25residue

25residue is a term used in biochemistry and molecular biology to denote a polypeptide chain consisting of 25 amino acid residues. The descriptor is length-based and is commonly used when discussing model peptides, folding studies, and sequence design. In practice, a 25-residue peptide can be linear or may include modifications at the N- or C-terminus.

The exact mass depends on amino acid composition, but a rough estimate for a 25-residue peptide is about 2.7 to 2.9 kilodaltons. Each residue contributes approximately 110 Da on average, and the final peptide includes the terminal groups which add about 18 Da. Scientists often calculate theoretical masses using standard residue masses, then confirm with mass spectrometry.

25residue peptides are routinely synthesized by solid-phase peptide synthesis (SPPS) using Fmoc chemistry, followed by purification by high-performance liquid chromatography and characterization by electrospray or MALDI-TOF mass spectrometry. They serve as simple models to study folding, helix formation, and peptide-protein interactions. They are also used as benchmarks in methods development.

In computational contexts, the term can describe a sequence window of 25 residues in a protein sequence, or as an identifier for a 25-residue synthetic construct in databases and simulations. The concept helps standardize comparisons of length-dependent properties such as hydrophobicity, propensity for secondary structure, or conformational sampling.

Overall, 25residue serves as a concise label in experimental design and computational analyses for a shared reference to a 25-residue segment.