on Human Beta-cell Compensation

ObjectiveSignaling through Prostaglandin E3 Receptor (EP3), a G protein-coupled receptor for E series prostaglandins such as prostaglandin E2 (PGE2), has been linked to the beta-cell dysfunction and loss of beta-cell mass in type 2 diabetes (T2D). In the beta-cell, EP3 is specifically coupled to the unique cAMP-inhibitory G protein, Gz. Divergent effects of EP3 agonists and antagonists or Gz loss on beta-cell function, replication, and survival depending on whether islets are isolated from mice or humans in the lean and healthy, type 1 diabetic, or T2D state suggest a divergence in biological effects downstream of EP3/Gz dependent on the physiological milieu in which the islets reside.\n\nMethodsWe determined the expression of a number of genes in the EP3/Gz signaling pathway; PGE2 production pathway; and the beta-cell metabolic, proliferative, and survival responses to insulin resistance and its corresponding metabolic and inflammatory derangements in a panel of 80 islet preparations from non-diabetic human organ donors spanning a BMI range of approximately 20-45. In a subset of islet preparations, we also performed glucose-stimulated insulin secretion assays with and without the addition of an EP3 agonist, L798,106, and a glucagon-like peptide 1 receptor agonist, exendin-4, allowing us to compare the gene expression profile of each islet preparation with its (1) total islet insulin content (2), functional responses to glucose and incretin hormones, and (3) intrinsic influence of endogenous EP3 signaling in regulating these functional responses. We also transduced two independent islet preparations from three human organ donors with adenoviruses encoding human Gz or a GFP control in order to determine the impact of Gz hyperactivity (a mimic of the T2D state) on human islet insulin content and functional response to glucose.\n\nResultsIn contrast to results from islets isolated from T2D mice and human organ donors, where PGE2-mediated EP3 signaling actively contributes to beta-cell dysfunction, PGE2 production and EP3 expression appeared positively associated with various measurements of functional beta-cell compensation. While Gz mRNA expression was negatively associated with islet insulin content, that of each of the Gz-sensitive adenylate cyclase (AC) isoforms were positively associated with BMI and cyclin A1 mRNA expression, suggesting increased expression of AC1, AC5, and AC6 is a compensatory mechanism to augment beta-cell mass. Human islets over-expressing Gz via adenoviral transduction had reduced islet insulin content and secretion of insulin in response to stimulatory glucose as a percent of content, consistent with the effects of hyperactivation of Gz by PGE2/EP3 signaling observed in islets exposed to the T2D physiological milieu.\n\nConclusionsOur work sheds light on critical mechanisms in the human beta-cell compensatory response, before the progression to frank T2D.

molecular biology↗

bioRxiv2018

The Shape of the Ribosome Exit Tunnel Affects Cotranslational Protein Folding

The E.coli ribosome exit tunnel can accommodate small folded proteins, while larger ones fold outside. It remains unclear, however, to what extent the geometry of the tunnel influences protein folding. Here, using E. coli ribosomes with deletions in loops in proteins uL23 and uL24 that protrude into the tunnel, we investigate how tunnel geometry determines where proteins of different sizes fold. We find that a 29-residue zinc-finger domain normally folding close to the uL23 loop folds deeper in the tunnel in uL23 {Delta}loop ribosomes, while two ~100-residue protein normally folding close to the uL24 loop near the tunnel exit port fold at deeper locations in uL24 {Delta}loop ribosomes, in good agreement with results obtained by coarse-grained molecular dynamics simulations. This supports the idea that cotranslational folding commences once a protein domain reaches a location in the exit tunnel where there is sufficient space to house the folded structure.

biochemistry↗