Isolation of Neuronal Synaptic Membranes by Sucrose Gradient Centrifugation

Sucrose gradient centrifugation is a very useful technique for isolating specific membrane types based on their size and density. This is especially useful for detecting fatty acids and lipid molecules that are targeted to specialized membranes. Without fractionation, these types of molecules could be below the levels of detection after being diluted out by the more abundant lipid molecules with a more ubiquitous distribution throughout the various cell membranes. Isolation of specific membrane types where these lipids are concentrated allows for their detection and analysis. We describe herein our synaptic membrane isolation protocol that produces excellent yield and clear resolution of five major membrane fractions from a starting neural tissue homogenate: P1 (nuclear), P2 (cytoskeletal), P3 (neurosynaptosomal), PSD (post-synaptic densities), and SV (synaptic vesicle).

The effect of organic matter fractions on micropollutant ozonation in wastewater effluents

Organic matter (OM) is the most important factor influencing the effectivity and efficiency of micropollutant (MP) ozonation in wastewater effluents. The importance of the quantity of OM is known, because of this, total organic carbon (TOC) is generally used to determine the required ozone dose for any water sample. Still, the effect of OM type on MP ozonation is not well understood. In this study, effluents from five wastewater treatment plants were collected and the organic matter in these effluents was fractionated using membranes (F1-4) and resin (HI, HOA, HON and HOB). Fractions were diluted to the same TOC concentration, spiked with MPs and ozonated at three ozone doses. Our results show that all five effluents had comparable OM compositions and similar MP removal, confirming the suitability of OM quantity (TOC) to compare the ozone requirements for wastewater effluents. From the 19 analysed MPs, three groups were identified that showed similar removal behaviour. The strongest differences between the groups were observed around MP ozone reactivities of 10², 10⁴ and 10⁶ M^-1 s^-1. This indicates the presence of three OM groups in the samples that interfere with the removal of different MPs. MP removal in the resin fraction HON were higher for MPs with high and medium ozone reactivity, indicating a low interference of OM in this fraction with MP ozonation. OM in the resin fractions HOA and HI showed higher interference with MP ozonation. Therefore, removing the HOA and HI fractions prior to ozonation would result in a lower required ozone dose and a more efficient removal of the MPs. MP removal correlated with the OM characteristics A300, SR and fluorescence component comp 2. These characteristics can be used as inline tools to predict the required ozone dose in water treatment plants.

Membrane Fractionation by Isopycnic Sucrose Density Gradient Centrifugation for Qualitative Analysis of LPS in Escherichia coli

Gram-negative diderm bacteria are characterized by a tripartite cell envelope, composed of an inner membrane (IM) and a lipopolysaccharide (LPS)-containing outer membrane (OM), separated by an aqueous space where the peptidoglycan is embedded. LPS is a peculiar glycolipid endowed with several biological activities. The biosynthesis and transport of LPS to its final location take place in every compartment of the cell envelope. Proteins and protein machineries with different subcellular localization are involved in this process to facilitate the trafficking of LPS across subcellular compartments that differ in their physicochemical proprieties. The fractionation of bacterial cell envelopes can give information on the status of the LPS biogenesis by allowing the analysis of LPS profiles and of the localization of proteins involved in the transport. Here, we describe a standardized protocol for membrane fractionation in Escherichia coli using sucrose density gradient centrifugation that separates the IM from the OM cellular fractions. Bacterial cells are first converted into spheroplasts and lysed; then the membrane fractions are collected by ultracentrifugation and separated at high speed by exploiting the differences in membrane density. The fractions obtained are analyzed for LPS total amount and electrophoretic profile.

Differential Detergent Fractionation of Membrane Protein From Small Samples of Hepatocytes and Liver Tissue for Quantitative Proteomic Analysis of Drug Metabolizing Enzymes and Transporters

The fractionation of enough membrane protein from limited samples is challenging for MS-based quantitative targeted absolute proteomics (QTAP) of drug metabolizing enzymes (DMEs) and transporters. This study evaluated differential detergent fractionation (DDF) of membrane protein from progressively smaller numbers of primary mouse hepatocytes (5 million down to 50,000 cells) and limited liver tissue (25-50 mg) in quantifying select DMEs and transporters by QTAP. Two non-ionic detergents, digitonin and Triton-X-100, were applied in sequence to permeabilize cells and extract membrane proteins. Comparison was made with a membrane protein extraction kit and with homogenization in hypotonic buffer and subsequent differential centrifugation (DC). DDF produced linear membrane protein yields with increasing hepatocyte numbers and better permeabilization evidenced by the higher ratio of cytosolic to membrane protein yields. DDF produced 5-times more membrane protein from liver tissue than DC. The concentration of DMEs and transporters remained consistent in the fractions prepared by DDF from progressively smaller numbers of hepatocytes, but declined in kit fractions. In liver tissue, the concentrations were comparatively higher in DDF versus kit and DC. In conclusion, sequential digitonin and Triton-X-100 fractionation of membrane protein from limited samples is efficient, reproducible and cost-effective for QTAP of DMEs and transporters.

