Biology subjects

Norris, N.

Publications and source records attributed to Norris, N..

4 recordsLinked to original sources

bioRxiv2024

Optimised proteomic analysis of insulin granules from MIN6 β-cells identifies Scamp3, a novel regulator of insulin secretion and content

Pancreatic {beta}-cells in the islets of Langerhans are key to maintaining glucose homeostasis, by secreting the peptide hormone insulin. Insulin is packaged within vesicles named insulin secretory granules (ISGs), that have recently been considered to have intrinsic structures and proteins that regulate insulin granule maturation, trafficking, and secretion. Previously, studies have identified a handful of novel ISG-associated proteins using different separation techniques. Here, this study combines an optimized ISG isolation technique and mass spectrometry-based proteomics, with an unbiased protein correlation profiling and targeted machine learning approach to uncover 211 ISG-associated proteins. Five of these proteins: Syntaxin-7, Synaptophysin, Synaptotagmin-13, Zinc transporter ZIP8 and SCAMP3 have not been previously ISG-associated. Through colocalization analysis of confocal imaging we validate the association of these proteins to the ISG in MIN6 and human {beta}-cells. We further validate the role for one (SCAMP3) in regulating insulin storage and secretion from {beta}-cells for the first time. SCAMP3 knock-down INS-1 cells show a reduction in insulin content and dysfunctional insulin secretion. These data provide the basis for future investigation into {beta}-cell biology and the regulation of insulin secretion. Article HighlightsO_LIWhy did we undertake this study? We undertook this study to optimize insulin granule isolation techniques alongside enhanced proteomics analyses to establish the first published murine insulin granule proteome. C_LIO_LIWhat is the specific question(s) we wanted to answer? We aimed to specifically answer and investigate what proteins are present on insulin granules from MIN6 cells to further our understanding of insulin granule biogenesis, trafficking, and secretion. C_LIO_LIWhat did we find? We find and validate the presence of 5 novel insulin granule-associated proteins. C_LIO_LIWhat are the implications of our findings? An extensive proteomics analysis of MIN6 insulin granules and implicate Scamp3 as a novel protein that regulates insulin content and secretion in beta-cells. C_LI

cell biology↗

bioRxiv2021

Bacterial chemotaxis to saccharides is governed by a trade-off between sensing and uptake

To swim up gradients of nutrients, E. coli senses nutrient concentrations within its periplasm. For small nutrient molecules, periplasmic concentrations typically match extracellular concentrations. However, this is not necessarily the case for saccharides, such as maltose, which is transported into the periplasm via a specific porin. Previous observations have shown that under various conditions E. coli limits maltoporin abundance so that, for extracellular micromolar concentrations of maltose, there are predicted to be only nanomolar concentrations of free maltose in the periplasm. Thus, in the micromolar regime, the total uptake of maltose from the external environment into the cytoplasm is limited not by the abundance of cytoplasmic transport proteins but by the abundance of maltoporins. Here we present results from experiments and modeling showing that this porin-limited transport enables E. coli to sense micromolar gradients of maltose despite having a high-affinity ABC transport system that is saturated at these micromolar levels. We used microfluidic assays to study chemotaxis of E. coli in various gradients of maltose and methyl-aspartate and leveraged our experimental observations to develop a mechanistic transport-and-sensing chemotaxis model. Incorporating this model into agent-based simulations, we discover a trade-off between uptake and sensing: although high-affinity transport enables higher uptake rates at low nutrient concentrations, it severely limits dynamic sensing range. We thus propose that E. coli may limit periplasmic uptake to increase its chemotactic sensitivity, enabling it to use maltose as an environmental cue. Statement of SignificanceBacterial chemotaxis is among the best-studied systems in biology and is paradigmatic of the mechanisms used by cells to link sensory inputs with regulated responses, thus providing insight into the ecological basis of cellular physiology. Here we present a mechanistic chemotaxis model that describes how the regulation of the transport of a sugar into and out of the cells periplasm affects the cells motile response to that sugar. Based on observations from population-level chemotaxis assays, we uncover an ecologically relevant trade-off between sensing and uptake. The general finding of this work is that, while high-affinity transport allows for higher uptake rates, it can severely limit the cells dynamic sensing range.

microbiology↗

bioRxiv2021

The Induction of Pyrenoid Synthesis by Hyperoxia and its Implications for the Natural Diversity of Photosynthetic Responses in Chlamydomonas

In algae, it is well established that the pyrenoid, a component of the carbon-concentrating mechanism (CCM), is essential for efficient photosynthesis at low CO2. However, the signal that triggers the formation of the pyrenoid has remained elusive. Here, we show that, in Chlamydomonas reinhardtii, the pyrenoid is strongly induced by hyperoxia, even at high CO2 or bicarbonate levels. These results suggest that the pyrenoid can be induced by a common product of photosynthesis specific to low CO2 or hyperoxia. Consistent with this view, the photorespiratory by-product, H2O2, induced the pyrenoid, suggesting that it acts as a signal. Finally, we show evidence for linkages between genetic variations in hyperoxia tolerance, H2O2 signaling, and pyrenoid morphologies.

plant biology↗

bioRxiv2020

Mechanistic model of nutrient uptake explains dichotomy between marine oligotrophic and copiotrophic bacteria

Marine heterotrophic bacteria use a spectrum of nutrient uptake strategies, from that of copiotrophs--which dominate in nutrient-rich environments--to that of oligotrophs--which dominate in nutrient-poor environments. While copiotrophs possess numerous phosphotransferase systems (PTS), oligotrophs lack PTS and rely on ATP-binding cassette (ABC) transporters, which use binding proteins. Here we present a molecular-level model that explains the dichotomy between oligotrophs and copiotrophs as the consequence of trade-offs between PTS and ABC transport. When we approximate ABC transport in Michaelis-Menten form, we find, contrary to the canonical formulation, that its half-saturation concentration KM is not a constant but instead a function of binding protein abundance. Thus, oligotrophs can attain nanomolar KM values using binding proteins with micromolar dissociation constants and while closely matching transport and metabolic capacities. However, this requires large periplasms and high abundances of binding proteins, whose slow diffusion limits uptake rate. We conclude that the use of binding proteins is critical for oligotrophic survival yet severely constrains maximal growth rates, thus fundamentally shaping the divergent evolution of oligotrophs and copiotrophs.

microbiology↗