Editing Protein splicing (section)

{{Short description|The post-translational removal of peptide sequences from within a protein sequence}}
[[File:intein mech.png|thumb|upright=1.25|alt=mechanism of protein splicing involving inteins|The mechanism of protein splicing involving inteins. In this scheme, the N-extein is shown in red, the intein in black, and the C-extein in blue. X represents either an oxygen or sulfur atom.]]
'''Protein splicing''' is an intramolecular reaction of a particular [[protein]] in which an internal protein segment (called an '''intein''') is removed from a precursor protein with a ligation of [[C-terminus|C-terminal]] and [[N-terminus|N-terminal]] external proteins (called [[extein]]s) on both sides. The splicing junction of the precursor protein is mainly a [[cysteine]] or a [[serine]], which are [[amino acid]]s containing a [[Nucleophile|nucleophilic]] [[side chain]]. The protein splicing reactions which are known now do not require exogenous cofactors or energy sources such as [[adenosine triphosphate]] (ATP) or [[guanosine triphosphate]] (GTP). Normally, '''splicing''' is associated only with [[Splicing (genetics)|pre-mRNA splicing]]. This precursor protein contains three segments—an '''N-extein''' followed by the intein followed by a '''C-extein'''. After splicing has taken place, the resulting protein contains the N-extein linked to the C-extein; this splicing product is also termed an extein.