Ser33

Ser33 is a residue designation used in protein sequence annotations to refer to a serine located at position 33 within a polypeptide chain. It is not a standalone molecule but a way to describe a specific location in a protein’s sequence. Residue numbering typically starts with the initiating methionine, and in some contexts—such as mature forms after the removal of signal peptides—the numbering can shift, so Ser33 may refer to different positions depending on the sequence reference used.

Serine residues are common sites for post-translational modification, most notably phosphorylation by serine/threonine kinases. As a result, Ser33 can be a potential regulatory site in proteins where the local context supports such modification. The functional significance of Ser33 is highly protein-specific and must be established for each individual protein through experimental study.

Detection and annotation of Ser33 are routinely performed using mass spectrometry, peptide sequencing, and curated databases. Resources like UniProt and phosphorylation-focused databases document observed instances of Ser33 modification when supported by evidence. Mutagenesis experiments, such as substituting serine with alanine or aspartate (for example S33A or S33D variants), are commonly used to investigate its role in activity, stability, or interactions, though outcomes vary across systems.

Because Ser33 is a generic positional label rather than a unique molecule, its biological importance is determined by the protein context. It serves as a precise reference point for researchers studying structure, function, and regulation at that site.