Propeptides

Collagen chains are synthesized as longer precursors, called procollagens, with globular extensions—propeptides of about 200 residues—at both ends. These procollagen polypeptide chains are transported into the lumen of the rough endoplasmic reticulum where they undergo hydroxylation and other chemical modifications before they are assembled into triple chain molecules. The terminal propeptides are essential for proper formation of triple... 

A six aminoacid neurotensin-like peptides synthesized in the same propeptide precursor as neurotensin. 

A major difference between the classical transmitters and peptides is that the production of a peptide is quite different since the synthesis of a peptide is in the form of a huge precursor of about 300 amino acids which is produced in the nucleus of the cell and then transported to the terminal being processed en route (Fig. 12.1). The prepropeptide is produced by translation in ribosomes and so occurs only in cell bodies or dendrites while the classical transmitters are produced at the terminal via a short series of enzymatic steps from a simple precursor. The study of the production of the propeptides have revealed a series of principles in that ... 

Some propeptides lead to the production of different, in terms of receptor affinities, peptides (substance P and neurokinin A act on neurokinin 1 and 2 receptors, respectively). 

Some propeptides produce multiple copies of similar peptides (met-enkephalin and leu-enkephalin act on the same delta opioid receptor). 

Upper panel The hydropathy profile of the entire 69 kD precursor protein is shown. The abscissa is amino acid residues and the ordinate, positive values indicate hydrophilic. The black and hatched rectangles at the bottom of the figure denote the calculated signal sequence and amino-terminal propeptide domains, respectively. The mature and carboxyl-terminal domains are labeled. N-linked core glycosylation consensus sites are depicted by branched structures. 

Figure 3. Schematic representation of the PGII, PGI, PGC [13] and PGE proteins from A. niger, indicating the putative processing sites for the signal peptide ( ) and the mono- and dibasic processing site for the propeptide ( ). The position of introns (lA, IB and IC) are indicated ( [) and variation of amino acids number is shown in different parts of protein. The putative N-glycosylation sites are marked ( ).

The MMPs are synthesized as preproproteins and are secreted as latent proproteins. Most MMPs share a common domain structure of a propeptide (about 80 amino acids) that has a conserved cysteine ligated to the catalytic zinc thus maintaining latency [10], a catalytic domain (about 180 amino acids), and a C-terminal domain (about 210 amino acids)... 

Fig. 2). Not all MMPs have these domains, for example, matrilysin lacks the C-terminal domain and the MT-MMPs do not have the propeptide. Some MMPs have additional domains, for example, the gelatinases have three repeats of a fibronectin-type II domain. 

Rosoff, M.L., Doble, K.E., Price, D.A. and Li, C. (1993) The flp-1 propeptide is processed into multiple, highly similar FMRFamide-like peptides in Caenorhabditis elegans. Peptides 14, 331—338. 

Neuropeptides are packaged into large, dense-core vesicles 325 Diversity is generated by families of propeptides, alternative splicing, proteolytic processing and post-translational modifications 326... 

Prepro proteins are synthesized with a signal peptide, which directs the protein to the endoplasmic reticulum, where the signal peptide is cleaved thereafter the propeptide is excized and the mature protein or peptide secreted into the circulation. 

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