Quantifying raft proteins in neonatal mouse brain by 'tube-gel' protein digestion label-free shotgun proteomics

Hongwei Yu^*¹ , Bassam Wakim^*² , Man Li¹^,6 , Brian Halligan³ , G Stephen Tint⁴ and Shailendra B Patel¹^,5

¹Division of Endocrinology, Metabolism and Nutrition, Medical College of Wisconsin, Milwaukee, WI 53226, USA

²Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA

³National Center for Proteomics Research, Biotechnology and Bioinformatics Center, Medical College of Wisconsin, Milwaukee, WI 53226, USA

⁴Research Service, Department of Veterans Affairs New Jersey Health Care System, East Orange, NJ 07018, USA, and Department of Medicine, UMDNJ-New Jersey Medical School, Newark, NJ 07103-2714, USA

⁵Department of Veterans Affairs, Clement J. Zablocki Medical Center, Milwaukee, WI 53295, USA

⁶Qilu Hospital, Shandong University, 44 West Wenhua Road, Jinan, 250012, P. R. China

author email corresponding author email* Contributed equally

Proteome Science 2007, 5:17doi:10.1186/1477-5956-5-17


Published:	24 September 2007

Abstract

Background

The low concentration and highly hydrophobic nature of proteins in lipid raft samples present significant challenges for the sensitive and accurate proteomic analyses of lipid raft proteins. Elimination of highly enriched lipids and interfering substances from raft samples is generally required before mass spectrometric analyses can be performed, but these procedures often lead to excessive protein loss and increased sample variability. For accurate analyses of the raft proteome, simplified protocols are needed to avoid excessive sample handling and purification steps.

Results

We have devised a simple protocol using a 'tube-gel' protein digestion that, when combined with mass spectrometry, can be used to obtain comprehensive and reproducible identification and quantitation of the lipid raft proteome prepared from neonatal mouse brain. Lipid rafts (detergent-resistant membranes using Triton X-100 extraction) prepared from neonatal mouse brain were directly incorporated into a polyacrylamide tube-gel matrix without prior protein separation. After in-gel digestion of proteins, nanospray LC-MS/MS was used to analyze the extracted peptides, and the resulting spectra were searched to identify the proteins present in the sample. Using the standard 'label-free' proteomics approach, the total number of MS/MS spectra for the identified proteins was used to provide a measure of relative protein abundances. This approach was successfully applied to lipid rafts prepared from neonatal mouse brain. A total of 216 proteins were identified: 127 proteins (58.8%) were predicted to be membrane proteins, or membrane-associated proteins and 175 proteins (~80%) showed less than a 2-fold variation in the relative abundance in replicate samples.

Conclusion

The tube-gel protein digestion protocol coupled with nanospray LC-MS/MS (TubeGeLC-MS/MS) offers a simple and reproducible method for identifying and quantifying the changes of relative abundances in lipid raft proteins from neonatal mouse brain and could become a useful approach for studying lipid raft proteins from various tissues.