Ser21

Ser21 is a designation used in various scientific contexts to refer to serine-related elements at position 21 or to a specific gene or protein identifier. Because it appears in multiple annotation systems, its exact meaning depends on the context and database being referenced.

In protein sequence notation, Ser21 typically denotes the serine residue at position 21 within a given protein. This shorthand is common in sequence alignments, mutation analyses, and discussions of post-translational modifications, such as phosphorylation at serine 21 (Ser21). When reporting mutations, Ser21 may be written as Ser21X, where X is the substituting amino acid, to indicate a change at that position.

In genetics and genomics, Ser21 can appear as a gene symbol or open reading frame (ORF) name in certain organisms or databases. The usage is not universal, and some databases will instead assign distinct gene identifiers that do not rely on residue-based numbering. In structural and proteomic databases, Ser21 may also be encountered as a residue index in protein structures or peptide identifications, where it helps locate a specific serine within a modeled chain or sequence.

Because Ser21 has multiple potential meanings, researchers should consult the original source to determine whether it refers to a residue position in a protein, a gene/ORF label, or another context. Disambiguation may involve checking database headers, organism-specific nomenclature, or accompanying sequence or structural data.