Peptide-Ready MHC: FAQs

Frequently Asked Questions regarding our Peptide-Ready MHCs for custom peptide loading.

1. What is a prMHC? 
   1. prMHC is a 'peptide-ready MHC' that doesn’t contain any pre-loaded peptide and can be loaded with custom peptides for TCR binding and cell staining. 
2. Is prMHC a propriety design from KACTUS?
   1. Yes, prMHC is a propriety design based on our SAMS™ Protein Engineering Platform.
3. Is prMHC a single-chain design?
   1. Yes, prMHC is a single-chain design of α-chain and β-2 microglobulin by our protein engineering team.
4. Is prMHC purified from mammalian cells?
   1. Yes, prMHC is purified from Expi293.
5. How is prMHC purified?
   1. PrMHC is affinity purified via His tag at the C-terminus with additional size exclusion chromatography steps.
6. What prMHC products does KACTUS provide?
   1. KACTUS provides prMHC monomer, biotinylated monomer, and fluorescent tetramer. 
7. What is prMHC monomer?
   1. prMHC monomer consists of α-chain and β-2 microglobulin, a single subunit of prMHC tetramer.
8. What is prMHC biotinylated monomer?
   1. It is prMHC monomer with biotin at C-terminal Avi tag.
9. What is fluorescent prMHC tetramer?
   1. Fluorescent prMHC tetramer has fluorophores conjugated to each monomer subunit of the complex.
10. How are prMHC products QC’d? 
    1. We analyze prMHC products by Tris-Bis PAGE, SEC-HPLC, endotoxin level, peptide-loading and functionality tests.
11. Which fluorophores are available for prMHC tetramer?
    1. We currently offer APC-equivalent, FITC-equivalent and PE conjugation for prMHC tetramer.
12. What are the properties of APC-equivalent fluorophores?
    1. APC-equivalent is 90 kDa protein, with excitation peak at 609 nm and emission peak at 643 nm.
13. Is APC-equivalent labeled in vitro to prMHC tetramer?
    1. No, APC-equivalent is an in vivo label, part of the single chain design for fluorescent prMHC tetramer. 
14. Is prMHC tetramer made by in vitro assembly by streptavidin? 
    1. No, prMHC tetramerizes in vivo during expression in Expi293, a KACTUS propriety design.
15. Does KACTUS provide custom prMHC I and prMHC II? 
    1. Yes, KACTUS provides custom prMHC I and II for all available MHC alleles. 
16. What is the lead time for custom prMHC services?
    1. The lead time is 6 to 8 weeks. 
17. How do I order custom MHC?
    1. Go to our website and fill out a custom order request form, or email us at order@kactusbio.us  
18. Can you provide a prMHC peptide loading protocol?
    1. Yes, contact support@kactusbio.us for a protocol.
19. Can KACTUS prMHC be used for peptide screening? 
    1. Yes, KACTUS prMHC can be used for peptide screening. 
20. Can you provide a tetramer staining protocol using prMHC?
    1. Yes, contact support@kactusbio.us for a protocol.
21. What is the shelf life of prMHC?
    1. prMHC can be stored for at least 12 months at -80°C.