Enhanced SDC-assisted digestion coupled with lipid chromatography-tandem mass spectrometry for shotgun analysis of membrane proteome

Analysis of Host Cell Proteins in AAV Products with ProteoMiner Protein Enrichment Technology

Despite substantial efforts to detect host cell proteins (HCPs) in antibody drugs, information regarding HCPs in gene therapy products remains limited and has not been widely integrated into the host cell engineering or purification processes. Most methods that have successfully detected HCPs in antibody drugs are not applicable to gene therapy products, except for the ProteoMiner enrichment method. Here, we demonstrate that ProteoMiner beads effectively enrich HCPs in adeno-associated virus (AAV) products and simultaneously remove the detergent Pluronic F-68 without a loss of low-abundance HCPs. Following optimization of this technique, there was up to a 34-fold increase in the enrichment of HCPs compared to direct digestion. Moreover, the detection limit was significantly lowered with the ability to detect HCPs at levels as low as 0.1 ng/mL after ProteoMiner treatment. This approach holds promise in AAV HCP analysis and may be adaptable to other gene therapy products. The findings from this study provide valuable insights into HCPs in AAV products and may facilitate process development and host cell line optimization. The high sensitivity of this approach also facilitates detection of critical low-abundance HCPs, thereby contributing to risk assessment of their impact on the safety and quality of the AAV-based gene therapy products.

Ultrasensitive method for profiling host cell proteins by coupling limited digestion to ProteoMiner technology

Host cell proteins (HCPs) are process-related impurities that remain in therapeutic protein -at trace levels. HCPs must be closely monitored because they may be detrimental to drug product quality. Liquid chromatography coupled to mass spectrometry (LC-MS) is a powerful tool for detecting individual HCPs; however, HCP-derived peptides can be four to ten orders of magnitude less abundant than therapeutic protein-derived peptides in drug products, thus posing a major challenge in LC-MS detection. We previously demonstrated that low abundant HCPs can be enriched several hundreds fold through ProteoMiner. This study further improved the degree of enrichment by coupling limited digestion to ProteoMiner technology (PMLD). HCPs with low abundance were enriched 7694-fold, thus enabling detection of HCPs at concentrations as low as 0.002 ppm. A total of 850 HCPs were detected with high confidence from a NIST monoclonal antibody preparation, a number 40% higher than previously reported.

SimPLIT: Simplified Sample Preparation for Large-Scale Isobaric Tagging Proteomics

Large scale proteomic profiling of cell lines can reveal molecular signatures attributed to variable genotypes or induced perturbations, enabling proteogenomic associations and elucidation of pharmacological mechanisms of action. Although isobaric labeling has increased the throughput of proteomic analysis, the commonly used sample preparation workflows often require time-consuming steps and costly consumables, limiting their suitability for large scale studies. Here, we present a simplified and cost-effective one-pot reaction workflow in a 96-well plate format (SimPLIT) that minimizes processing steps and demonstrates improved reproducibility compared to alternative approaches. The workflow is based on a sodium deoxycholate lysis buffer and a single detergent cleanup step after peptide labeling, followed by quick off-line fractionation and MS2 analysis. We showcase the applicability of the workflow in a panel of colorectal cancer cell lines and by performing target discovery for a set of molecular glue degraders in different cell lines, in a 96-sample assay. Using this workflow, we report frequently dysregulated proteins in colorectal cancer cells and uncover cell-dependent protein degradation profiles of seven cereblon E3 ligase modulators (CRL4CRBN). Overall, SimPLIT is a robust method that can be easily implemented in any proteomics laboratory for medium-to-large scale TMT-based studies for deep profiling of cell lines.

Improved in-solution trypsin digestion method for methanol-chloroform precipitated cellular proteomics sample

Methanol-chloroform based protein precipitation is an essential step in many liquid chromatography-tandem mass spectrometry-based cellular proteomics applications. However, re-solubilization of the total protein precipitate is difficult using regular in-solution digestion protocol. Sodium deoxycholate is reported as an efficient surfactant for re-solubilization of membrane fractions. In this study, we demonstrated an application combining methanol-chloroform based protein precipitations and deoxycholic acid assisted re-solubilization of pellets to evaluate the improvement of protein identifications in mass spectrometry-based bottom-up proteomics. We evaluated the modified method using an equal amount of Raw 264.7 mouse macrophage cell lysate. Detailed in-solution trypsin digestion studies were presented on methanol-chloroform precipitated samples with or without deoxycholic acid treatments and compared with popular sample digestion methods. A mass spectrometric analysis confirmed an 82% increase in protein identification in deoxycholic acid-treated samples compared to other established methods. Furthermore, liquid chromatography-tandem mass spectrometry analysis of an equal amount of proteins from methanol-chloroform precipitated, and methanol-chloroform/deoxycholic acid-treated macrophage cell lysate showed a 14% increase and 27% unique protein identifications. We believe this improved digestion method could be a complementary or alternative method for mammalian cell sample preparations where sodium dodecyl sulfate based lysis buffer is frequently used.

