Roles of the signal peptide and mature domains in the secretion and maturation of the neutral metalloprotease from Streptomyces cacaoi

Cloning, Purification and Characterization of the Collagenase ColA Expressed by Bacillus cereus ATCC 14579

Bacterial collagenases differ considerably in their structure and functions. The collagenases ColH and ColG from Clostridium histolyticum and ColA expressed by Clostridium perfringens are well-characterized collagenases that cleave triple-helical collagen, which were therefore termed as ´true´ collagenases. ColA from Bacillus cereus (B. cereus) has been added to the collection of true collagenases. However, the molecular characteristics of B. cereus ColA are less understood. In this study, we identified ColA as a secreted true collagenase from B. cereus ATCC 14579, which is transcriptionally controlled by the regulon phospholipase C regulator (PlcR). B. cereus ATCC 14579 ColA was cloned to express recombinant wildtype ColA (ColA^wt) and mutated to a proteolytically inactive (ColA^E501A) version. Recombinant ColA^wt was tested for gelatinolytic and collagenolytic activities and ColA^E501A was used for the production of a polyclonal anti-ColA antibody. Comparison of ColA^wt activity with homologous proteases in additional strains of B. cereus sensu lato (B. cereus s.l.) and related clostridial collagenases revealed that B. cereus ATCC 14579 ColA is a highly active peptidolytic and collagenolytic protease. These findings could lead to a deeper insight into the function and mechanism of bacterial collagenases which are used in medical and biotechnological applications.

Expression, purification and functional analysis of an odorant binding protein AaegOBP22 from Aedes aegypti

Mosquitoes that act as disease vectors rely upon olfactory cues for host-seeking, mating, blood feeding and oviposition. To reduce the risk of infection in humans, one of the approaches focuses on mosquitoes' semiochemical system in the effort to disrupt undesirable host-insect interaction. Odorant binding proteins (OBPs) play a key role in mosquitoes' semiochemical system. Here, we report the successful expression, purification of an odorant binding protein AaegOBP22 from Aedes aegypti in heterologous system. Protein purification methods were set up by Strep-Tactin affinity binding and size-exclusion chromatography. Analysis by SDS-PAGE and mass spectrum revealed the protein's purity and molecular weight. Circular dichroism spectra showed the AaegOBP22 secondary structure had a pH dependent conformational change. The protein functions of AaegOBP22 were tested by fluorescent probe 1-NPN binding assays and ligands competitive binding assays. The results show AaegOBP22 proteins have characteristics of selective binding with various ligands.

Extracellular metalloendopeptidase of Streptomyces rimosus

Metalloendopeptidase was isolated from Streptomyces rimosus culture filtrates in a homogeneous form. It was determined to be a 15 kDa basic protein, most active around pH 7.5, and susceptible to inhibition by chelating agents, N-bromosuccinimide, thiorphan, and 10(-4) M zinc. The enzyme was highly specific for phenylalanine at the N-side of endopeptide bonds. Determination of amino acid sequence of the enzyme's NH(2)-part allowed the recognition of its structure homology with isolated and predicted metallopeptidases from several Streptomyces species. The data contribute to the definition of M7 family of metalloendopeptidases in streptomycetes.

Intramolecular chaperones: polypeptide extensions that modulate protein folding

Several prokaryotic and eukaryotic proteins are synthesized as precursors in the form of pre-pro-proteins. While the pre-regions function as signal peptides that are involved in transport, the propeptides can often catalyze correct folding of their associated proteins. Such propeptides have been termed intramolecular chaperones. In cases where propeptides may not directly catalyze the folding reaction, it appears that they can facilitate processes such as structural organization and oligomerization, localization, sorting and modulation of enzymatic activity and stability of proteins. Based on the available literature it appears that propeptides may actually function as 'post-translational modulators' of protein structure and function. Propeptides can be classified into two broad categories: Class I propeptides that function as intramolecular chaperones and directly catalyze the folding reaction; and Class II propeptides that are not directly involved in folding.

N-terminus of mature heat-labile enterotoxin chain B is critical for its extracellular secretion in Vibrio cholerae

The effects of addition of a few amino acids to the amino- and carboxy-terminal regions of the mature portion of the heat-labile enterotoxin chain B (LTB) of Escherichia coli on protein export, secretion and assembly were investigated. In E. coli, LTB (secretory protein) with or without the extension at the N- or C-terminus accumulated in the periplasmic fraction. For Vibrio cholerae, LTB with the extension at the C-terminus was exported to the periplasm followed by secretion to the extracellular milieu. However, LTB with the N-terminus extension was exported to the periplasm only. Our findings suggest that in the case of V. cholerae, the N-terminus of the mature LTB plays an important role in its secretion to the extracellular milieu.

Modifications of Streptomyces signal peptides and their effects on protein production and secretion

As for other organisms, proteins to be secreted in Streptomyces are produced as preproteins consisting of the mature protein preceded by a N-terminal signal peptide which is cleaved off during membrane translocation. Although primary sequences are seldom conserved among signal peptides, they all have a typical tripartite structure: a basic amino-terminus, a central apolar core and a carboxy-terminal region containing the signal peptidase recognition site. In vitro mutagenesis studies have been carried out on various signal peptides to analyse the structure-function relationship of each of the three regions of Streptomyces signal peptides. In the current paper the present knowledge of Streptomyces leader sequences and the impact of introduced mutations on transcription, translation and secretion of homologous and heterologous proteins is reviewed.