The transferred energy from a fluorescent donor is converted into molecular vibrations if the acceptor is a non-fluorescent dye (quencher). When the FRET is terminated (by separating donor and acceptor), an increase of donor fluorescence can be detected. The design and synthesis work at CPC for FRET and TR-FRET peptide substrates include modification of sequences, selection of donor/quencher pairs, improvement of FRET substrate solubility and quenching efficiency.
Genomics research shows that more than a million proteins are encoded by approximately 30,000 human genes. Proteomics, the study of proteins encoded by the genome, includes identifying post-translational modifications, structural analyses, protein localization studies, and protein quantitation. Mass spectroscopybased techniques have evolved as a powerful tool in proteomics. Stable isotope-labeled peptides (SIL peptides) are chemically and physically indistinguishable from their endogenous counterparts concerning retention time, ionization efficiency, and fragmentation pathways.
Peptides play a vital role in the pharmaceutical industry and drug therapeutic development; however, their in vivo applications are sometimes limited due to fast degradation by proteases, poor solubility, antigenic responses, and glomerular filtration in the kidney. The covalent attachment of polyethylene glycol (PEG) chains to peptides is one approach that can reduce immunogenicity, improve solubility, and reduce renal clearance.
Hydrocarbon-stapled peptides are locked into their bioactive alpha-helical conformation through the site-specific introduction of a chemical brace, an all-hydrocarbon staple. The idea of peptide stapling was introduced to overcome the limitations of two broad classes of therapeutic agents (small molecules and protein biologics) in targeting intracellular protein-protein interactions. Small molecules only work on proteins with a specific surface feature, and most protein biologics do not penetrate cells. Because stapled peptides are locked into a stabilized α-helical structure (the most common element of protein secondary structures), they can easily penetrate cells.
Axiak-Bechtel, Sandra M., Stacey B. Leach, David G. Scholten, Jessica R. Newton-Northup, Brendan J. Johnson, H. E. Durham, Kenneth A. Gruber, and Michael F. Callahan. Pharmacology Research & Perspectives 9, no. 3 (2021): e00777.
TCMCB07 [a cyclic substituted melanocortin antagonist with the structure Ac- Nle- cyclo[Asp- Pro- DNal(2’)-Arg- Trp- Lys]- DVal- DPro- NH2] was manufactured by CPC Scientific Inc. under cGMP conditions. Active pharmaceutical ingredient was dissolved in milliQ water at 10 mg ml−1, sterile filtered [..]”
Paul S. Marinec, Kyle E. Landgraf, Maruti Uppalapati, Gang Chen, Daniel Xie,‡ Qiyang Jiang, Yanlong Zhao, Annalise Petriello, Kurt Deshayes, Stephen B. H. Kent, Dana Ault-Riche*, and Sachdev S. Sidhu* ACS Chem. Biol. 2021, 16, 3, 548–556.
- Chinese Peptide Company, Hangzhou Economic and Technical Development Zone, China, 310018.
"The D-VEGF-A polypeptide chain (COOH acid, residues 8-109 (1)) was chemically synthesized using solid phase peptide synthesis (SPPS) and native chemical ligation, and folded to form the protein covalent homodimer, using methods adapted from our previous work [..]"
Protein-protein and protein-peptide interactions play critical roles in all types of cellular processing. Peptides are natural partners to proteins and, as ligands, bind to proteins with high affinity due to their capacity to adapt to the often flexible protein surface. Despite this, peptides have drawbacks as drug candidates that include low plasma bioavailability, instability from proteolytic enzymes, and poor passive membrane permeability. Some success has been achieved with linear peptides, particularly peptides that maintain α-helical secondary structures. These motifs can be introduced to stabilized α-helical motifs by common “peptide-stapling” approaches, but stapled peptides can suffer from low bioactivity and poor solubility. Another strategy to maintain peptide secondary structure is modification by macrocyclization.
Curreli, Francesca, Sofia MB Victor, Shahad Ahmed, Aleksandra Drelich, Xiaohe Tong, Chien-Te K. Tseng, Christopher D. Hillyer, and Asim K. Debnath. Mbio 11, no. 6 (2020): e02451-20.
We have synthesized (CPC Scientific, Inc.) four stapled peptides, as depicted in Figure 2. We also synthesized the linear peptide, NYBSP-C, as a control. Besides, we purchased a linear peptide, SBP1, to use as a control, which was reported recently to bind to SARS-CoV-2 RBD with high affinity (KD = 47nM).
Mutations to the RBD of SARS-CoV have resulted in the reorganization of SARS-CoV-2 RBD, specifically to the loops that are in close proximity to the ACE2-binding ridge. Due to these structural changes, an additional intramolecular main-chain hydrogen bond is gained between Asn487 and Ala475 (Figure 4a). The Asn487–Ala475 hydrogen bond causes the RBM of SARS-CoV-2 to be more structurally compact, enabling the loop containing Ala475 to move into closer proximity to the ACE2 α1 helix. Closer contact between the RBM and α1 helix of ACE2 results in more intermolecular interactions (Figure 4a,b). Some of these interactions include hydrogen bonds between Gln493 (SARS-CoV-2) and Glu35 (ACE2),[3b,c] and main-chain hydrogen bonds between Gly502 and Lys31.
This guide will help you understand how to read ESI spectra for large and complex bio-molecules like peptides. Other techniques such as high-performance liquid chromatography (HPLC) show one major peak (i.e., absorbance and purity for RP-HPLC) in the spectra, making the interpretation straightforward. ESI-MS spectra are more complicated due to the multiplicity of the data. While most small molecules (100-500 AMU) behave well in ESI-MS and ionize as a single charged state, larger biomolecules, such as peptides, ionize as multiple charged variants. A major advantage of ESI-MS over other mass spectroscopy techniques is that molecular fragmentation is rare (t-Boc groups and a few other protection groups are an exception), which is why ESI-MS is often referred to as a soft ionization technique.
