Structural insights into how vacuolar sorting receptors recognize the sorting determinants of seed storage proteins

In Arabidopsis, vacuolar sorting receptor isoform 1 (VSR1) sorts 12S globulins to the protein storage vacuoles during seed development. Vacuolar sorting is mediated by specific protein–protein interactions between VSR1 and the vacuolar sorting determinant located at the C terminus (ctVSD) on the cargo proteins. Here, we determined the crystal structure of the protease-associated domain of VSR1 (VSR1-PA) in complex with the C-terminal pentapeptide (468RVAAA472) of cruciferin 1, an isoform of 12S globulins. The 468RVA470 motif forms a parallel β-sheet with the switch III residues (127TMD129) of VSR1-PA, and the 471AA472 motif docks to a cradle formed by the cargo-binding loop (95RGDCYF100), making a hydrophobic interaction with Tyr99. The C-terminal carboxyl group of the ctVSD is recognized by forming salt bridges with Arg95. The C-terminal sequences of cruciferin 1 and vicilin-like storage protein 22 were sufficient to redirect the secretory red fluorescent protein (spRFP) to the vacuoles in Arabidopsis protoplasts. Adding a proline residue to the C terminus of the ctVSD and R95M substitution of VSR1 disrupted receptor–cargo interactions in vitro and led to increased secretion of spRFP in Arabidopsis protoplasts. How VSR1-PA recognizes ctVSDs of other storage proteins was modeled. The last three residues of ctVSD prefer hydrophobic residues because they form a hydrophobic cluster with Tyr99 of VSR1-PA. Due to charge–charge interactions, conserved acidic residues, Asp129 and Glu132, around the cargo-binding site should prefer basic residues over acidic ones in the ctVSD. The structural insights gained may be useful in targeting recombinant proteins to the protein storage vacuoles in seeds.

FPCount protocol - Full protocol v1

FPCount is a complete protocol for fluorescent protein calibration, consisting of: 1. FP expression/purification using Thermo's HisPur Cobalt Resin. 2. FP concentration determination in a microplate reader. 3. FP fluorescence quantification in a microplate reader. Results can be analysed with the corresponding R package, FPCountR. --- Summary 1. Expression 2. Harvesting/Washing 3. Lysis 4. Fractionation 5. Gel1: Verification of Expression/Fractions 6. Purification 7. Gel2: Verification of Purification 8. Protein concentration and buffer exchange 9. Quantification of FP concentration (part1) 10. Quantification of FP fluorescence 11. Quantification of FP concentration (part2) 12. Protein Storage 13. Calibration of Plate Reader

FPCount protocol - in-lysate (purification free) protocol v1

FPCount is a complete protocol for fluorescent protein calibration, consisting of: 1. FP expression and production of cell lysates. 2. FP concentration determination in a microplate reader. 3. FP fluorescence quantification in a microplate reader. Results can be analysed with the corresponding R package, FPCountR. This in-lysate version of the protocol uses the ECmax protein quantification protocol of FPs in lysates and does not require His-tag purification of the FPs. Note that it is only suitable for FPs with entries in FPbase. If you want to verify or validate results, it's recommended you follow the 'short' protocol, which requires FP purification, or the 'complete' protocol, which requires FP purification and compares three protein quantification methods. --- Summary 1. Expression 2. Harvesting/Washing 3. Lysis 4. Fractionation 8. Protein concentration and buffer exchange 9. Quantification of FP concentration (part1) 10. Quantification of FP fluorescence 12. Protein storage 13. Calibration of Plate Reader

FPCount protocol - Short protocol v1

FPCount is a complete protocol for fluorescent protein calibration, consisting of: 1. FP expression/purification using Thermo's HisPur Cobalt Resin. 2. FP concentration determination in a microplate reader. 3. FP fluorescence quantification in a microplate reader. Results can be analysed with the corresponding R package, FPCountR. This short version uses the ECmax protein quantification protocol, and is only suitable for FPs with entries in FPbase. If you want to verify or validate results, it's recommended you follow the complete protocol, which describes three protein quantification methods. The short protocol also skips the SDS-PAGE steps. If you require these, please see the complete protocol. --- Summary 1. Expression 2. Harvesting/Washing 3. Lysis 4. Fractionation 6. Purification 8. Protein concentration and buffer exchange 9. Quantification of FP concentration (part1) 10. Quantification of FP fluorescence 12. Protein storage 13. Calibration of Plate Reader

Abiotic Stress Triggers the Expression of Genes Involved in Protein Storage Vacuole and Exocyst-Mediated Routes

