A polypeptide is a long chain of amino acids linked by peptide bonds, typically beyond 20-50 residues depending on adopted conventions. The boundary with oligopeptide is fuzzy, and that with proteins equally so: one generally speaks of a protein when the polypeptide adopts a stable, functional three-dimensional structure, often beyond 50-100 residues.
Polypeptides cover an immense functional range. Insulin (51 aa, two chains linked by disulfide bridges) is the historical example — the first peptide hormone sequenced by Sanger in 1955, and today one of the most prescribed drugs worldwide. GLP-1 peptides (30 aa), GIP (42 aa), glucagon (29 aa), PTH (84 aa), calcitonin (32 aa), ACTH (39 aa), and the active fragments of many hormones all belong to this category.
In modern peptide research, therapeutically relevant analogs are predominantly polypeptides: semaglutide (31 aa), tirzepatide (39 aa), retatrutide (39 aa), liraglutide (31 aa), exenatide (39 aa), teriparatide (34 aa). This size is necessary to faithfully reproduce the multiple interactions between peptide and transmembrane receptor, and to integrate structural modifications (lipidation, non-standard amino acid substitutions) that extend plasma half-life.
Long polypeptide synthesis represents a technical challenge: each SPPS coupling introduces impurities, and a 40-residue peptide synthesized with 99% yield per coupling drops to 67% crude purity before purification. Hence the crucial importance of thorough analytics (preparative HPLC, high-resolution LC-MS, identity testing via Edman sequencing or MS/MS fragmentation) to guarantee reproducible RUO quality.
Polypeptides thus form the technical and scientific top tier of a research catalog, justifying higher costs through manufacturing complexity and the sophistication of applications they enable.
Décryptez la caractérisation complète d'un peptide : RP-HPLC préparative et analytique, LC-MS haute résolution Orbitrap/QTOF, RMN 2D (COSY/TOCSY/NOESY), dégradation d'Edman, cartographie peptidique MS/MS, dichroïsme circulaire. Les 10 techniques qui séparent un peptide research-grade d'un peptide douteux, avec seuils de détection et stratégie de QC.
Maitrisez les mecanismes qui detruisent vos peptides : oxydation Met, deamidation Asn, hydrolyse, aggregation. Protocoles de lyophilisation, conditions de stockage, reconstitution optimale et QC shelf-life. Le pilier technique que tout laboratoire doit integrer pour garantir l'integrite de ses peptides en recherche exploratoire.
Principe Merrifield, stratégies Fmoc et Boc, résines (Wang, Rink amide, 2-chlorotrityl), agents de couplage (HBTU, HATU, DIC/HOBt), cycle de synthèse, clivage TFA, purification RP-HPLC, contrôle qualité LC-MS et test Kaiser. Le pilier scientifique de référence sur la fabrication des peptides synthétiques.