Signal peptidase enzymes

AM-001, and mannanase B properties are similar to those of P-mannanase M-III. Furthermore, the Ouchterlony double diffusion test showed that these five enzymes gave fused precipitation lines. However, N-terminal amino acid sequences of the five mannanases determined by an automatic amino acid sequencer revealed that the N-terminal amino acid sequence from amino acid 1 (Asn) to 9 (Gin) of the Bacillus sp. AM-001 enzymes coincides with those from amino acid 4 (Asn) to 12 (Asn) of the R coll JMlOl (pMAH3) enzymes as shown in Fig. 4. This may reflect differences in the specificities of the signal peptidases of the two bacteria. 

This enzyme [EC 3.4.21.89], also known as signal peptidase I and phage-procoat-leader peptidase, catalyzes the hydrolysis of N-terminal leader sequences from secreted and periplasmic protein precursors. It acts on a single bond Ala-Ala in the m-13 phage procoat protein and creates the signal (leader) peptide and coat protein. It is a member of the peptidase family S26 but is unaffected by inhibitors of most serine peptidases. 

This enzyme [EC 3.4.99.35] (better known as signal peptidase II and also known as bacterial leader peptidase I) catalyzes the cleavage of N-terminal leader sequences from membrane prolipoproteins. 

Among these are the well-known E. coli leader peptidase355 356 and other signal peptidases.357 These are integral membrane proteins that cleave N-terminal signal sequences from proteins incorporated into plasma membranes. Another enzyme of this class is the lexA repressor and protease discussed in Chapter 28. 

Processing of insulin. Insulin is synthesized by membrane-bound polysomes in the /3 cells of the pancreas. The primary translation product is preproinsulin, which contains a 24-residue signal peptide preceding the 81-residue proinsulin molecule. The signal peptide is removed by signal peptidase, cutting between Ala (—1) and Phe (+1), as the nascent chain is transported into the lumen of the endoplasmic reticulum. Proinsulin folds and two disulfide bonds crosslink the ends of the molecule as shown. Before secretion, a trypsinlike enzyme cleaves after a pair of basic residues 31, 32 and 59, 60 then a carboxypeptidase B-like enzyme removes these basic residues to generate the mature form of insulin. 

Next, this RNA is translated into a pre-propeptide, which enters the endoplasmic reticulum (Fig. 1—9). This is the precursor of a precursor, sometimes also called the grandparent of the neuropeptide neurotransmitter. This pre-propeptide grandparent neuropeptide has a peptide tail, called a signal peptide, which allows the pre-propeptide to enter the endoplasmic reticulum, where the tail is clipped off by an enzyme called a signal peptidase with formation of the propeptide, or parent of the neuropeptide. The propeptide is the direct precursor of the neuropeptide neurotransmitter itself. 

Bacterial signal peptidase is an example of a known enzyme that could serve as a target for new antibacterial agents [13], Recently, a catalytically active, soluble fragment of signal peptidase from E. coli has been crystallized as a complex with a P-lactam inhibitor [69], This represents a major step in the efforts toward the rational design of inhibitors that can be readily tested for their enzyme inhibition and bacterial growth-inhibition activities. 

Penicillins have been considered for the inhibition of other bacterial serine enzymes than the DD-peptidases and /3-lactamases. For instance, bacterial signal peptidases (SPases) are essential for cell viability and therefore represent nowadays a class of novel antibacterial target <1998NAT186>. SPases are involved in protein translocation through the cytoplasmic membrane in the final step of the bacterial protein secretion pathway <1997PSC1119>. 5(S)-Stereoisomers of penems have been found to inhibit SPases <1995BML443>. The most potent inhibitors are 5/AV-tricyclic penems <2003S1732>. 

The pharmacological evidence compiled for y-secretase is indicative of the activity of an aspartic protease requiring at least one additional cofactor. The location of the active site within the membrane makes y-secretase quite unique. Currently, there is only one precedent for a similar, tricky enzyme, signal peptidase, which shares several features and most of the problems associated with inner-membrane location [25]. It will not, unfortunately, be easy to isolate and purify the membrane-stabilized protease while retaining its activity. It has, therefore, so far escaped crystallization and X-ray structure determination. Mutation analysis of the two conserved aspartic acids of all presenilins supports their key role in y-secretase... 

The signal peptidases found so far all seem to be integral membrane proteins (Brennan et al., 1980 Lively and Walsh, 1983 Fujimoto et al., 1984 Wolfe et al., 1983b). The amino terminus of the E. coli enzyme appears to be an uncleaved signal peptide (Wolfe and Wickner, 1984). In E. coli the signal peptidase has been reported to reside in approximately equal amounts in both the inner and outer membranes (Mandel... 

The signal sequence is proteoly tically cleaved by signal pepetidase (member enzyme of translocon) once protein is translocated. The eukaryotic signal peptidases have multiple catalytic subunits with broad substrate specificity. The enzyme generally cleaves at a site that has small aliphatic residues at position -1 and -3. On-line prediction of signal peptide and cleavage site is available at PrediSi (http //www.predisi.de). 

---