Adverse conditions caused by abiotic stress modulate plant development and growth by altering morphological and cellular mechanisms. Plants’ responses/adaptations to stress often involve changes in the distribution and sorting of specific proteins and molecules. Still, little attention has been given to the molecular mechanisms controlling these rearrangements. We tested the hypothesis that plants respond to stress by remodelling their endomembranes and adapting their trafficking pathways. We focused on the molecular machinery behind organelle biogenesis and protein trafficking under abiotic stress conditions, evaluating their effects at the subcellular level, by looking at ultrastructural changes and measuring the expression levels of genes involved in well-known intracellular routes. The results point to a differential response of the endomembrane system, showing that the genes involved in the pathway to the Protein Storage Vacuole and the exocyst-mediated routes are upregulated. In contrast, the ones involved in the route to the Lytic Vacuole are downregulated. These changes are accompanied by morphological alterations of endomembrane compartments. The data obtained demonstrate that plants’ response to abiotic stress involves the differential expression of genes related to protein trafficking machinery, which can be connected to the activation/deactivation of specific intracellular sorting pathways and lead to alterations in the cell ultrastructure.

Protein reservoirs of seeds are composites of amyloid and amyloid-like structures

Seed storage proteins, well-known for their nutritional functions are sequestered in protein bodies. However, their biophysical properties at the molecular level remain elusive. Based on the structure and function of protein bodies found in other organisms, we hypothesize that the seed protein bodies might be present as amyloid structures. When visualized with a molecular rotor Thioflavin-T and a recently discovered Proteostat® probe with enhanced sensitivity, the seed sections showed amyloid-like signatures in the protein storage bodies of the aleurone cells of monocots and cotyledon cells of dicots. To make the study compliant for amyloid detection, gold-standard Congo red dye was used. Positive apple-green birefringence due to Congo red affinity in some of the areas of ThT and Proteostat® binding, suggests the presence of both amyloid-like and amyloid deposits in the protein storage bodies. Further, diminishing amyloid signature in germinating seeds implies the degradation of these amyloid structures and their utilization. This study will open new research avenues for a detailed molecular-level understanding of the formation and utilization of aggregated protein bodies as well as their evolutionary roles.

The Trafficking Machinery of Lytic and Protein Storage Vacuoles: How Much is Shared and How Much is Distinct?

Plant cells contain two types of vacuoles, the lytic vacuole and the protein storage vacuole. Lytic vacuoles (LVs) are present in vegetative cells, whereas protein storage vacuoles (PSVs) are found in seed cells. The physiological functions of the two vacuole types differ. Newly synthesized proteins must be transported to these vacuoles via protein trafficking through the endomembrane system for them to function. Recently, significant advances have been made in elucidating the molecular mechanisms of protein trafficking to these organelles. Despite these advances, the relationship between the trafficking mechanisms in LV and PSVs remains unclear. Some aspects of the trafficking mechanisms are common to both organelles, but certain aspects are specific to trafficking to either LV or PSVs. In this review, we summarize recent findings on the components involved in protein trafficking to both LV and PSVs and compare them to examine the extent of overlap in the trafficking mechanisms. In addition, we discuss the interconnection between the LV and PSVs in protein trafficking machinery and the implication in the identity of these organelles.

Amyloid proteins of plants and microorganisms: biological functions and participation in the formation of supra-organismal systems

Here we will review the latest advances in the study of functional amyloids of plants and symbiotic bacteria demonstrating the involvement of these protein fibrils in protein storage in plant seeds and formation of supra-organismal interactions.

Expression of a Hyperthermophilic Cellobiohydrolase in Transgenic Nicotiana tabacum by Protein Storage Vacuole Targeting

Plant expression of microbial Cell Wall Degrading Enzymes (CWDEs) is a valuable strategy to produce industrial enzymes at affordable cost. Unfortunately, the constitutive expression of CWDEs may affect plant fitness to variable extents, including developmental alterations, sterility and even lethality. In order to explore novel strategies for expressing CWDEs in crops, the cellobiohydrolase CBM3GH5, from the hyperthermophilic bacterium Caldicellulosiruptor saccharolyticus, was constitutively expressed in N. tabacum by targeting the enzyme both to the apoplast and to the protein storage vacuole. The apoplast targeting failed to isolate plants expressing the recombinant enzyme despite a large number of transformants being screened. On the opposite side, the targeting of the cellobiohydrolase to the protein storage vacuole led to several transgenic lines expressing CBM3GH5, with an enzyme yield of up to 0.08 mg g DW−1 (1.67 Units g DW−1) in the mature leaf tissue. The analysis of CBM3GH5 activity revealed that the enzyme accumulated in different plant organs in a developmental-dependent manner, with the highest abundance in mature leaves and roots, followed by seeds, stems and leaf ribs. Notably, both leaves and stems from transgenic plants were characterized by an improved temperature-dependent saccharification profile.