Sep 01, 2025

Public workspaceTurboID-phosphoenrichment workflow protocol

  • Jasmin Jansen1,2,3
  • 1University of Konstanz, Department of Biology;
  • 2Aligning Science Across Parkinson's Disease;
  • 3Konstanz Research School of Chemical Biology (KoRS-CB)
Icon indicating open access to content
QR code linking to this content
Protocol CitationJasmin Jansen 2025. TurboID-phosphoenrichment workflow protocol. protocols.io https://dx.doi.org/10.17504/protocols.io.ewov1drpyvr2/v1
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License,  which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it has worked in our previous experiments.
Created: March 04, 2025
Last Modified: September 01, 2025
Protocol Integer ID: 123769
Keywords: ASAPCRN, TurboID, Phosphoenrichment, quantitative proteomics, DIA-MS, phosphoproteomics, phosphopeptide enrichment to mass spectrometric analysis, rich repeat kinase, phosphosites of this interactome, wide interactomes of leucine, phosphopeptide enrichment, phosphorylation activity, phosphorylation, cell culture over turboid, mass spectrometric analysis, changed phosphosite, streptavidin enrichment, based phosphoenrichment, proteome, comprehensive dataset of interactor, wide interactome, interactome
Funders Acknowledgements:
Aligning Science Across Parkinson’s (ASAP)
Grant ID: ASAP-000519
German Research Foundation
Grant ID: 496470458
German Research Foundation
Grant ID: 516836828
Abstract
This protocol is meant to accompany the manuscript "Probing the proteome-wide interactomes of Leucine-rich Repeat Kinases 1 and 2 and alterations in their phosphorylation activity" and its methods section.
The protocol describes all steps of the experimental workflow starting from cell culture over TurboID, streptavidin enrichment and phosphopeptide enrichment to mass spectrometric analysis using Data-Independent acquisition (DIA)-based quantification and data analysis.

The aim is to get a comprehensive dataset of interactors together with changed phosphosites of this interactome based on TurboID (Cho et al., 2020) and TiO2-based phosphoenrichment.

All steps are described per sample.
Guidelines
When preparing samples for mass spectrometry, work carefully, always wear appropriate gloves to minimize sample contamination that impedes your analysis. For downstream applications like mass spectrometry, it is crucial to wash cell pellets carefully to minimize protein contamination through fetal bovine serum.

For cell culture, please check your cell line(s) routinely for mycoplasma and other contaminations to avoid artefacts introduced thereby.
Materials
ReagentAnti-LRRK2 (phospho S935) antibody [UDD2 10(12)]AbcamCatalog #ab133450 ReagentPrimary Antibody anti-LRRK2 c41-2 AbcamCatalog #ab133474 ReagentLactic acid solution, 85 %Merck MilliporeSigma (Sigma-Aldrich)Catalog #252476 ReagentGlycolic acidMerck MilliporeSigma (Sigma-Aldrich)Catalog #124737 ReagentTitansphere TiO, 5 μm, 500 mgGL ScienceCatalog #020-75000 ReagentSequencing Grade Modified TrypsinPromegaCatalog #V5113

