An official website of the United States government
Organelle pH is critical to organelle identity and function. Resident proteins that define each organelle modify transiting cargo proteins, with both retention and trafficking between organelles governed by pH-dependent mechanisms. For example, lysosomal enzymes bind mannose-6-phosphate receptors at the higher pH (∼6.5) of the Golgi and dissociate at the lower pH (∼5.5) of late endosomes1. Proteins that stray from the endoplasmic reticulum (ER) are captured by KDEL receptors in the acidic Golgi and returned into the neutral ER2,3. This pH-tuned trafficking system compartmentalizes organelle function and prevents mis-localization of critical enzymes4. Dysregulated organelle pH disrupts their function and leads to various diseases. Because protons move rapidly in water, the pH within a single organelle is currently assumed to be spatially uniform5. Here, using a reporter sensitive from pH 5.5 - 10.5 to map a spectrum of organelles at high resolution, we discovered that pH gradients exist within single, large or long organelles such as the ER and mitochondria, and in membrane-less organelles without ion-transporting proteins such as the nucleolus. These new findings upend our understanding of organellar pH, prompting new questions about proton diffusion within the cell, and its potential consequences on organelle function.
more »
« less
This content will become publicly available on January 20, 2027
Organelles harbour pH gradients
Abstract Organelle pH is critical to organelle identity and function. Resident proteins that define each organelle modify transiting cargo proteins, with both retention and trafficking between organelles governed by pH-dependent mechanisms. For example, lysosomal enzymes bind mannose-6-phosphate receptors at the higher pH (~6.5) of the Golgi and dissociate at the lower pH (~5.5) of late endosomes. Proteins that stray from the endoplasmic reticulum (ER) are captured by KDEL receptors in the acidic Golgi and returned into the neutral ER. This pH-tuned trafficking system compartmentalizes organelle function and prevents mis-localization of critical enzymes. Dysregulated organelle pH disrupts their function and leads to various diseases. Because protons move rapidly in water, the pH within a single organelle is currently assumed to be spatially uniform. Here, using a reporter sensitive from pH 5.5 - 10.5 to map a spectrum of organelles at high resolution, we discovered that pH gradients exist within single, large or long organelles such as the ER and mitochondria, and in membrane-less organelles without ion-transporting proteins such as the nucleolus. These new findings upend our understanding of organellar pH, prompting new questions about proton diffusion within the cell, and its potential consequences on organelle function.
more »
« less
- Award ID(s):
- 2121044
- PAR ID:
- 10679740
- Publisher / Repository:
- Research Square
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Cell organelles feature characteristic lipid compositions that lead to differences in membrane properties. In living cells, membrane ordering and fluidity are commonly measured using the solvatochromic dye Laurdan, whose fluorescence is sensitive to membrane packing. As a general lipophilic dye, Laurdan stains all hydrophobic environments in cells, so it is challenging to characterize membrane properties in specific organelles or assess their responses to pharmacological treatments in intact cells. Here, we describe the synthesis and application of Laurdan-derived probes that read out membrane packing of individual cellular organelles. The set of Organelle-targeted Laurdans (OTL) localizes to the ER, mitochondria, lysosomes and Golgi compartments with high specificity, while retaining the spectral resolution needed to detect biological changes in membrane packing. We show that ratiometric imaging with OTL can resolve membrane heterogeneity within organelles, as well as changes in membrane packing resulting from inhibition of lipid trafficking or bioenergetic processes. We apply these probes to characterize organelle-specific responses to saturated lipid stress. While ER and lysosomal membrane fluidity is sensitive to exogenous saturated fatty acids, that of mitochondrial membranes is protected. We then use differences in ER membrane fluidity to sort populations of cells based on their fatty acid diet, highlighting the ability of organelle-localized solvatochromic probes to distinguish between cells based on their metabolic state. These results expand the repertoire of targeted membrane probes and demonstrate their application to interrogating lipid dysregulation.more » « less
-
Abstract Endomembrane trafficking is essential for all eukaryotic cells. The best-characterized membrane trafficking organelles include the endoplasmic reticulum (ER), Golgi apparatus, early and recycling endosomes, multivesicular body, or late endosome, lysosome/vacuole, and plasma membrane. Although historically plants have given rise to cell biology, our understanding of membrane trafficking has mainly been shaped by the much more studied mammalian and yeast models. Whereas organelles and major protein families that regulate endomembrane trafficking are largely conserved across all eukaryotes, exciting variations are emerging from advances in plant cell biology research. In this review, we summarize the current state of knowledge on plant endomembrane trafficking, with a focus on four distinct trafficking pathways: ER-to-Golgi transport, endocytosis, trans-Golgi network-to-vacuole transport, and autophagy. We acknowledge the conservation and commonalities in the trafficking machinery across species, with emphasis on diversity and plant-specific features. Understanding the function of organelles and the trafficking machinery currently nonexistent in well-known model organisms will provide great opportunities to acquire new insights into the fundamental cellular process of membrane trafficking.more » « less
-
Abstract Plants continuously remodel and degrade their organelles due to damage from their metabolic activities and environmental stressors, as well as an integral part of their cell differentiation programs. Whereas certain organelles use local hydrolytic enzymes for limited remodeling, most of the pathways that control the partial or complete dismantling of organelles rely on vacuolar degradation. Specifically, selective autophagic pathways play a crucial role in recognizing and sorting plant organelle cargo for vacuolar clearance, especially under cellular stress conditions induced by factors like heat, drought, and damaging light. In these short reviews, we discuss the mechanisms that control the vacuolar degradation of chloroplasts, mitochondria, endoplasmic reticulum, Golgi, and peroxisomes, with an emphasis on autophagy, recently discovered selective autophagy receptors for plant organelles, and crosstalk with other catabolic pathways.more » « less
-
Abstract Proper regulation of organelle dynamics and inter-organelle contacts is critical for cellular health and function. Both the endoplasmic reticulum (ER) and actin cytoskeleton are known to regulate organelle dynamics, but how, when, and where these two subcellular components are coordinated to control organelle dynamics remains unclear. Here, we show that ER-associated actin consistently marks mitochondrial, endosomal, and lysosomal fission sites. We also show that actin polymerization by the ER-anchored isoform of the formin protein INF2 is a key regulator of the morphology and mobility of these organelles. Together, our findings establish a mechanism by which INF2-mediated polymerization of ER-associated actin at ER-organelle contacts regulates organelle dynamics.more » « less
