Peptide nomenclature and sequence notation reference

A peptide paper opens with a sequence, and the sequence is the first place a reader either reads the molecule correctly or misreads it. GLP-1(7-36)amide and GLP-1(7-37) are the same precursor cleaved one residue apart at the C-terminus; semaglutide and liraglutide share a 31-residue backbone and differ in three structural moves — an Aib at position 8, an Arg at position 34, a C18 versus C16 fatty diacid on Lys26 — that take the plasma half-life from 13 hours to a week. The molecule a paper claims to describe is encoded in those parentheses, hyphens, and subscript-letter prefixes. The peptide literature does not pause to teach the convention; it assumes the reader already knows.

This dossier is the rosetta stone for the peptide papers on this site: amino acid abbreviations as fixed by the IUPAC-IUB Joint Commission on Biochemical Nomenclature, sequence directionality, termination modifications, D-amino acid and non-proteinogenic substitutions, lipid-conjugate and PEG modifications that define the modern long-acting class, cyclization conventions, glycosylation and PTM annotations, truncation and numbering rules, and the WHO INN suffix system. Tables anchor the glossaries; worked examples on real molecules anchor the structural conventions.