The proteolytic fragments generated by vertebrate proteasomes: structural relationships to major histocompatibility complex class I binding peptides.

AUTOR(ES)

Niedermann, G

RESUMO

Proteasomes are involved in the proteolytic generation of major histocompatibility complex (MHC) class I epitopes but their exact role has not been elucidated. We used highly purified murine 20S proteasomes for digestion of synthetic 22-mer and 41/44-mer ovalbumin partial sequences encompassing either an immunodominant or a marginally immunogenic epitope. At various times, digests were analyzed by pool sequencing and by semiquantitative electrospray ionization mass spectrometry. Most dual cleavage fragments derived from 22-mer peptides were 7-10 amino acids long, with octa- and nonamers predominating. Digestion of 41/44-mer peptides initially revealed major cleavage sites spaced by two size ranges, 8 or 9 amino acids and 14 or 15 amino acids, followed by further degradation of the latter as well as of larger single cleavage fragments. The final size distribution was slightly broader than that of fragments derived from 22-mer peptides. The majority of peptide bonds were cleaved, albeit with vastly different efficiencies. This resulted in multiple overlapping proteolytic fragments including a limited number of abundant peptides. The immunodominant epitope was generated abundantly whereas only small amounts of the marginally immunogenic epitope were detected. The frequency distributions of amino acids flanking proteasomal cleavage sites are correlated to that reported for corresponding positions of MHC class I binding peptides. The results suggest that proteasomal degradation products may include fragments with structural properties similar to MHC class I binding peptides. Proteasomes may thus be involved in the final stages of proteolytic epitope generation, often without the need for downstream proteolytic events.

Documentos Relacionados

• Single-residue changes in class I major histocompatibility complex molecules stimulate responses to self peptides.
• Alloantibodies can discriminate class I major histocompatibility complex molecules associated with various endogenous peptides.
• Reassociation with beta 2-microglobulin is necessary for Kb class I major histocompatibility complex binding of exogenous peptides.
• Identification of two distinct properties of class II major histocompatibility complex-associated peptides.
• Primitive synteny of vertebrate major histocompatibility complex class I and class II genes