Solubilization of Phospholipid by Surfactin Leading to Lipid Nanodisc and Fibrous Architecture Formation.

Nanodiscs belong to a category of water-soluble lipid bilayer nanoparticles. In vivo nanodisc platforms are useful for studying isolated membrane proteins in their native lipid environment. Thus, the development of a practical method for nanodisc reconstruction has garnered consider-able research interest. This paper reports the self-assembly of a mixture of bio-derived cyclic peptide, surfactin (SF), and l-α-dimyristoylphosphatidylcholine (DMPC). We found that SF induced the solubilization of DMPC multilamellar vesicles to form their nanodiscs, which was confirmed by size-exclusion chromatography, dynamic light scattering, and transmission electron microscopy analyses. Owing to its amphiphilic nature, the self-assembled structure prevents the exposure of the hydrophobic lipid core to aqueous media, thus embedding ubiquinol (CoQ10) as a hydrophobic model compound within the inner region of the nanodiscs. These results highlight the feasibility of preparing nanodiscs without the need for laborious procedures, thereby showcasing their potential to serve as promising carriers for membrane proteins and various organic compounds. Additionally, the regulated self-assembly of the DMPC/SF mixture led to the formation of fibrous architectures. These results show the potential of this mixture to function as a nanoscale membrane surface for investigating molecular recognition events.

pH-induced conformational change of natural cyclic lipopeptide surfactin and the effect on protease activity.

The cyclic lipopeptide surfactin (SF) is one of the promising environmental friendly biosurfactants abundantly produced by microorganisms such as Bacillus subtilis. SF shows excellent surface properties at various pH, together with lower toxicity and higher biodegradability than commonly used petroleum-based surfactants. However, the effect of the dissociation degree of SF on self-assembly is still incompletely understood, even though two acidic amino acid residues (Asp and Glu) are known to influence eventual surface and biological functions. Here, we report changes in the secondary structure of SF induced by increased pH, and the effect on protease activity. We found that the ß-sheet and ß-turn formation of SF are significantly enhanced through increased dissociation of Asp and Glu as revealed by a titration experiment of SF solution to estimate apparent pK1 and pK2 values together with circular dichroism spectroscopy. We also studied the activity of the common detergent enzyme subtilisin in SF solution at above its pK2 (pH 7.6) to understand the role of the dissociation degree in the interaction with the protein. The mixing of SF having a unique cyclic topological feature with subtilisin suppressed the decrease in protease activity observed in the presence of synthetic surfactants such as sodium dodecyl sulfate and polyoxyethylene alkyl ether. Thus, SF has great potential for use in laundry detergent formulations, to improve the stability and reliability of detergent enzymes.

Selective encapsulation of cesium ions using the cyclic peptide moiety of surfactin: Highly efficient removal based on an aqueous giant micellar system.

Cyclic peptide of surfactin (SF) is one of the promising environment-friendly biosurfactants abundantly produced by microorganisms such as Bacillus subtilis. SF is also known to act as an ionophore, wherein alkali metal ions can be trapped in the cyclic peptide. Especially, SF is expected to show high affinity for Cs(+) because of the distinctive cavity size and coordination number. In this study, we reported the specific interaction between SF and Cs(+) and succeeded in the highly efficient removal of Cs(+) from water using giant SF micelles as a natural sorbent. The specific interaction between SF and Cs(+) to form their inclusion complex was revealed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy. We found that SF micelles selectively encapsulate Cs(+), which was suggested by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). A highly effective separation of Cs(+) immobilized on the surface of the SF micelles was also achieved through facile centrifugal ultrafiltration in 91% even in coexisting with other alkali metal ions such as Na(+) and K(+). Thus, the use of the giant micellar system of SF with its high Cs(+) affinity and distinctive assembling properties would be a new approach for the treatment of contaminated soil and water.

A novel potent cell cycle inhibitor dehydrophenylahistin--enzymatic synthesis and inhibitory activity toward sea urchin embryo.

A novel dehydrogenated cyclic dipeptide named as dehydrophenylahistin (deltaPLH) was effectively prepared from a fungal metabolite (-)-phenylahistin by the enzymatic conversion catalyzed by the cell-free extract of Streptomyces albulus KO-23, an albonoursin-producing actinomycete. deltaPLH exhibited more than 1,000 times as high potent inhibitory activity toward the first cleavage of sea urchin embryos as (-)-phenylahisitn which has been reported to be a cell cycle inhibitor and more than 10,000 as high as albonoursin, indicating that deltaPLH is a promising leading compound for anticancer drugs.

Enzymatic synthesis of dehydro cyclo(His-Phe)s, analogs of the potent cell cycle inhibitor, dehydrophenylahistin, and their inhibitory activities toward cell division.

Cyclo(His-Phe) was effectively converted to its dehydro derivatives by the enzyme of Streptomyces albulus KO-23, an albonoursin-producing actinomycete. Two types of dehydro derivatives were isolated from the reaction mixture and identified as cyclo(DeltaHis-DeltaPhe) and cyclo(His-DeltaPhe). This is the first report on cyclo(His-DeltaPhe) and the enzymatic preparation of both compounds. Cyclo(DeltaHis-DeltaPhe), a tetradehydro cyclic dipeptide, exhibited a minimum inhibitory concentration of 0.78 mumol/ml inhibitory activity toward the first cleavage of sea urchin embryos, in contrast to cyclo(His-DeltaPhe) that had no activity. The finding that the isoprenylated derivative of cyclo(DeltaHis-DeltaPhe), dehydrophyenylahistin, had 2,000 times higher activity than cyclo(DeltaHis-DeltaPhe) indicates that an isoprenyl group attached to an imidazole ring of the compound was essential for the inhibitory activity.