Evaluation of sodium deoxycholate as solubilization buffer for oil palm proteomics analysis

Protein solubility is a critical prerequisite to any proteomics analysis. Combination of urea/thiourea and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) have been routinely used to enhance protein solubilization for oil palm proteomics studies in recent years. The goals of these proteomics analysis are essentially to complement the knowledge regarding the regulation networks and mechanisms of the oil palm fatty acid biosynthesis. Through omics integration, the information is able to build a regulatory model to support efforts in improving the economic value and sustainability of palm oil in the global oil and vegetable market. Our study evaluated the utilization of sodium deoxycholate as an alternative solubilization buffer/additive to urea/thiourea and CHAPS. Efficiency of urea/thiourea/CHAPS, urea/CHAPS, urea/sodium deoxycholate and sodium deoxycholate buffers in solubilizing the oil palm (Elaeis guineensis var. Tenera) mesocarp proteins were compared. Based on the protein yields and electrophoretic profile, combination of urea/thiourea/CHAPS were shown to remain a better solubilization buffer and additive, but the differences with sodium deoxycholate buffer was insignificant. A deeper mass spectrometric and statistical analyses on the identified proteins and peptides from all the evaluated solubilization buffers revealed that sodium deoxycholate had increased the number of identified proteins from oil palm mesocarps, enriched their gene ontologies and reduced the number of carbamylated lysine residues by more than 67.0%, compared to urea/thiourea/CHAPS buffer. Although only 62.0% of the total identified proteins were shared between the urea/thiourea/CHAPS and sodium deoxycholate buffers, the importance of the remaining 38.0% proteins depends on the applications. The only observed limitations to the application of sodium deoxycholate in protein solubilization were the interference with protein quantitation and but it could be easily rectified through a 4-fold dilution. All the proteomics data are available via ProteomeXchange with identifier PXD013255. In conclusion, sodium deoxycholate is applicable in the solubilization of proteins extracted from oil palm mesocarps with higher efficiency compared to urea/thiourea/CHAPS buffer. The sodium deoxycholate buffer is more favorable for proteomics analysis due to its proven advantages over urea/thiourea/CHAPS buffer.

Straightforward Protocol for Gel-Free Proteomic Analysis of Adipose Tissue

After conducting systematic and quantitative comparisons of different sample preparation techniques regarding their capability to efficiently and reproducibly recover proteins from biopsies, we present here our superior protocol for extracting proteins from low amounts of adipose tissue. Adipose tissue as a matrix in bottom-up proteomics is challenging due to the extremely high lipid content.The lysis buffer utilized contains the detergent sodium deoxycholate, which does not impair the activity of trypsin and therefore enables direct digestion without detergent removal steps. The resulting workflow is time saving, cost efficient, easy to perform, and it can also be applied to other hydrophobic samples.

Seizure protein 6 and its homolog seizure 6-like protein are physiological substrates of BACE1 in neurons

Background

The protease BACE1 (beta-site APP cleaving enzyme) is a major drug target in Alzheimer’s disease. However, BACE1 therapeutic inhibition may cause unwanted adverse effects due to its additional functions in the nervous system, such as in myelination and neuronal connectivity. Additionally, recent proteomic studies investigating BACE1 inhibition in cell lines and cultured murine neurons identified a wider range of neuronal membrane proteins as potential BACE1 substrates, including seizure protein 6 (SEZ6) and its homolog SEZ6L.

Methods and results

We generated antibodies against SEZ6 and SEZ6L and validated these proteins as BACE1 substrates in vitro and in vivo. Levels of the soluble, BACE1-cleaved ectodomain of both proteins (sSEZ6, sSEZ6L) were strongly reduced upon BACE1 inhibition in primary neurons and also in vivo in brains of BACE1-deficient mice. BACE1 inhibition increased neuronal surface levels of SEZ6 and SEZ6L as shown by cell surface biotinylation, demonstrating that BACE1 controls surface expression of both proteins. Moreover, mass spectrometric analysis revealed that the BACE1 cleavage site in SEZ6 is located in close proximity to the membrane, similar to the corresponding cleavage site in SEZ6L. Finally, an improved method was developed for the proteomic analysis of murine cerebrospinal fluid (CSF) and was applied to CSF from BACE-deficient mice. Hereby, SEZ6 and SEZ6L were validated as BACE1 substrates in vivo by strongly reduced levels in the CSF of BACE1-deficient mice.

Conclusions

This study demonstrates that SEZ6 and SEZ6L are physiological BACE1 substrates in the murine brain and suggests that sSEZ6 and sSEZ6L levels in CSF are suitable markers to monitor BACE1 inhibition in mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0134-z) contains supplementary material, which is available to authorized users.

Glycomics and glycoproteomics of membrane proteins and cell-surface receptors: Present trends and future opportunities

Membrane proteins mediate cell-cell interactions and adhesion, the transfer of ions and metabolites, and the transmission of signals from the extracellular environment to the cell interior. The extracellular domains of most cell membrane proteins are glycosylated, often at multiple sites. There is a growing awareness that glycosylation impacts the structure, interaction, and function of membrane proteins. The application of glycoproteomics and glycomics methods to membrane proteins has great potential. However, challenges also arise from the unique physical properties of membrane proteins. Successful analytical workflows must be developed and disseminated to advance functional glycoproteomics and glycomics studies of membrane proteins. This review explores the opportunities and challenges related to glycomic and glycoproteomic analysis of membrane proteins, including discussion of sample preparation, enrichment, and MS/MS analyses, with a focus on recent successful workflows for analysis of N- and O-linked glycosylation of mammalian membrane proteins.