Equipment
Pierce™ C18-Spin columns
NAME
C18 column
TYPE
Pierce
BRAND
84850
SKU
LINK
ReagentTrypsin/Lys-C Mix, Mass Spec Grade, 5 x 20ugPromegaCatalog #V5073 ReagentIodoacetamideMerck MilliporeSigma (Sigma-Aldrich)Catalog #I1149-5G ReagentTris(2-carboxyethyl)phosphin -hydrochloridMerck MilliporeSigma (Sigma-Aldrich)Catalog #C4706 ReagentPierce™ Streptavidin Magnetic BeadsThermo FisherCatalog #88817 ReagentcOmplete™, EDTA-free protease inhibitor cocktailRocheCatalog #11873580001 ReagentFormaldehyede 37% solutionCarl RothCatalog #7398 ReagentDulbeccos Phosphate-buffered salineGibco - Thermo Fisher ScientificCatalog #21300058 ReagentIN04AOBIOUS IncCatalog #AOB13355 ReagentMLi-2Merck MilliporeSigma (Sigma-Aldrich)Catalog #SML3101 ReagentBiotinMerck MilliporeSigma (Sigma-Aldrich)Catalog #B4639 ReagentPolyethylenimine, Linear, MW 25000, Transfection GradePolysciences, Inc.Catalog #23966 ReagentOpti-MEM™ I Reduced Serum MediumThermo FisherCatalog #31985070 ReagentDulbeccos modified eagle medium (DMEM), high glucoseGibco - Thermo Fisher ScientificCatalog #41965062
ReagentFetal bovine serum (FBS) SuperiorMerck MilliporeSigma (Sigma-Aldrich)Catalog #S0615
ReagentDMSOSupelcoCatalog #1.09678.0100 ReagentHRP Anti-Rabbit IgGDianovaCatalog #AKC080 ReagentAnti-RAB10 (phospho T73) antibody [MJF-R21]AbcamCatalog #ab230261 ReagentRecombinant Anti-RAB10 antibody [MJF-R23]AbcamCatalog #ab237703
ReagentHiPPR™ Detergent Removal Spin Column KitThermo FisherCatalog #88305 ReagentSep-Pak tC18 1 cc Vac Cartridge 50 mg Sorbent per CartridgeWatersCatalog #WAT054960 Reagent3M™ Empore™ C18 47 mm Extraction Disc Model 2215 20 pack 3 packs per case3M corporationCatalog #2215
ReagentAcclaim™ PepMap™ 100 C18 HPLC ColumnsThermo ScientificCatalog #164945



Equipment
Concentrator Plus
NAME
Centrifugal vacuum concentrator
TYPE
Eppendorf
BRAND
5305000568
SKU
LINK


Protocol materials
ReagentDulbeccos modified eagle medium (DMEM), high glucoseGibco - Thermo Fisher ScientificCatalog #41965062
ReagentFetal bovine serum (FBS) SuperiorMerck MilliporeSigma (Sigma-Aldrich)Catalog #S0615
ReagentDulbeccos Phosphate-buffered salineGibco - Thermo Fisher ScientificCatalog #21300058
ReagentFormaldehyede 37% solutionCarl RothCatalog #7398
ReagentBiotinMerck MilliporeSigma (Sigma-Aldrich)Catalog #B4639
ReagentcOmplete™, EDTA-free protease inhibitor cocktailRocheCatalog #11873580001
ReagentTris(2-carboxyethyl)phosphin -hydrochloridMerck MilliporeSigma (Sigma-Aldrich)Catalog #C4706
ReagentIodoacetamideMerck MilliporeSigma (Sigma-Aldrich)Catalog #I1149-5G
ReagentTrypsin/Lys-C Mix, Mass Spec Grade, 5 x 20ugPromegaCatalog #V5073
ReagentHiPPR™ Detergent Removal Spin Column KitThermo FisherCatalog #88305
ReagentAcclaim™ PepMap™ 100 C18 HPLC ColumnsThermo ScientificCatalog #164945
ReagentRecombinant Anti-RAB10 antibody [MJF-R23]AbcamCatalog #ab237703
Reagent3M™ Empore™ C18 47 mm Extraction Disc Model 2215 20 pack 3 packs per case3M corporationCatalog #2215
ReagentGlycolic acidMerck MilliporeSigma (Sigma-Aldrich)Catalog #124737
ReagentTitansphere TiO, 5 μm, 500 mgGL ScienceCatalog #020-75000
ReagentSequencing Grade Modified TrypsinPromegaCatalog #V5113
ReagentPrimary Antibody anti-LRRK2 c41-2 AbcamCatalog #ab133474
ReagentIN04AOBIOUS IncCatalog #AOB13355
ReagentLactic acid solution, 85 %Merck MilliporeSigma (Sigma-Aldrich)Catalog #252476
ReagentAnti-LRRK2 (phospho S935) antibody [UDD2 10(12)]AbcamCatalog #ab133450
ReagentMLi-2Merck MilliporeSigma (Sigma-Aldrich)Catalog #SML3101
ReagentPolyethylenimine, Linear, MW 25000, Transfection GradePolysciences, Inc.Catalog #23966
ReagentHRP Anti-Rabbit IgGDianovaCatalog #AKC080
ReagentSep-Pak tC18 1 cc Vac Cartridge 50 mg Sorbent per CartridgeWatersCatalog #WAT054960
ReagentPierce™ Streptavidin Magnetic BeadsThermo FisherCatalog #88817
ReagentDMSOSupelcoCatalog #1.09678.0100
ReagentAnti-RAB10 (phospho T73) antibody [MJF-R21]AbcamCatalog #ab230261
ReagentOpti-MEM™ I Reduced Serum MediumThermo FisherCatalog #31985070
Troubleshooting
Safety warnings
Before performing the experiment, please optimize the incubation of biotin with TurboID-transfected cells to avoid overlabelling. This can be done by SDS-PAGE and Western blotting or mass spectrometry.

