Protein Cys-A/G
Description
Cysteine (Cys) in Proteins: Core Functions and Modifications
Cysteine, a semiessential amino acid (HO₂C–CH(NH₂)–CH₂–SH), is critical for protein structure and function due to its thiol (-SH) group. Key roles include:
Key Data:
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Conservation: Cys residues are highly conserved, ranking among the most conserved amino acids (e.g., Gly, Pro, Trp) in proteins .
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Abundance: Cys constitutes ~2.2% of human proteomes, with dense clustering in extracellular proteins (e.g., EGF-like domains) .
Potential Interpretations of "Cys-A/G"
Given the absence of direct references, possible interpretations include:
Hypothesis 1: Cysteine-Modified Proteins
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Post-translational modifications: Cys residues undergo S-nitrosylation, persulfidation, or palmitoylation, altering protein localization and function .
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Engineered variants: Site-specific Cys mutations (e.g., C→A/G substitutions) to study redox roles or protein folding.
Hypothesis 2: Cystine Knots or Networks
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Cystine-rich domains: Proteins like SCO-spondin (563 Cys residues) form complex disulfide networks critical for structural integrity .
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Interchain disulfides: Enable multimerization (e.g., keratin-associated proteins) .
Cysteine Interactions with Nanoparticles
Research on protein-Cys interactions with silver nanoparticles (AgNPs) highlights thiol reactivity:
| Protein | Cys Content | AgNP Interaction | Outcome |
|---|---|---|---|
| GB3 (Cys₀) | 0 | Carboxylate binding | No dissolution |
| GB3 (Cys₁) | 1 | Thiolate binding | Partial dissolution |
| GB3 (Cys₂) | 2 | Strong thiolate coordination | Complete dissolution |
Key Findings:
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Free Cys residues drive AgNP dissolution via thiolate-Ag binding, while oxidized Cys (e.g., in disulfides) show minimal reactivity .
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Steric hindrance in globular proteins limits Cys-Ag interactions, unlike in linear peptides .
Subcellular Redox Regulation
Disease Implications
Cys dysregulation is linked to:
Database Resources for Cys Proteomics
Tools like Cys.sqlite catalog Cys residues in PDB structures, enabling analysis of:
Product Specs
Product Science Overview
The recombinant Protein A/G is composed of:
- Five IgG-binding regions of Protein A: These regions are derived from the segments E, D, A, B, and C of the Protein A from Staphylococcus aureus .
- Two IgG-binding regions of Protein G: These regions are derived from the segments C1 and C3 of the Protein G from Streptococcus .
The recombinant protein is produced in Escherichia coli and is typically available as a sterile filtered, white lyophilized (freeze-dried) powder .
Protein A/G has a broader binding capacity than either Protein A or Protein G alone. It binds to various human, mouse, and rat IgG subclasses, including:
- Human IgG1, IgG2, IgG3, IgG4
- Mouse IgG2a, IgG2b, IgG3
- Rat IgG2a, IgG2c
Additionally, it binds to total IgG from other species such as cow, goat, sheep, horse, rabbit, guinea pig, pig, dog, and cat .
The recombinant Protein A/G is ideal for the purification of monoclonal or polyclonal IgG antibodies. It is commonly used in:
- Affinity chromatography: For the purification of antibodies from various species.
- Immunoprecipitation: To isolate specific proteins from complex mixtures.
- Western blotting: As a detection reagent for IgG antibodies.
The lyophilized Protein A/G is stable at room temperature for up to three weeks. For long-term storage, it should be kept desiccated below -18°C. Upon reconstitution, it should be stored at 4°C for short-term use (2-7 days) and below -18°C for long-term use. It is recommended to add a carrier protein (0.1% HSA or BSA) to prevent freeze-thaw cycles .
