{'fraction_non_alphanumeric': 0.02004008016032064, 'fraction_numerical': 0.026052104208416832, 'mean_word_length': 5.456896551724138, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Large Scale Mass Spectrometric Sequencing of Peptides Eluted from HLA‐B35 Molecules Revealed Broad and N‐terminal Extended Peptide Motifs

HLA class I molecules present a large mixture of peptides with a distinct consensus peptide motif defined by a length of 8 to 10 amino acids with conserved residues at the C terminal and at one or two internal positions. Binding of peptides to the HLA class I molecule occurs in the endoplasmic reticulum and it has been suggested that a large proportion of peptides are transported to the endoplasmic reticulum as N‐terminal extended intermediates that are subsequently trimmed by an endoplasmic reticulum‐resident aminopeptidase. It is unclear whether N‐terminal trimming occurs prior or after peptide binding to the HLA molecule. In this study we used a large‐scale and highly sensitive mass spectrometric analysis of whole cell lysates to sequence over 1,000 peptides eluted from six different HLA‐B35 molecules (B3501, 3502, 3503, 3504, 3506, 3508). We demonstrated that the length distribution of HLA‐B35‐bound peptides is broad, and includes peptides of up to 18 residues. Remarkably, we identified several N‐terminal extended peptides which contained an appropriate HLA class I peptide motif internally. This finding provides evidence for the transport of N‐terminal extended peptide intermediates to the endoplasmic reticulum that can bind HLA class I molecules, followed by N‐terminal trimming to the appropriate HLA class I specific peptide motif.