Please do not skip the detergent removal step as it is crucial for an optimal mass spectrometric analysis. Detergents like NP-40 will interfer with C18 nano-HPLC and lead to non-optimal resolution of peptides. Also, they can contaminate the mass spectrometers and cause ion suppression.

After performing the phosphopeptide enrichment, make sure that the exposition to basic pH is as short as possible because this can cause a loss of phosphorylations
Perform the enrichment shortly before measurement to keep native phosphorylation intact.
Before start
Please read the protocol carefully before you start the experiment to prepare all materials and methods and plan time and resources accordingly.
Cell culture
1d 2h 15m
HEK293T wt cells are cultured in 10 cm dishes in ReagentDulbeccos modified eagle medium (DMEM), high glucoseGibco - Thermo Fisher ScientificCatalog #41965062 with Concentration10 % (v/v) ReagentFetal bovine serum (FBS) SuperiorMerck MilliporeSigma (Sigma-Aldrich)Catalog #S0615 (hereafter "medium") at Temperature37 °C , 95 % and Concentration5 % (v/v) CO2 and passaged upon confluency.

For transient transfection and proximity labeling, cells were grown in 15 cm Petri dishes to 50-60 % confluency. For 1 replicate, 4x 15 cm dishes were used to have enough material for the interactome enrichment.
Transient transfection
Change medium and add Amount12.5 mL fresh medium to each plate.
For one replicate (4x 15cm dish), mixAmount7.5 µg of plasmid carrying TurboID-fusion construct with Amount5 mL ReagentOpti-MEM™ I Reduced Serum MediumThermo FisherCatalog #31985070 . Add Amount90 µL ReagentPolyethylenimine, Linear, MW 25000, Transfection GradePolysciences, Inc.Catalog #23966 (Concentration1 mg/mL stock solution).

Mix well by pipetting.
Incubate for Duration00:15:00 at TemperatureRoom temperature .

15m
Add Amount1.25 mL of the mix to each of the four plates. Tilt the plates and carefully add dropwise into medium on the side to not disturb adherent cells.

Incubate for Duration24:00:00 at Temperature37 °C , 95 % and Concentration5 % (v/v) CO2 .

1d
Addition of inhibitors
Change medium and add DMSO/inhibitors with this medium change
Add Amount5 µL of either Concentration10 millimolar (mM) ReagentMLi-2Merck MilliporeSigma (Sigma-Aldrich)Catalog #SML3101 , Concentration50 millimolar (mM) ReagentIN04AOBIOUS IncCatalog #AOB13355 (both in DMSO) or DMSO to Amount50 mL medium for Concentration1 micromolar (µM) final MLi-2 or Concentration5 micromolar (µM) final IN04 inhibitor concentration.

Add Amount12.5 mL of the prepared Amount50 mL mix to each of the four plates of 1 replicate.

Incubate for Duration01:00:00 at Temperature37 °C , 95 % and Concentration5 % (v/v) CO2

1h
TurboID proximity labelling
1h
Add Amount6.25 µL Concentration100 millimolar (mM) ReagentBiotinMerck MilliporeSigma (Sigma-Aldrich)Catalog #B4639 in DMSO carefully to each of the plates to start proximity labelling.

Incubate for Duration01:00:00 at Temperature37 °C , 95 % and Concentration5 % (v/v) CO2 .
1h
Harvest
20m
Adherent cells were washed carefully with 2x ReagentDulbeccos Phosphate-buffered salineGibco - Thermo Fisher ScientificCatalog #21300058 that was equilibrated to Temperature37 °C prior to washing.

Add Amount5 mL warm PBS with Concentration0.025 % (v/v) ReagentFormaldehyede 37% solutionCarl RothCatalog #7398 to each plate.

