Prepro proteins

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. 

Prepro-protein, a ribosomal synthesized protein bearing both the presequence and the prosequence. 

Fig. 3. Processing steps of rat and bovine prepro-vasopressin lea ding to the hormone vasopressin and its carrier protein, neurophysin (14). (a) Putative signal peptide (b) vasopressin (c) neurophysin (d) glycopeptide. CHO = carbohydrate.

Not only this heptapeptide but also the entire amino acid sequence of a-melanotropin is found within the sequence of corticotropin (Fig. 30-2), which has an additional 29 amino acids at the C-terminal end.25 The same heptapeptide was also found in the lipotropins. The explanation is, in part, that several of these hormones arise from a single 31-kDa precursor protein called prepro-opiomelanocortin.25 26 It contains an N-terminal signal sequence that is removed shortly after synthesis, as well as pairs of adjacent basic residues (Arg-Arg, Arg-Lys, Lys-Arg and Lys-Lys) at a number of places (Fig. 30-2). After removal of the... 

Both Met-enkephalin and Leu-enkephalin have their own pro- and prepro forms.29 Bovine preproenkephalin A is a 268-residue protein containing a 20-residue signal sequence and four sequences of Met-enkephalin and one of Leu-enkephalin, each flanked by pairs of basic residues. There are also Met-enkephalin-Arg-Gly-Leu (YGGFMRGL) and Met-enkephalin-Arg-Phe sequences. Not all of these are cut out cleanly, and other peptides such as Met-enkephalin-Arg-Arg-Val-NH2 are also found in brain. Proenkephalin B contains three copies of Leu-enkephalin contained within longer peptides. One of these, P-dynorphin (Table 30-4), is also a potent opioid compound. The enkephalins are thought to act as neurotransmitters, which are rapidly degraded after their release by two or three membrane-bound... 

Three distinct families of classical opioid peptides have been identified the enkephalins, endorphins, and dynorphins. Each family derives from a distinct precursor protein, prepro-opiome-lanocortin (POMC), preproenkephalin, and preprodynorphin, respectively, which are encoded by distinct genes. Each precursor is subject to complex cleavages and posttranslational modifications that result in the synthesis of multiple active peptides. The opioid peptides share a common amino-terminal sequence of Tyr-Gly-Gly-Phe-(Met or Leu), the opioid motif. This motif is followed by C-terminal extensions yielding peptides ranging from 5 to 31 residues (Table 21-1). 

Protein CPB 20, prepro-(tobacco clone cpb20-52 antifungal reduced) 2972a,4249... 

Dynorphins (Dyn), opioid peptides released from the precursor protein prepro-dynorphin, (prepro-enkephalin B). Dynorphin A (Dyn A), YGGFLRRIRP KLKWDNQ, dynorphin B (Dyn B), YG GFLRRDFK WT, a-neoendorphin (— neoendorphins), prodynorphin-derived... 

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