Native sequence means a peptide whose amino acid order matches the molecule as it occurs naturally in a specified organism, with no substitutions, terminal caps, truncations or conjugates. The species qualifier is essential: human, rat and porcine versions of the same hormone frequently differ by one or more residues, and a peptide can be native to one and an analog relative to another.
Why native sequence matters in peptide research
Native material is the appropriate reference when the question concerns endogenous biology — receptor characterisation, antibody generation, assay standards, or establishing a baseline against which a modified molecule is compared. Catalogue examples include oxytocin, LL-37 and glutathione, all supplied as the naturally occurring sequence.
Native does not imply robust. Endogenous signalling peptides are typically built for rapid clearance, so their unmodified forms carry very short half-lives — native GLP-1 lasts about two minutes against roughly a week for its engineered analog. Nor does native imply post-translational fidelity: a synthetic native sequence lacks any glycosylation or phosphorylation present in vivo unless it was deliberately introduced. Compare recombinant and synthetic production; see reading a sequence.