Toxic
Incubate for Duration00:10:00 at TemperatureRoom temperature .
10m
Remove liquid carefully
Add Amount5 mL warm Concentration50 millimolar (mM) Tris-HCl Ph7.4 to the adherent cells.

Incubate for Duration00:05:00 at TemperatureRoom temperature

5m
Remove liquid carefully.
Place cell dishes on ice and harvest cells with Amount10 mL ice-cold 1xReagentDulbeccos Phosphate-buffered salineGibco - Thermo Fisher ScientificCatalog #21300058 per plate.

Transfer ice-cold cell suspension to 50 mL Falcon tubes and pool the suspensions from 4x 15 cm dishes for each replicate (same transfection/inhibitor/biotin mix for each of the 15 cm dishes).
Wash cells twice with Amount10 mL ice-cold 1xReagentDulbeccos Phosphate-buffered salineGibco - Thermo Fisher ScientificCatalog #21300058 .
Pellet cells by centrifugation Centrifigation800 x g, 4°C for Duration00:05:00 in between.

Critical
Pellet cells by centrifugation Centrifigation800 x g, 4°C for Duration00:05:00 and snap freeze in liquid N2.

5m
Store cell pellets atTemperature-80 °C until further processing.
Pause
Cell lysis
35m
Place frozen cell pellets on ice. When working with cells and cell lysate please always work on ice until proteins are denatured or the protocol indicates to do otherwise.
Critical
Resuspend cell pellets in Amount16 mL lysis buffer (Concentration25 millimolar (mM) Tris-HCl Ph7.4 , Concentration150 millimolar (mM) NaCl, Concentration1 % (v/v) NP-40, Concentration5 millimolar (mM) MgCl2, Concentration1 millimolar (mM) Na3VO4, Concentration5 millimolar (mM) NaF, Concentration5 millimolar (mM) β-glycero phosphate, 1x ReagentcOmplete™, EDTA-free protease inhibitor cocktailRocheCatalog #11873580001 , Concentration1 millimolar (mM) DTT).

Incubate for Duration00:15:00 at Temperature4 °C while gently mixing/rolling.

15m
Pellet cell debris by centrifugation at Centrifigation16000 x g, 4°C for Duration00:20:00 .

20m
Take supernatant and continue with streptavidin enrichment. Discard the pellet.
Streptavidin enrichment
20h 3m
Equilibrate Amount0.5 mL ReagentPierce™ Streptavidin Magnetic BeadsThermo FisherCatalog #88817 (Amount5 mg per sample ) with 3x Amount500 µL lysis buffer in 1.5 mL tube using a magnetic rack.

3m
Add the equilibrated beads to the supernatant from Go to (see previous section).

Incubate for Duration20:00:00 at Temperature4 °C and gentle agitation to allow binding of biotinylated proteins to streptavidin beads.
20h
Overnight
Pellet beads by centrifugation Centrifigation2000 x g, 4°C for Duration00:15:00 .

Use a magnet to carefully decant "flow-through" of streptavidin beads without disturbing the bead pellet.
If necessary, repeat centrifugation to retain as many beads as possible.
Resuspend beads with Amount1 mL lysis buffer and transfer to a fresh 2 mL reaction tube.

Wash beads with Amount1 mL lysis buffer using a magnetic rack.

Repeat washing step.
On-bead digestion
22h
Equilibrate streptavidin beads twice with Amount1 mL Concentration50 millimolar (mM) ammonium bicarbonate to prepare samples for on-bead digestion.
Resuspend beads in Amount150 µL Concentration8 Molarity (M) urea.

Add TCEP ReagentTris(2-carboxyethyl)phosphin -hydrochloridMerck MilliporeSigma (Sigma-Aldrich)Catalog #C4706 for Concentration3 millimolar (mM) final concentration to reduce cysteines.

Incubate for Duration00:30:00 at Temperature37 °C and Shaker650 rpm .

Add IAA (ReagentIodoacetamideMerck MilliporeSigma (Sigma-Aldrich)Catalog #I1149-5G ) to Concentration6 millimolar (mM) final concentration to alkylate cysteines.

Toxic
Incubate for Duration00:30:00 at TemperatureRoom temperature and Shaker650 rpm in the dark.

30m
Dilute urea to Concentration4 Molarity (M) using Concentration50 millimolar (mM) ammonium bicarbonate.

