S. Malarkannan et al., THE ROLE OF MHC CLASS-I MOLECULES IN THE GENERATION OF ENDOGENOUS PEPTIDE MHC COMPLEXES/, The Journal of immunology, 154(2), 1995, pp. 585-598
Cellular proteins undergo proteolysis to yield peptide/MHC class I com
plexes for display on the APC surface. During this process it is not c
lear whether MHC molecules bind to and stabilize independently generat
ed peptides, or whether they are involved in the peptide cleavage even
ts. In this study, we analyzed the role of MHC molecules in Ag process
ing by characterizing the naturally processed peptide analogues of OVA
(OVA257-264, SL8) in APC. DNA constructs encoding SL8 precursors were
transfected into cells that varied in their MHC expression. By HPLC f
ractionation of cell extracts and with sensitive T cell assays for bot
h the processed SL8 and its minimal Met-SL8 (MSL8) precursor, we deter
mined that expression of K-b MHC molecule was essential for detecting
processed peptides in living cells. Curiously, although the translated
MSL8 nonapeptide precursor itself could bind K-b as well as the SL8 o
ctapeptide, and MSL8 was available to MHC, only the SL8 peptide was fo
und in K-b cell extracts. The presence of naturally processed SL8, but
not MSL8 peptide in K-b-expressing cells suggests that the precise id
entity of endogenously processed peptides is also strongly influenced
by the MHC molecules.