Protein precursor

Precursor protein (English precursor praecursor from latin, precursor '), and propeptides are inactive precursors of proteins. By at least one post-translational modification, an enzymatic cleavage of a peptide bond, can be converted into an active form The prefixes pro or prepro before the name of the protein characterize the precursor. Precursor proteins are initially formed in an inactive form and are activated by specific activation enzymes only when needed and in situ.

Function of the precursor peptide sequence

Generally, the precursor sequence prevents the activity of the protein, sometimes allosterically by this region pushes over approximately one active site or the conformation of the overall molecule so influenced that it will not be effective. In some cases ( insulin, collagen), these regions are required for the formation of the functional conformation of the tertiary structure. Often, the precursor protein is a form of transportation or a storage form represents the cleavage of a peptide sequence is usually associated with an interactive conformation.

Precursor protein groups

Prohormones

Precursor hormones are often referred to as pro-hormones, such as proinsulin, the precursor of insulin.

Proenzymes

Precursor enzymes are referred to as proenzymes or zymogens. Examples are digestive enzymes, clotting factors, specific proteinases such as procollagenase and some factors of the complement system.

Precursor structural proteins

Some structural proteins arise initially as inactive precursors, which only get their active rigid form in situ, such as collagen or silk protein fibroin.

Specific activation enzymes

Activation enzymes for specific cleavage of a precursor protein into a pro-peptide and an active protein are part of the post-translational modifications. As peptidases are hydrolases and include the EC 3.4. -. - To.

Examples:

The cleavage of procollagens done by procollagen peptidases. The enzyme procollagen N- endopeptidase ( EC 3.4.24.14 ) is required for the elimination of amino-terminal sequences, while the enzyme procollagen C- endopeptidase ( EC 3.4.24.19 ) cleaves carboxy-terminal procollagen sequences.

Activation by cleaving a peptide from the amino-terminal Pro- islet amyloid polypeptide ( proIAPP ) is carried out by the prohormone convertase enzyme (EC 3.4.21.93 ).