Add Amount3 µg ReagentTrypsin/Lys-C Mix, Mass Spec Grade, 5 x 20ugPromegaCatalog #V5073 to sample.

Digestion
Incubate for Duration03:30:00 at Temperature37 °C and Shaker650 rpm .

3h 30m
Dilute urea concentration to Concentration1 Molarity (M) using Concentration50 millimolar (mM) ammonium bicarbonate.

Add Amount1.5 µg ReagentSequencing Grade Modified TrypsinPromegaCatalog #V5113 .

Digestion
Incubate for Duration18:00:00 at Temperature37 °C and Shaker650 rpm .

18h
Overnight
Remove residual detergents with the ReagentHiPPR™ Detergent Removal Spin Column KitThermo FisherCatalog #88305 (Amount200 µg per sample ) according to the manufacturer's instructions.

Critical
Acidify flow-through by adding formic acid to a final concentration of Concentration2 % (v/v) .

After mixing, check if Ph2 or lower. This is important since acidic pH stops trypsin digestion and is crucial for a successful C18 desalting.

Critical
Add Concentration1 % (v/v) acetonitrile (ACN) final concentration and desalt your sample using ReagentSep-Pak tC18 1 cc Vac Cartridge 50 mg Sorbent per CartridgeWatersCatalog #WAT054960 and a vacuum manifold.

Wet cartridges with Amount1 mL pure ACN.

Equilibrate cartridges with Amount2 mL Concentration1 % (v/v) ACN, Concentration0.1 % (v/v) formic acid.

Add sample and apply it slowly to the C18 resin. Don't open the valve fully to apply slowly.
Wash peptides with Amount2 mL Concentration1 % (v/v) ACN, Concentration0.1 % (v/v) formic acid.

Elute peptides into low-binding 1.5 mL tube with Amount1 mL Concentration50 % (v/v) ACN, Concentration0.1 % (v/v) formic acid.

For further analysis, split sample for peptide and phosphopeptide analysis. Therefore, use 10 % of sample for "normal" peptide analysis (Fraction 1), and 90 % of sample for subsequent phosphopeptide enrichment and phosphopeptide analysis (Fraction 2).

Dry both fractions in a
Equipment
Concentrator Plus
NAME
Centrifugal vacuum concentrator
TYPE
Eppendorf
BRAND
5305000568
SKU
LINK
.
Pause
For Fraction 1, continue directly to "Mass spectrometric analysis".
For Fraction 2, continue with "Phosphopeptide enrichment".
Phosphopeptide enrichment
1h 2m
Weigh Amount0.5 mg beads per sample (if Amount50 µg peptides) ReagentTitansphere TiO, 5 μm, 500 mgGL ScienceCatalog #020-75000 and resuspend in Loading buffer 1 (Concentration0.1 Molarity (M) ReagentGlycolic acidMerck MilliporeSigma (Sigma-Aldrich)Catalog #124737 , Concentration70 % (v/v) ACN, Concentration5 % (v/v) trifluoroacetic acid (TFA)) so that Amount10 µL per 1 mg beads .

To minimize unspecific binding, incubate TiO2 beads in Loading buffer 1 for Duration00:20:00 at TemperatureRoom temperature and Shaker1200 rpm prior to peptide incubation

20m
Resuspend approx. Amount50 µg of dried peptides in Amount200 µL Loading buffer 1.

Incubate for Duration00:10:00 at Temperature37 °C for proper resuspension.

10m
Add equilibrated beads to peptides at a peptide:bead ratio of 1:10. If prepared as described, add Amount5 µL per sample.

Incubate for Duration00:20:00 at TemperatureRoom temperature in rolling incubator.

20m
Prepare self-made, single-layered C8 Stage tips. See
Citation
Rappsilber J, Mann M, Ishihama Y (2006). Protocol for micro-purification, enrichment, pre-fractionation and storage of peptides for proteomics using StageTips.
LINK
for details.
Use Reagent3M™ Empore™ C18 47 mm Extraction Disc Model 2215 20 pack 3 packs per case3M corporationCatalog #2215 to make the tips.

Equilibrate C8 Stage tips with Loading buffer 1.
Settle incubated TiO2 beads by centrifugation Centrifigation10000 x g for Duration00:02:00 .

2m
Transfer Amount150 µL of supernatant to fresh low-binding tube and keep for second enrichment step, see Go to .

