Protein Standards

CIL offers a variety of isotope-labeled recombinant proteins from Nexomics Biosciences, Inc. for use as standards in MS and NMR research. In MS-based studies, these proteins (e.g., 15N C-reactive protein) can be added to samples at the beginning of experimental workflows to help control/correct for analytical variability. The use of heavy proteins in MS experiments is commonly toward enhanced, and more accurate, protein quantification. In NMR spectroscopy, protein standards (e.g., labeled ubiquitin) are often used to assess NMR spectrometer performance, aid in the development of new pulse sequences, and for training purposes. Ubiquitin (NEX-UB1) is a small 8.8 kDa monomeric protein for which multiple sets of resonance assignments (BMRB database) and 3D structures (PDB database) are publicly available. This protein standard is uniformly 15N/13C-enriched, and ubiquitin has been used as an industry-wide standard in the protein NMR field for many years.

Related Resources

➤ Stable Isotope Standards for Mass Spectrometry
➤ Stable Isotope-Labeled Peptide and Protein Reagents/Kits

Stable Isotopes for Biomolecular NMR

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Isotope Label

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Isotopic Enrichment Range

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Molecular Weight Range

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Product Form 2

Maltose Binding Protein (NEX-MBP)

NEX-MBP is a 44.9 kDa monomeric protein for which multiple sets of resonance assignments (BMRB database) and 3D structures (PDB database) are publicly available. This product is uniformly 2H, 15N, 13C-enriched with selective incorporation of protons into methyl groups of Ile-δ1, Leu-δ and Val-γ side chains. As nonuniform sampling (NUS) and other NMR techniques emerge to push the size limitations of NMR to new boundaries, large protein standards, such as NEX-MBP, will be required to test data-collection and processing strategies.

Ubiquitin (NEX-UB1)

NEX-UB1 is a small 8.8 kDa monomeric protein for which multiple sets of resonance assignments (BMRB database) and 3D structures (PDB database) are publicly available. This protein standard is uniformly 15N/13C-enriched. Ubiquitin has been used as an industry-wide standard in the protein NMR field for many years.

X-Filtered NOESY NMR Standard (NEX-XF1)

In an X-filtered experiment, only NOEs between 15N/13C-1H and 14N/12C-1H (e.g., interchain NOEs) protons are observed. NOEs between protons connected to 15N/13C are filtered (intrachain NOEs). When uniformly double-labeled protein sample is mixed with a natural-abundance protein sample, the interface will give rise to the only observable NOESY cross peaks. This powerful strategy enables the spectroscopist to discern intra- from inter-NOESY cross peaks, thereby providing essential distance constraints for defining the dimer interface (Lee, et al., 1994, 350, 87; Palmer, et al., 1991, 93, 151; Schleucher, et al., 1994, 4, 301).

NEX-XF1 is a 16 kDa protein (A. fulgidus antitoxin vapB21 homodimer) for which a set of resonance assignments (bmr7362), 3D structure (2NWT), and other NMR data are available in the public domain. This is a mixture of unlabeled and uniformly 15N/13C-enriched protein (25% homodimer unlabeled; 50% heterodimer unlabeled/labeled; 25% homodimer labeled) and is perfect to set up X-filtered NOESY experiments.

Frequently Asked Question

I do not see my protein of interest; does CIL offer custom labeled proteins? Yes, we have the ability to customize. We would first review feasibility and then provide a quotation on your specific protein. To start this process, please provide the necessary details on the Custom Synthesis Request form or contact your local sales representative.