Project description:The development of mirror-image biology systems and related applications is hindered by the lack of effective methods to sequence mirror-image (D-) proteins. Although natural-chirality (L-) proteins can be sequenced by bottom–up liquid chromatography–tandem mass spectrometry (LC–MS/MS), the sequencing of long D-peptides and D-proteins with the same strategy requires digestion by a site-specific D-protease before mass analysis. Here we apply solid-phase peptide synthesis and native chemical ligation to chemically synthesize a mirror-image version of trypsin, a widely used protease for site-specific protein digestion. Using mirror-image trypsin digestion and LC–MS/MS, we sequence a mirror-image large subunit ribosomal protein (L25) and a mirror-image Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4), and distinguish between different mutants of D-Dpo4. We also perform writing and reading of digital information in a long D-peptide of 50 amino acids. Thus, mirror-image trypsin digestion in conjunction with LC–MS/MS may facilitate practical applications of D-peptides and D-proteins as potential therapeutic and informational tools.
Project description:In the process of cell culture in vitro, we usually find that the cells show signs of aging, which is that the passed cells are unable to stick to the wall. Experience tells us that the time it takes for trypsin to digest the adherent cells is important. If the digestion time is too short, enough cells cannot be obtained for passage, while if the digestion time is too long, a large number of senescent cells will also be digested. The substances released by the death and decomposition of these senescent cells will affect the function of those active cells, resulting in the failure of the recovery of the whole daughter cell line. This project starts from the question of the global difference among cells undergoing the multiple rounds of mitosis in one culture dish. RNA sequencing was conducted to investigate the transcriptome signatures of cells with different sensitivity response to trypsin.
Project description:High specificity and ease of use make trypsin the most used enzyme in proteomics. Proteases with complementary cleavage specificity to trypsin have been applied to obtain additional data. However, use of proteases with broad specificity proved especially challenging. In this work, we analyzed the characteristics of five protease alternatives to trypsin for protein identification and sequence coverage when applied to S. pombe whole cell lysates. The specificity of the protease heavily impacted on the number of proteins identified. Proteases with higher specificity let to the identification of more proteins than proteases with lower specificity. However, AspN, GluC, chymotrypsin and proteinase K largely benefited from being paired with trypsin in sequential digestion, as had been shown by us for elastase before. In the most extreme case, the addition of trypsin to a proteinase K digest increased the number of identified proteins by 524 %. Also, AspN (82 %) and GluC (74 %) protein identifications largely improved following the additional digestion with trypsin. In general, protein identifications improved most over the use of the single protease when the enzymes followed on an initial digestion with trypsin. In the most extreme case, the sequential digest with trypsin and AspN yielded even higher number of protein identifications than digesting with trypsin alone.
Project description:Cross-linking/mass spectrometry has become an important approach for studying protein structures and protein-protein interactions. The amino acid composition of some protein regions impedes the detection of cross-linked residues, although it would yield invaluable information for protein modelling. Here, we report on a sequential digestion strategy with trypsin and elastase to penetrate regions with a low density of trypsin cleavage sites. We exploited intrinsic substrate recognition proper-ties of elastase to specifically target larger tryptic peptides. Our application of this protocol to the TAF4-12 complex allowed us to identify cross-links in previously inaccessible regions.
Project description:Immunoprecipitation-mass spectrometry (IP-MS) has become the method of choice for discovering protein-protein interaction (PPI) under native conditions. The success of the IP-MS depends on the efficiency of trypsin digestion and recovery of the tryptic peptides for MS analysis. Several different protocols have been used for trypsin digestion of protein complexes in IP-MS studies, but no systematic studies have been conducted on the impact of trypsin digestion conditions on the identification of PPI. Here, we identified the interactome of transcription factor p65 (RelA) to test five distinct trypsin digestion methods (two using “on-bead”, two using “in-solution”, and one using “in-gel” protocols) and determined which method yielded the best interactome coverage. Our study indicates that high-abundance RelA interactors can be universally identified by all five methods, but the identification of low-abundance RelA interactors is significantly affected by the choice of trypsin digestion methods. We found that eluting RelA complex with sodium dodecyl sulfate (SDS) and followed by filter-aided sample preparation (FASP)/in-solution digestion is the best among the methods that were tested. We also found that different digestion protocols influences the selected reaction monitoring (SRM)-MS quantification of PPIs, suggesting that optimization of trypsin digestion condition may be required for robust study of targeted analysis of PPIs.