Characterization of protein expression and folding in cell-free systems by maldi-tof mass spectrometry

Mechanistic study of laser desorption/ionization of small molecules on graphene oxide multilayer films

Graphene and graphene oxide (GO) films have been explored to develop an efficient laser desorption/ionization mass spectrometry (LDI-MS) platform for the analysis of chemically and biologically important small molecules. The GO films were prepared by layer-by-layer (LBL) assembly cycles (one to ten layers) with precisely controlled thickness and surface roughness which are important structural factors for laser energy absorption capacity and laser energy transfer for efficient LDI-MS analysis. Amino acids, saccharides, and pyrenylated molecules were analyzed by LDI-MS on the LBL assembled GO films to reveal their structural influence on LDI-MS analysis of small molecules. Then, the structural influence of LBL assembled GO films on synergistic effect was investigated to develop an efficient and widely applicable LDI-MS analysis platform with an additional multiwalled carbon nanotube (MWCNT) layer. We found that the optimum number of GO film layers for LDI-MS analysis was dependent on the chemical structures of small molecules, and the laser energy threshold needed for LDI of small molecules on GO/MWCNT films could be lowered as the number of LBL assembled GO films increased underneath the MWCNT layer.

Fabrication of alternating multilayer films of graphene oxide and carbon nanotube and its application in mechanistic study of laser desorption/ionization of small molecules

Graphene, graphene oxide (GO), and multi-walled carbon nanotube (MWCNT) have been actively explored as matrix for laser desorption/ionization mass spectrometry (LDI-MS) in place of conventional organic matrix. Recently, the GO/MWCNT double layer films on a solid substrate showed excellent applicability in small molecule analysis, enzyme activity assay and tissue imaging. In the present study, LDI processes of small molecules on multilayers of alternating MWCNT and GO hybrid films were thoroughly investigated. We found that the LDI efficiency of small molecules was affected by thickness, assembly sequence and surface roughness of the hybrid films that were controlled by varying the number of layer-by-layer (LBL) assembly cycles. The study would provide useful basic information to develop an efficient LDI-MS platform based on carbon nanomaterials.

Cell-free synthesis and folding of transmembrane OmpA reveals higher order structures and premature truncations

We use a cell-free transcription-translation system to monitor the effect of different lipids on the synthesis and folding of the transmembrane domain of the outer membrane protein OmpA from E. coli under physiological conditions. Folding is consistent with previous observations made in vitro at high pH. Synthesis and folding yields are optimal in phosphocholine lipids, particularly in short chain lipids and small vesicles, while lipid rafts do not promote folding compared to the folding in the absence of lipids. Truncated species are observed during translation in the presence of the periplasmic chaperone Skp, which likely binds to the newly synthesized polypeptide chain during cell-free translation and thus prematurely terminate polypeptide chain synthesis. In contrast, folded and unfolded dimers of OmpA correlate negatively with folding yields. This suggests that dimer formation competes with folding and insertion of monomeric OmpA, though folded dimers slowly appear to convert to folded monomers.

Cell-free protein synthesis energized by slowly-metabolized maltodextrin

BACKGROUND

Cell-free protein synthesis (CFPS) is a rapid and high throughput technology for obtaining proteins from their genes. The primary energy source ATP is regenerated from the secondary energy source through substrate phosphorylation in CFPS.

RESULTS

Distinct from common secondary energy sources (e.g., phosphoenolpyruvate - PEP, glucose-6-phosphate), maltodextrin was used for energizing CFPS through substrate phosphorylation and the glycolytic pathway because (i) maltodextrin can be slowly catabolized by maltodextrin phosphorylase for continuous ATP regeneration, (ii) maltodextrin phosphorylation can recycle one phosphate per reaction for glucose-1-phosphate generation, and (iii) the maltodextrin chain-shortening reaction can produce one ATP per glucose equivalent more than glucose can. Three model proteins, esterase 2 from Alicyclobacillus acidocaldarius, green fluorescent protein, and xylose reductase from Neurospora crassa were synthesized for demonstration.

CONCLUSION

Slowly-metabolized maltodextrin as a low-cost secondary energy compound for CFPS produced higher levels of proteins than PEP, glucose, and glucose-6-phospahte. The enhancement of protein synthesis was largely attributed to better-controlled phosphate levels (recycling of inorganic phosphate) and a more homeostatic reaction environment.

Folding and assembly of large macromolecular complexes monitored by hydrogen-deuterium exchange and mass spectrometry

Recent advances in protein mass spectrometry (MS) have enabled determinations of hydrogen deuterium exchange (HDX) in large macromolecular complexes. HDX-MS became a valuable tool to follow protein folding, assembly and aggregation. The methodology has a wide range of applications in biotechnology ranging from quality control for over-expressed proteins and their complexes to screening of potential ligands and inhibitors. This review provides an introduction to protein folding and assembly followed by the principles of HDX and MS detection, and concludes with selected examples of applications that might be of interest to the biotechnology community.

Enhanced cell-free protein expression by fusion with immunoglobulin Ckappa domain

While cell-free systems are increasingly used for protein expression in structural and functional studies, several proteins are difficult to express or expressed only at low levels in cell-free lysates. Here, we report that fusion of the human immunoglobulin kappa light chain constant domain (Ckappa) at the C terminus of four representative proteins dramatically improved their production in the Escherichia coli S30 system, suggesting that enhancement of cell-free protein expression by Ckappa fusion will be widely applicable.

Current literature in mass spectrometry

In order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (6 Weeks journals ‐ Search completed at 4th. Oct. 2006)