Stable isotope labeled proteins and peptides are necessary for NMR studies. Preparation of these samples is time-consuming and labor-intensive work. Sometimes it is difficult to be realized in a regular biochemical laboratory, especially in the case of site-specific labeling, fragment labeling, and partial labeled isotopes. Creative Biostructure provides isotope labeled protein or peptide production services for NMR studies in the characterization of macromolecules at high atomic resolution.
Isotopic enrichment is an integral part of the advancements made by NMR. Four isotopes, 1H, 15N, 13C, and 2H are commonly used in biomolecular NMR. Among these isotopes, only 1H is found naturally at high abundance, whereas the others must be introduced in proteins. Thus, it is necessary to find an expression system to introduce isotope into proteins. Generally, there are several approaches to express proteins and peptides: cell-based expression system, cell-free expression system, and chemical synthesis. The most widely used cell-based expression systems are: bacteria, yeasts, and insect cells (Table 1). Isotope labeling is possibly available in mammalian cells, but the cost for medium is too high. Creative Biostructure employs both prokaryotic and eukaryotic expression systems in uniformly or selectively labelled proteins.
Table 1. Cell-based isotope labeled protein production system
| E. coli | Yeast | Insect cells | Mammalian cells | |
| Ubiquitous labeling | 15N, 13C, 2H | 15N, 13C, | 15N, 13C- labeling is possible | 15N, 13C- labeling is possible |
| Medium | Ammonium salts as 15N-source, glucose as 13C-source | Ammonium salts as 15N-source, methanol as 13C-source | Minimal media | - |
Various isotope-labeling scheme in proteins for NMR studies:
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