A subset of HLA-B27 molecules contains peptides much longer than nonamers.
An unusual monoclonal antibody (MARB4) directed against HLA-B27 that reacts with only approximately 5-20% of the cell surface HLA-B27 was used for large-scale purification of these molecules. Subsequent mass spectrometry of HLA-B27-bound peptides showed that the minor MARB4-reactive population contained peptides primarily from 900 to 4000 Da in size (approximately 8-33 amino acid residues), whereas the major HLA-B27 population contained peptides in the mass range of 900-1400 Da (approximately 8-12 amino acid residues). Thus, a subset of HLA-B27 molecules binds to peptides much longer than nonamers. Typical HLA-B27-binding peptides contain arginine in position 2. Further analysis by Edman sequencing of the pooled bound peptides revealed that the major population contained substantial amounts of arginine at positions 1 and 9 (40-50%) and exclusively arginine at position 2, as expected. The minor population of peptides also contained detectable amounts of arginine at these positions, but at the level of only approximately 10%; no marked enrichment at any position was observed. These long HLA-B27-bound peptides could represent either intermediates in the formation of nonamers or adventitiously bound peptides. Lastly, in the TAP2 mutant cell line BM36.1 transfected with HLA-B*2705, MARB4-reactive HLA-B27 molecules were absent from the cell surface, indicating that the peptide transporter was required for delivery of the long peptides. Thus, during the folding of class I heavy chains, peptides of diverse lengths are available and participating.
Urban
R G
RG
Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, MA 02138.
Chicz
R M
RM
Lane
W S
WS
Strominger
J L
JL
Rehm
A
A
Kenter
M J
MJ
UytdeHaag
F G
FG
Ploegh
H
H
Uchanska-Ziegler
B
B
Ziegler
A
A
D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D001402:B-Lymphocytes / Q000276:immunology*; D002352:Carrier Proteins / Q000235:genetics; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D015796:HLA-B27 Antigen / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D017421:Sequence Analysis; D014162:Transfection
D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; D015796:HLA-B27 Antigen; D000949:Histocompatibility Antigens Class II; D010455:Peptides; C071692:TAP2 protein, human