Valorisation of tuna processing waste biomass: isolation, purification and characterisation of four novel antioxidant peptides from tuna by-product hydrolysate

Tuna protein hydrolysate (TPH) was prepared by hydrolysis with Prolyve BS and fractionated by membranes process. The antioxidant activities of recovered peptide fractions were evaluated. Four novel antioxidant peptides that were isolated from nanofiltration retentate exhibited the highest antioxidant activity, using gel chromatography and reversed phase high-performance liquid chromatography. The amino acid sequences of isolated peptides were identified as Tyr-Glu-Asn-Gly-Gly (P2), Glu-Gly-Tyr-Pro-Trp-Asn (P4), Tyr-Ile-Val-Tyr-Pro-Gly (P7) and Trp-Gly-Asp-Ala-Gly-Gly-Tyr-Tyr (P8) with molecular weights of 538.46, 764.75, 710.78 and 887.85 Da, respectively. P2, P4, P7 and P8 exhibited good scavenging activities on hydroxyl radical (IC₅₀ 0.41, 0.327, 0.17 and 0.042 mg/ml), DPPH radical (IC₅₀ 0.666, 0.326, 0.451 and 0.377 mg/ml) and superoxide radical (IC₅₀ 0.536, 0.307, 0.357 and 0.115 mg/ml). P7 was effective against lipid peroxidation in the model system. The isolated peptides might be useful used as natural food additive in food industry and formulation of nutritional products.

Isolation of Neuronal Synaptic Membranes by Sucrose Gradient Centrifugation

Sucrose gradient centrifugation is a very useful technique for isolating specific membrane types based on their size and density. This is especially useful for detecting fatty acids and lipid molecules that are targeted to specialized membranes. Without fractionation, these types of molecules could be below the levels of detection after being diluted out by the more abundant lipid molecules with a more ubiquitous distribution throughout the various cell membranes. Isolation of specific membrane types where these lipids are concentrated allows for their detection and analysis. We describe herein our synaptic membrane isolation protocol that produces excellent yield and clear resolution of five major membrane fractions from a starting neural tissue homogenate: P1 (Nuclear), P2 (Cytoskeletal), P3 (Neurosynaptosomal), PSD (Post-synaptic Densities), and SV (Synaptic Vesicle).

Preparation of Gap Junctions in Membrane Microdomains for Immunoprecipitation and Mass Spectrometry Interactome Analysis

Protein interaction networks at gap junction plaques are increasingly implicated in a variety of intracellular signaling cascades. Identifying protein interactions of integral membrane proteins is a valuable tool for determining channel function. However, several technical challenges exist. Subcellular fractionation of the bait protein matrix is usually required to identify less abundant proteins in complex homogenates. Sufficient solvation of the lipid environment without perturbation of the protein interactome must also be achieved. The present chapter describes the flotation of light and heavy liver tissue membrane microdomains to facilitate the identification and analysis of endogenous gap junction proteins and includes technical notes for translation to other integral membrane proteins, tissues, or cell culture models. These procedures are valuable tools for the enrichment of gap junction membrane compartments and for the identification of gap junction signaling interactomes.

Analysis of photosystem II biogenesis in cyanobacteria

Photosystem II (PSII), a large multisubunit membrane protein complex found in the thylakoid membranes of cyanobacteria, algae and plants, catalyzes light-driven oxygen evolution from water and reduction of plastoquinone. Biogenesis of PSII requires coordinated assembly of at least 20 protein subunits, as well as incorporation of various organic and inorganic cofactors. The stepwise assembly process is facilitated by numerous protein factors that have been identified in recent years. Further analysis of this process requires the development or refinement of specific methods for the identification of novel assembly factors and, in particular, elucidation of the unique role of each. Here we summarize current knowledge of PSII biogenesis in cyanobacteria, focusing primarily on the impact of methodological advances and innovations. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Conrad Mullineaux.