Use residual supernatant to transfer beads to equilibrated C8 Stage tips.
Centrifuge for Duration00:02:00 at Centrifigation500 x g and add flow-through to supernatant fraction from step Go to .

2m
Wash beads that were retained by C8 Stage tips with Amount50 µL Wash buffer 1 (Concentration80 % (v/v) ACN, Concentration1 % (v/v) TFA) and centrifuge at Centrifigation500 x g for Duration00:02:00 .

2m
Wash beads with Amount50 µL Wash buffer 2 (Concentration10 % (v/v) ACN, Concentration0.2 % (v/v) TFA) and centrifuge at Centrifigation500 x g for Duration00:02:00 . Transfer tips to new vial.

2m
Prepare low-binding tubes with Amount60 µL Concentration10 % (v/v) formic acid for phosphopeptide elutions to directly acidify them and minimize loss of phosphorlyation by ammonium hydroxide.

Elute bound phosphopeptides with Amount30 µL Elution buffer 1 (Concentration1 % (v/v) NH4OH) by centrifugation at Centrifigation500 x g for Duration00:02:00 and directly transfer elution to prepared tubes (Go to ).

2m
Elute residual bound phosphopeptides with Amount30 µL Elution buffer 2 (Concentration5 % (v/v) NH4OH, Concentration25 % (v/v) ACN) by centrifugation at Centrifigation500 x g for Duration00:02:00 and directly transfer elution to prepared tubes (Go to ).

2m
Repeat phosphopeptide protocol with retained supernatant from Go to and repeat protocol with Loading buffer 2 (Concentration20 % (v/v) ReagentLactic acid solution, 85 %Merck MilliporeSigma (Sigma-Aldrich)Catalog #252476 , Concentration70 % (v/v) ACN, Concentration5 % (v/v) TFA) instead of Loading buffer 1.

This second enrichment step maximizes yield of phosphopeptide by repeating the enrichment and changing the specificity by using lactic acid instead of glycolic acid.
Combine phosphopeptide elutions and dry them by vaccuum evaporation.
Pause
Mass spectrometric analysis
6h 8m
Resuspend samples in mass spectrometric (MS) buffer (Concentration3 % (v/v) ACN, Concentration0.1 % (v/v) formic acid), measure peptide concentration by Nanodrop and adjust concentration to Concentration0.25 µg/µL if possible.

Load Amount500 ng peptides onto a Thikness50 cm ReagentAcclaim™ PepMap™ 100 C18 HPLC ColumnsThermo ScientificCatalog #164945 connected to an EASY-nLC 1200 nano-LC system coupled to a QExactive HF mass spectrometer.

For normal peptides (Fraction 1), resolve peptides across a Duration03:38:00 active gradient at a 150 nL/min flow rate.
For phosphopeptides (Fraction 2), resolve peptides across a Duration02:30:00 min active gradient at a 150 nL/min flow rate.

6h 8m
Perform mass spectrometric analysis in data-independent acquisition mode with 24 (Fraction 1) or 20 (Fraction 2) variable windows with 1 m/z overlaps.

Record full mass spectra in the Orbitrap at a resolution of 120K in the range of 300-1650 m/z (Fraction 1) or 350-1600 m/z (Fraction 2) with a maximum injection time of 60 ms and an AGC target of 3e6.
Isolate precursor ions in the quadrupole and fragment them with stepped HCD at 28 ±3 % NCE (normalized collision energy).
Record fragment mass spectra in the Orbitrap at a resolution of 30K, an AGC target of 1e6 and maximum injection time set to auto.
Data analysis
Analyze raw data with Spectronaut in directDIA mode.
For Fraction 1, normal peptides, use default BGS settings except for minimal peptide lengths 6.
For Fraction 2, phosphopeptides, change default BGS settings to also include variable modifications phosphorylation at S, T, and Y, deamidation at N and Q as well as glutamine to pyro-glutamine modification. Set the Normalization Type Filter to include phosphorylated residues. Enable the PTM workflow and set the PTM localization filter to 0.75.
Use Swissprot database containing protein sequences from homo sapiens and additionally, a contaminant database like this one:
Citation
Frankenfield AM, Ni J, Ahmed M, Hao L (2022). Protein Contaminants Matter: Building Universal Protein Contaminant Libraries for DDA and DIA Proteomics.
LINK

