Precursor proteins

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Post-translational biosynthesis from preproinsulin via proinsulin to insulin

Protein precursor ( English precursor from latin precursor , precursor '), and propeptides or pre-proteins are inactive precursors of proteins obtained by at least one post-translational modification , a proteolytic cleavage of a peptide bond are converted into an active form. The prefixes pro or prepro in front of the name of the protein identify the precursor. Precursor proteins are initially created in an inactive form and are only activated when required and in situ by specific activation enzymes.

Function of the precursor peptide sequence

In general, the precursor sequence prevents the activity of the protein, sometimes allosterically , for example by pushing this area over an active center or by influencing the conformation of the entire molecule in such a way that it is not effective. In some cases (insulin, collagen) these areas are necessary for the functional development of the conformation of the tertiary structure . The precursor protein often represents a transport form or a storage form. The cleavage of a peptide sequence is usually accompanied by an interactive change in conformation .

Precursor protein groups

Prohormones

Precursor hormones are also often referred to as prohormones , such as proinsulin , the precursor of insulin .

Proenzymes

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

Precursor structural proteins

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

Specific activation enzymes

Activation enzymes for the specific cleavage of a precursor protein into a propeptide and an active protein are part of the post-translational modifications. As peptidases, they are hydrolases and belong to EC  3.4.-.- .

Examples:

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

Activation by splitting off an amino-terminal peptide from the pro-islet cell amyloid polypeptide (proIAPP) is carried out by the prohormone convertase enzyme ( EC  3.4.21.93 ).

Individual evidence

  1. ^ Cleavage on a pair of basic residues. In: UniProt Keywords. UniProtKB, accessed on September 10, 2010 : “Definition. Protein which is posttranslationally modified by the cleavage on at least one pair of basic residues, in order to release one or more mature active peptides (such as hormones). "
  2. ↑ Edward J. Campbell, J. Davis Cury, Cathy J. Lazarus, and Howard G. Welgus: Monocyte procollagenase and tissue inhibitor metalloproteinases. Identification, characterization, and regulation . (PDF) In: The Journal of Biological Chemistry . 262, No. 33, November 25, 1987, pp. 15862-15868. Retrieved March 3, 2013.
  3. ↑ Charles M. Lapière, Albert Lenaers, and Leonard D. Kohn: Procollagen peptidase: An enzyme excising the coordination peptides of procollagen . In: Proc Natl Acad Sci US A. . 68, No. 12, December 1971, pp. 3054-3058. PMC 389589 (free full text).
  4. ↑ Jing Wang, et al. : The prohormone convertase enzyme 2 (PC2) is essential for processing pro-islet amyloid polypeptide at the NH 2 -terminal cleavage site . In: diabetes . 50, No. 3, March 2001, pp. 534-539. doi : 10.2337 / diabetes.50.3.534 . Retrieved March 3, 2013.