A New Prosomatostatin-Derived Peptide Reveals a Pattern for Prohormone Cleavage at Monobasic Sites

Abstract

Cleavage of the peptide bonds of preprosomatostatin at basic residues near the carboxyl terminus yields somatostatin-14, somatostatin-28, and somatostatin-28 (1-12). However, little is known about the molecular forms derived from the amino terminal portion of the precursor, even though this part of the prohormone is highly conserved through evolution. By using an antibody against the amino terminus of prosomatostatin, a decapeptide with the structure Ala-Pro-Ser-Asp-Pro-Arg-Leu-Arg-Gln-Phe, corresponding to preprosomatostatin (25-34), was isolated from the endocrine portion of the rat stomach, the gastric antrum. The antral decapeptide may represent a bioactive product generated from prosomatostatin after a monobasic cleavage similar to that involved in the formation of somatostatin-28. In fact, a monobasic cleavage requires two basic residues and a domain containing nonpolar amino acids such as alanine or leucine, or both.

Disparate Intracellular Processing of Human IL-12 Preprotein Subunits: Atypical Processing of the P35 Signal Peptide

“…Consequently, the second site of cleavage must occur amino terminal to this residue. Upon closer examination of the amino acid sequence around R ϩ1 , we noted that the sequence conformed to a monobasic cleavage recognition site, as proposed by Benoit et al (20) and more recently by Devi (21); namely, there is H at the Ϫ5 position and L and A immediately precede the single R cleavage site. Using site-directed mutagenesis we showed that reducing the length and pK a of the basic amino acid side chain (L) diminished, while removing the functional group altogether (G) abrogated, secretion, demonstrating the importance of this functional group in cleavage and/or site recognition.…”

“…Since cleavage within the mid-h-region of the secretory peptide would not release a protein with an amino terminus comparable to that of the mature protein, we hypothesized that a second cleavage must have occurred after exiting the ER. Additional sequence analysis revealed that the c-region of the signal peptide resembled a monobasic protease recognition site, with cleavage predicted for the N-terminus of R ϩ1 : 1) cleavage occurs at R; 2) there is H at the Ϫ5 position; and 3) L and A are present immediately preceding the single R cleavage site (20,21). Therefore, we examined this possibility using site-directed mutagenesis (Fig.…”

Post‐translational processing of prepro‐urotensin II

“…In the case of processing at the site of multiple basic residues, the cleavage sites are often located inside, or immediately adjacent to, regions with a high probability of ~'-turn formation [11] or alternatively are associated with f/ loops [12]. Schwartz has identified proximity to proline residues as an important conformational feature regulating cleavage at single arginine residues in some precursor peptides [13] whereas Benoit et al have claimed that the monobasic site must be in a domain containing an additional basic residue together with leucine and/or alanine residues [14]. Isolation of flounder prourotensin II-(1-20)-peptide, which contains a COOHterminal arginine residue, identifies the site of cleavage of the signal peptide and provides good evidence that the precursor is cleaved a monobasic processing site.…”

Proteins of the Golgi apparatus

“…First, a large number of proteins are known to be proteolyzed within the endomembrane system, at sites separate from signal peptidase cleavage. These include the endoproteolytic processing of, for example, proalbumin (Dugaiczyk et al, 1982), proinsulin (Nolan et al, 1971), interleukin 3 (Fung et al, 1984;Yokota et al, 1984), prosomatostatin (Benoit et al, 1988;Lepage-Lezin et al, 1991 ;Goodman et al, 1983), prodynorphin (Devi et al, 1989;Civelli et al, 1985), and the procorticotropidendorphin precursor (Schnabel et al, 1989). These cleavages occur on either side of dibasic pairs of amino acids, such as Arg-Arg or Lys-Arg, or on the COOH- (Benoit et al, 1988;Fung et al, 1984) or NH,-terminal side (Devi et al, 1989;Civelli et al, 1985) of monobasic residues, usually Arg, in a number of processed proteins.…”

“…These include the endoproteolytic processing of, for example, proalbumin (Dugaiczyk et al, 1982), proinsulin (Nolan et al, 1971), interleukin 3 (Fung et al, 1984;Yokota et al, 1984), prosomatostatin (Benoit et al, 1988;Lepage-Lezin et al, 1991 ;Goodman et al, 1983), prodynorphin (Devi et al, 1989;Civelli et al, 1985), and the procorticotropidendorphin precursor (Schnabel et al, 1989). These cleavages occur on either side of dibasic pairs of amino acids, such as Arg-Arg or Lys-Arg, or on the COOH- (Benoit et al, 1988;Fung et al, 1984) or NH,-terminal side (Devi et al, 1989;Civelli et al, 1985) of monobasic residues, usually Arg, in a number of processed proteins. Enzymes catalyzing these cleavages have been described in a late Golgi compartment of yeast (the Kex2 protease, Redding et al, 1991;Wilcox and Fuller, 1991), in rat liver Golgi membranes (Mizuno et al, 1989;Brennan and Peach, 1988) and in the Golgi apparatus of rat neural (Lepage-Lezin et al, 1991) and pituitary cells (Schnabel et al, 1989).…”