Retain only proteins or peptides that were confidently identified with a Q-value ≤ 0.01.
Export quantification results as pivot report for statistical analysis and hypothesis testing.
Use an appropriate tool for statistical analysis. For example, you can use Perseus.
Citation
Tyanova S, Cox J (2017). Perseus: A Bioinformatics Platform for Integrative Analysis of Proteomics Data in Cancer Research.
LINK

For statistical analysis of Fraction 1:
Load data from Spectronaut into your tool.
Filter out Contaminants
Log2 transform quantities.
Group all replicates of one condition so you can use these groups for subsequent filtering and analysis.
Filter out proteins that have been identified and quantified inconsistently in less than 3 or 4 of 4 biological replicates across all conditions, i.e. if a protein has been identified sparsely in all conditions, filter it out, but if it is identified in 3 or 4 of 4 replicates in one condition or more, keep it.
Filter out proteins that have been identified and quantified based on only 1 precursor.
Impute missing values using a tail-based imputation. This step is crucial to perform hypothesis tests.
Use two-sample t-tests to determine significant differences between two conditions and multiple sample t-tests (ANOVA-based) to determine significant differences between more than 2 conditions.
Filter results for significantly changed proteins
You can also perform a post-hoc Tukey test based on the results from the ANOVA to determine between which conditions significant differences were identified. Then, use these results to filter out hits that are enriched in the control or filter hits that are significantly changed between certain conditions.
Normalize values to z-scores and average replicates of the same condition.
Perform hierarchical cluster analysis to identify and visualize cluster of protein that behave similarly and are enriched or depleted for one or more conditions.
Use clusters from previous step to perform further interactome analysis.
For statistical analysis of Fraction 2
Use the phosR package to process phosphosites.

Citation
Kim HJ, Kim T, Hoffman NJ, Xiao D, James DE, Humphrey SJ, Yang P (2021). PhosR enables processing and functional analysis of phosphoproteomic data.
LINK

Keep only phosphosites that were identified in more than 2 of 4 replicates for at least one condition.
Impute missing values first using a site- and condition specific imputation, and then a paired-tail imputation and normalize resulting values.
Export data from phosR and continue in your statistical tool of choice or continue in R.
Perform hypothesis tests for phosphosites as described for proteins above.
Protocol references
Tyanova, S. et al. (2016) ‘The Perseus computational platform for comprehensive analysis of (prote)omics data’, Nature Methods. Nature Publishing Group, pp. 731–740. Available at: https://doi.org/10.1038/nmeth.3901.

Kim, H.J. et al. (2021) ‘PhosR enables processing and functional analysis of phosphoproteomic data’, Cell Reports, 34(8), p. 108771. Available at: https://doi.org/10.1016/J.CELREP.2021.108771.

Bruderer, R. et al. (2017) ‘Optimization of Experimental Parameters in Data-Independent Mass Spectrometry Significantly Increases Depth and Reproducibility of Results’, Molecular & Cellular Proteomics, 16(12), p. 2296. Available at: https://doi.org/10.1074/MCP.RA117.000314.

Utriainen, M. and Morris, J.H. (2023) ‘clusterMaker2: a major update to clusterMaker, a multi-algorithm clustering app for Cytoscape’, BMC Bioinformatics, 24(1), pp. 1–28. Available at: https://doi.org/10.1186/S12859-023-05225-Z/FIGURES/10.
Citations
Step 51
Tyanova S, Cox J. Perseus: A Bioinformatics Platform for Integrative Analysis of Proteomics Data in Cancer Research.
https://doi.org/10.1007/978-1-4939-7493-1_7
Step 53.1
Kim HJ, Kim T, Hoffman NJ, Xiao D, James DE, Humphrey SJ, Yang P. PhosR enables processing and functional analysis of phosphoproteomic data.
https://doi.org/10.1016/j.celrep.2021.108771
Acknowledgements
This research was funded by Aligning Science Across Parkinson’s (grant ASAP-000519 to S.R.P., S.K. and F.S) through the Michael J. Fox Foundation for Parkinson’s Research (MJFF). This work was also supported by funding of the German Research Foundation (DFG, F.S.: 496470458 and 516836828). We thank the laboratory of Samara Reck-Peterson for providing us with the initial protocol for BioID on which parts of this protocol are based.