Miniaturized on-line digestion system for the sequential identification and characterization of protein analytes

A flow-through nanoporous alumina trypsin bioreactor for mass spectrometry peptide fingerprinting

Mass spectrometry-based proteomics benefits from efficient digestion of protein samples. In this study, trypsin was immobilized on nanoporous anodized alumina membranes to create an enzyme reactor suitable for peptide mass fingerprinting. The membranes were derivatized with 3-aminopropyltriethoxysilane and the amino groups were activated with carbonyldiimidazole to allow coupling of porcine trypsin via ε-amino groups. The function was assessed using the artificial substrate Nα-Benzoyl-L-arginine 4-nitroanilide hydrochloride, bovine ribonuclease A and a human plasma sample. A 10-membrane flow-through reactor was used for fragmentation and MS analysis after a single pass of substrate both by collection of product and subsequent off-line analysis, and by coupling on-line to the instrument. The peptide pattern allowed correct identification of the single target protein in both cases, and of >70 plasma proteins in single pass mode followed by LC-MS analysis. The reactor retained 76% of the initial activity after 14days of storage and repeated use at room temperature.

SIGNIFICANCE

This manuscript describes the design of a stable enzyme reactor that allows efficient and fast digestion with negligible leakage of enzyme and enzyme fragments. The high stability facilitates the use in an online-setup with MS detection since it allows the processing of multiple samples within an extended period of time without replacement.

Protein identification using nano-HPLC-MS: ESI-MS and MALDI-MS interfaces

Body fluids and body tissues have a myriad of peptides and proteins that, very often, the traditional methodologies of proteomics, such as conventional gel electrophoresis or mass spectrometry, are unable to characterize. We describe two protocols to characterize high molecular weight peptides (>3 kDa) and intact proteins involving on-line trypsin digestion, separation of the digests by nano-HPLC, and analysis by mass spectrometry using two different ionization sources (matrix-assisted laser desorption and electrospray ionization). These protocols have the advantage of promoting protein denaturation in an aqueous-organic solvent, which reduces the derivatization of the sample and facilitates an in-depth analysis for detection and identification of proteins. Additional advantages include the following: (1) integration of these protocols into standard proteomic workflows after the preprocessing of samples and separation; (2) use of high-resolution monolithic columns; and (3) the ability to acquire information from minimal amounts of sample.

Nanoelectrospray emitters: trends and perspective

The benefits of electrospray ionization are many, including sensitivity, robustness, simplicity and the ability to couple continuous flow methods with mass spectrometry. The technique has seen further improvement by lowering flow rates to the nanoelectrospray regime (<1,000 nL/min), where sample consumption is minimized and sensitivity increases. The move to nanoelectrospray has required a shift in the design of the electrospray source which has mostly involved the emitter itself. The emitter has seen an evolution in architecture as the shape and geometry of the device have proved pivotal in the formation of sufficiently small droplets for sensitive MS detection at these flow rates. There is a clear movement toward the development of emitters that produce multiple Taylor cones. Such multielectrospray emitters have been shown to provide enhanced sensitivity and sample utilization. This article reviews the development of nanoelectrospray emitters, including factors such as geometry and the manner of applying voltage. Designs for emitters that take advantage of multielectrospray are emphasized.

A Mass Spectrometric Investigation of Native and Oxidatively Inactivated Chloroperoxidase

The enzyme chloroperoxidase (CPO) found in Caldariomyces fumago is able to catalyze several stereoselective oxidation reactions by using a clean oxidant, usually hydrogen peroxide (H(2)O(2)), without the need for expensive cofactor generation. CPO's lack of operational stability, however, is a major limitation for its commercial use. In the present study, a capillary-LC on-line trypsin-digestion system combined with reversed-phase chromatography and mass spectrometric detection was optimized for studying the primary sequence of CPO. Samples containing native CPO, CPO treated with H(2)O(2), and CPO oxidatively inactivated by the use of indole and H(2)O(2) were analyzed and compared. Three oxidized peptides were found in the samples treated with H(2)O(2). Two additional oxidized peptides were found in the CPO samples that were completely inactivated, one of which contained an oxidized cysteine residue, Cys50, which is an essential amino acid due to its function as the axial ligand to the iron in the heme--the prosthetic group in CPO. In addition, the heme group was absent in the inactivated samples but was readily detected in other samples.