Abstract:
:Class II MHC glycoproteins bind short (7-25 amino acid) peptides in an extended type II polyproline-like conformation and present them for immune recognition. Because empty MHC is unstable, measurement of the rate of the second-order reaction between peptide and MHC is challenging. In this report, we use dissociation of a pre-bound peptide to generate the active, peptide-receptive form of the empty class II MHC molecule I-Ek. This allows us to measure directly the rate of reaction between active, empty I-Ek and a set of peptides that vary in structure. We find that all peptides studied, despite having highly variable dissociation rates, bind with similar association rate constants. Thus, the rate-limiting step in peptide binding is minimally sensitive to peptide side-chain structure. An interesting complication to this simple model is that a single peptide can sometimes bind to I-Ek in two kinetically distinguishable conformations, with the stable peptide-MHC complex isomer forming much more slowly than the less-stable one. This demonstrates that an additional free-energy barrier limits the formation of certain specific MHC-peptide complex conformations.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Kasson PM,Rabinowitz JD,Schmitt L,Davis MM,McConnell HMdoi
10.1021/bi9921337subject
Has Abstractpub_date
2000-02-08 00:00:00pages
1048-58issue
5eissn
0006-2960issn
1520-4995pii
bi9921337journal_volume
39pub_type
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