A protein precursor, also called a pro-protein or pro-peptide, is an inactive
protein (or
peptide) that can be turned into an active form by
post-translational modification, such as breaking off a piece of the
molecule or adding on another molecule. The name of the precursor for a protein is often prefixed by ''pro-''. Examples include
proinsulin and
proopiomelanocortin, which are both
prohormones.
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 precursors are called
zymogens or
proenzyme
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 active ...
s. 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
A signal peptide (sometimes referred to as signal sequence, targeting signal, localization signal, localization sequence, transit peptide, leader sequence or leader peptide) is a short peptide (usually 16-30 amino acids long) present at the N-ter ...
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
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
.
An example is
preproinsulin.
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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