Mesoporous Materials in Peptidome Analysis

Abstract

Biologically active peptides, such as peptide hormones and cytokines, play pivotal roles in human health and disease development, as these peptides are important regulators for diverse functions, which range from the endocrine to the inflammatory and the nervous systems. Endogenous peptides can result from the proteolytic cleavage of proteins, and are indicative of protease activity, degradation, and degeneration. The overall concentrations of peptides in biological samples reflect certain biological events and may provide useful information for clinical diagnosis. Therefore, the comprehensive analysis of peptides in complex biological mixtures, termed peptidomics, can contribute to a better understanding of the biochemical functions of endogenous peptides, as well as to the development of diagnostic and prognostic biomarkers. To profile the peptidome in complicated samples, such as human serum, typical procedures involve sample collection, extraction, separation, detection, and data mining (Scheme 1). Of the five key steps, the selective extraction of peptides has been identified as an important obstacle to overcome for progress in peptidome research, because of the complexity and high dynamic range of biomolecules present in the samples from which the peptides must be extracted. For example, the detection of low-abundance peptides in human serum is very challenging because they are overwhelmed by larger and more abundant proteins, salts, and lipids. To confront this challenge, Zou s group has recently developed a highly efficient and selective method to extract peptides from human serum by using ordered mesoporous carbon (OMC). The 4.8 nm pore size of the OMC material enables a molecular-weight cut-off of approximately 10 kDa, which is sufficient to remove the majority of larger interfering serum proteins. The use of OMC greatly enhances the overall extraction efficiency of peptides, which includes peptides in the low mass range (< 2 kDa) that are traditionally difficult to extract. When combined with twodimensional liquid chromatography and tandem mass spectrometry (2D LC-MS/MS), the researchers were able to identify 3402 unique endogenous peptides from 20 mL of serum. The significantly greater number of serum peptides identified by using this technique demonstrates the advantageous efficiency of mesoporous-based extraction over other sample treatment techniques. Mesoporous materials, such as OMC, have the desirable properties of an ideal extraction material, which include a high surface area, large pore volume, chemical inertness, and good mechanical stability. In recent years, various mesoporous materials have been synthesized to possess a welldefined pore-size distribution and controllable surface functionality. The narrow size distribution of the ordered mesopores facilitates size-selective extraction of endogenous peptides and size exclusion of larger proteins. For example, the highly ordered mesoporous-silica particles in MCM-41, have a pore size of 2 nm and a molecular-weight cut-off of Scheme 1. Typical steps involved in profiling peptidomes from complicated samples. The use of new mesoporous materials improves the efficiency and selectivity of peptide extraction.