A protein precursor, also called a pro-protein or pro-peptide, is an inactive
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
(or
peptide
Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
...
) that can be turned into an active form by
post-translational modification
Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribos ...
, such as breaking off a piece of the
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
or adding on another molecule. The name of the precursor for a protein is often prefixed by ''pro-''. Examples include
proinsulin
Proinsulin is the prohormone precursor to insulin made in the beta cells of the islets of Langerhans, specialized regions of the pancreas. In humans, proinsulin is encoded by the ''INS'' gene. The islets of Langerhans only secrete between 1% and ...
and
proopiomelanocortin
Pro-opiomelanocortin (POMC) is a precursor polypeptide with 241 amino acid residues. POMC is synthesized in corticotrophs of the anterior pituitary from the 267-amino-acid-long polypeptide precursor pre-pro-opiomelanocortin (pre-POMC), by the ...
, which are both
prohormone
A prohormone is a committed precursor of a hormone consisting of peptide hormones synthesized together that has a minimal hormonal effect by itself because of its expression-suppressing structure, often created by protein folding and binding additi ...
s.
Protein precursors are often used by an organism when the subsequent protein is potentially harmful, but needs to be available on short notice and/or in large quantities.
Enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
precursors are called
zymogen
In biochemistry, a zymogen (), also called a proenzyme (), is an inactive precursor of an enzyme. A zymogen requires a biochemical change (such as a hydrolysis reaction revealing the active site, or changing the configuration to reveal the activ ...
s or
proenzymes. Examples are enzymes of the digestive tract in humans.
Some protein precursors are secreted from the cell. Many of these are synthesized with an N-terminal
signal peptide that targets them for secretion. Like other proteins that contain a signal peptide, their name is prefixed by ''pre''. They are thus called pre-pro-proteins or pre-pro-peptides.
The signal peptide is cleaved off in the
endoplasmic reticulum.
An example is
preproinsulin
Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...
.
Pro-sequences are areas in the protein that are essential for its correct folding, usually in the transition of a protein from an inactive to an active state. Pro-sequences may also be involved in pro-protein transport and secretion.
Pro-domain (or prodomain) is the domain of a proprotein.
References
External links
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