High-level expression of Bacillus thuringiensis phosphatidylinositol-specific phospholipase C by the Bacillus brevis host-vector system

Transbilayer lipid interactions mediate nanoclustering of lipid-anchored proteins

Understanding how functional lipid domains in live cell membranes are generated has posed a challenge. Here, we show that transbilayer interactions are necessary for the generation of cholesterol-dependent nanoclusters of GPI-anchored proteins mediated by membrane-adjacent dynamic actin filaments. We find that long saturated acyl-chains are required for forming GPI-anchor nanoclusters. Simultaneously, at the inner leaflet, long acyl-chain-containing phosphatidylserine (PS) is necessary for transbilayer coupling. All-atom molecular dynamics simulations of asymmetric multicomponent-membrane bilayers in a mixed phase provide evidence that immobilization of long saturated acyl-chain lipids at either leaflet stabilizes cholesterol-dependent transbilayer interactions forming local domains with characteristics similar to a liquid-ordered (lo) phase. This is verified by experiments wherein immobilization of long acyl-chain lipids at one leaflet effects transbilayer interactions of corresponding lipids at the opposite leaflet. This suggests a general mechanism for the generation and stabilization of nanoscale cholesterol-dependent and actin-mediated lipid clusters in live cell membranes.

How to achieve high-level expression of microbial enzymes: strategies and perspectives

Microbial enzymes have been used in a large number of fields, such as chemical, agricultural and biopharmaceutical industries. The enzyme production rate and yield are the main factors to consider when choosing the appropriate expression system for the production of recombinant proteins. Recombinant enzymes have been expressed in bacteria (e.g., Escherichia coli, Bacillus and lactic acid bacteria), filamentous fungi (e.g., Aspergillus) and yeasts (e.g., Pichia pastoris). The favorable and very advantageous characteristics of these species have resulted in an increasing number of biotechnological applications. Bacterial hosts (e.g., E. coli) can be used to quickly and easily overexpress recombinant enzymes; however, bacterial systems cannot express very large proteins and proteins that require post-translational modifications. The main bacterial expression hosts, with the exception of lactic acid bacteria and filamentous fungi, can produce several toxins which are not compatible with the expression of recombinant enzymes in food and drugs. However, due to the multiplicity of the physiological impacts arising from high-level expression of genes encoding the enzymes and expression hosts, the goal of overproduction can hardly be achieved, and therefore, the yield of recombinant enzymes is limited. In this review, the recent strategies used for the high-level expression of microbial enzymes in the hosts mentioned above are summarized and the prospects are also discussed. We hope this review will contribute to the development of the enzyme-related research field.

Two distinct phosphatidylinositol-specific phospholipase Cs from Streptomyces antibioticus

Two phosphatidylinositol-specific phospholipase C (PI-PLC) genes from Streptomyces antibioticus were cloned by a shotgun method using Streptomyces lividans TK24 as a host. The genes of the two PI-PLCs (named as PLC1 and PLC2) were adjoined and opposite in the direction of transcription/translation. Both of them were confirmed to be expressed in S. antibioticus. The two enzymes were different in the following properties. (i) PLC2 had considerable sequence similarity to other bacterial PI-PLCs, while PLC1 had a short stretch that was similar to PI-PLCs of eukaryotes rather than the other bacterial enzymes. (ii) PLC1 was Ca2+-dependent, whereas PLC2 was not. (iii) PLC1 generated myo-inositol-1-phosphate and myo-inositol-1:2-cyclic phosphate simultaneously from PI, but PLC2 showed sequential formation of them. (iv) PLC2 has GPI-anchor-degrading activity while PLC1 does not have. Both enzymes did not hydrolyze phosphatidylcholine, phosphatidylinositol-4-monophosphate and phosphatidylinositol-4,5-bisphosphate. Both PLC1 and PLC2 contained two histidine residues that might be catalytic residues. PLC1 has residues that possibly form a Ca2+-binding site. Then it was suggested that both PLC1 and PLC2 act according to the catalytic mechanism using the two histidine residues as proposed in both eukaryotic and prokaryotic enzymes, but that PLC1 has a more 'eukaryotic' mechanism in which Ca2+ participates than that of the Ca2+-independent bacterial enzymes. Thus, we propose that PLC2 is a conventional 'bacteria-type' enzyme, while PLC1 is more closely related to the eukaryotic enzymes rather than the bacterial enzymes.

Mutational analysis of the C-terminal signal peptide of bovine liver 5'-nucleotidase for GPI anchoring: a study on the significance of the hydrophilic spacer region

Bovine liver 5'-nucleotidase is a GPI-anchored protein whose Ser523 attaches to GPI as the omega-site. For GPI-modification, pro-protein of the enzyme possesses a signal peptide at the C-terminus, comprising a hydrophilic spacer sequence of 8 amino acid residues and the following hydrophobic region of 17 amino acid residues. The C-terminal signal peptide is replaced by GPI on a luminal leaflet of endoplasmic reticulum. To characterize the C-terminal signal peptide for GPI modification, we constructed a series of deletion and elongation mutant genes, altering length of the hydrophilic spacer sequence by site-directed mutagenesis. Systematic deletion and Ala insertion of the sequence showed that the sequence of 6-14 residues were compatible for GPI modification. For GPI transfer to the pro-protein, the optimum length of spacer sequence would be 8, being consistent with natural selection. The spacer sequence may play a role for leading the omega-residue correctly to the active site of putative GPI transamidase. The elongation of the spacer is more permissible than deletion. Nevertheless, the length of the spacer sequence may influence efficiency of GPI modification by its positive or negative control.