Adsorption and helical coiling of amphipathic peptides on lipid vesicles leads to negligible protection from cathepsin B or cathepsin D.
The processing of antigenic peptides for presentation by MHC molecules to T cells, may depend upon the function of a second, consensus sequence in or near the T cell-presented epitope. One such processing-regulating sequence appears to be composed of amino acids Leu, Ile, Val, Phe, and Met recurring in a fashion to form a longitudinal, hydrophobic strip when the excised peptide is coiled as an alpha-helix. Such a hydrophobic strip-of-helix may: (a) scavenge peptides from lumens onto lipid membranes of digestion vesicles, (b) stabilize peptides there as protease-resistant helices, (c) specify recognition by the antigenic peptide-binding sites of chaperonin proteins, transmembranal transporters, or MHC molecules. By circular dichroism and electron paramagnetic resonance, we demonstrated that peptides with recurrent hydrophobic residues potentially forming longitudinal strips adsorbed to, and partially coiled as helices on, di-O-hexadecyl, D-L-alpha-phosphatidylcholine (DHPC) vesicles. Cathepsin B or cathepsin D cleavages of three such peptides were identified. With either enzyme, it made no significant difference whether a peptide substrate was in solution or bound to vesicles in terms of efficiency and specificity of peptide bond cleavages. We conclude that protease resistance, per se, of membrane-adsorbed, helically coiled peptides is not a major factor in the selection for T cell presentation of epitopes in peptides which have a motif with a longitudinal hydrophobic strip.
Department of Pharmacology, University of Massachusetts Medical School, Worcester 01655.
T G
TG
Goldschmidt
V E
VE
Reyes
G
G
You
D J
DJ
Nelson
P S
PS
Reisert
J
J
Anderson
J
J
Mole
R E
RE
Humphreys
D000327:Adsorption; D000595:Amino Acid Sequence; D000818:Animals; D000938:Antigen-Presenting Cells / Q000378:metabolism; D002401:Cathepsin B / Q000378:metabolism*; D002402:Cathepsin D / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D008081:Liposomes; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000187:drug effects; D010742:Phospholipid Ethers; D017433:Protein Structure, Secondary; D013379:Substrate Specificity
C052298:1,2-dihexadecyl-sn-glycero-3-phosphocholine; D008081:Liposomes; D010446:Peptide Fragments; D010742:Phospholipid Ethers; D002401:Cathepsin B; D002402:Cathepsin D