Contribution of proline residue for efficient production of MHC class I ligands by proteasomes.
Proteasomes are processing enzymes capable of generating major histocompatibility complex (MHC) class I ligands, but the mechanism of how they excise ligands without destroying them is largely unknown. Previously, we reported that most products of ornithine decarboxylase degraded in vitro by the 26 S ATP-dependent proteasome, which contained one or two Pro residues (Tokunaga, F., Goto, T., Koide, T., Murakami, Y., Hayashi, S., Tamura, T., Tanaka, K., and Ichihara, A. (1994) J. Biol. Chem. 269,17382-17385), which implied that the Pro residue has a role in the escape from random cleavage by proteasomes. Here, we examine the role of the Pro residue in producing MHC class I ligands in vitro. Proteasomes generated two cytotoxic T lymphocyte-epitopic precursor peptides, SIIPGLPLSL and DMYPHFMPTNL, from the 29-mer and 25-mer peptides harboring these sequences, which are derived from the c-akt proto-oncogene and the pp89 protein of mouse cytomagalovirus, respectively. Replacement of the first or second Pro residue within these epitopes by Ala resulted in a marked reduction of this epitope-derived production or their random cleavage by proteasomes, irrespective of the presence of PA28, which greatly accelerates the generation of unmodified ligands. Moreover, replacement of a single amino acid residue other than Pro in both epitopic and flanking regions by Ala or Leu had no or little appreciable effect on the SIIPGLPLSL or its derivative production. Thus, Pro residue(s) within these epitopic sequences presumably contributes to efficient production of MHC class I ligands through prevention of their random cleavage by proteasomes.
Biomedical R&D Department, Sumitomo Electric Industries, 1, Taya-cho, Sakae-ku, Yokohama 244-8588, Japan.
N
N
Shimbara
K
K
Ogawa
Y
Y
Hidaka
H
H
Nakajima
N
N
Yamasaki
S
S
Niwa
N
N
Tanahashi
K
K
Tanaka
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D003587:Cytomegalovirus / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D017874:Immediate-Early Proteins / Q000276:immunology; D016056:Immunodominant Epitopes; D008024:Ligands; D008099:Liver / Q000201:enzymology; D051379:Mice; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D011392:Proline; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000276:immunology; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D013379:Substrate Specificity; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology
D015395:Histocompatibility Antigens Class I; D017874:Immediate-Early Proteins; D016056:Immunodominant Epitopes; D008024:Ligands; D009097:Multienzyme Complexes; D009842:Oligopeptides; D011518:Proto-Oncogene Proteins; C052612:cytomegalovirus immediate early phosphoprotein pp89; D011392:Proline; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex