Surface modification using interfacial assembly of the Streptomyces chaplin proteins

Abstract

The chaplin proteins are instrumental in the formation of reproductive aerial structures by the filamentous bacterium Streptomyces coelicolor. They lower the water surface tension thereby enabling aerial growth. In addition, chaplins provide surface hydrophobicity to the aerial hyphae by assembling on the cell surface into an amphipathic layer of amyloid fibrils. We here show that mixtures of cell wall-extracted chaplins can be used to modify a variety of hydrophilic and hydrophobic surfaces in vitro thereby changing their nature. Assembly on glass leads to a protein coating that makes the surface hydrophobic. Conversely, the assembly of chaplins on hydrophobic surfaces renders them hydrophilic. Furthermore, we show that chaplins can stabilize emulsions of oil into water and have an unprecedented surface activity at high pH. Interestingly, this high surface activity coincides with the interfacial assembly of chaplins into a semi-liquid membrane, as opposed to the rigid membrane formed at neutral pH. This semi-liquid membrane possibly represents a trapped intermediate in the assembly process towards the more rigid amyloidal conformation. Taken together, our data shows that chaplins are suitable candidate proteins for a wide range of biotechnological applications.

Diverse supramolecular structures formed by self‐assembling proteins of the Bacillus subtilis spore coat

“…It is also notable that a number of other biological surface structures are constructed out of thin layers of selfassembling components such as the hydrophobins and chaplins of filamentous fungi and streptomyces (Gebbink et al, 2005) and bacterial S-layers . These proteins also hold promise for biotechnological applications (Hektor and Scholtmeijer, 2005;Ekkers et al, 2014;Sleytr et al, 2014).…”

Morphogenesis of Streptomyces in Submerged Cultures

“…This layer, which apparently forms the same mosaic as that found on aerial spores, renders the surface of spores hydrophobic. Recent evidence indicates that chaplins self-assemble into an asymmetric fibrillar membrane when confronted with a hydrophobichydrophilic interface (Bokhove et al, 2013;Ekkers, Claessen, Galli, & Stamhuis, 2014). The chaplin proteins form the main building blocks of the rodlet layer, by assembling into thin fibrils that are aligned by the rodlin proteins into wild-type rodlets .…”

The Role of Functional Amyloids in Multicellular Growth and Development of Gram-Positive Bacteria

“…However, the long chaplins ChpA-C were not detected, presumably due to their covalent coupling to the peptidoglycan. In vitro experiments using mixtures of monomeric chaplins have demonstrated that these proteins have a strong propensity to self-assemble into an amphipathic membrane when confronted with a hydrophobic-hydrophilic interface [ 15 , 16 ]. The hydrophobic side of this membrane is characterized by small 4–6 nm-wide fibrils that are very similar in appearance to the fibrils that are observed on the surface of spores.…”

“…How can this behavior be explained? The assembly of chaplins into an amphipatic amyloidal membrane may be a two-step process [ 16 ]. Initially, monomers accumulate at the water–air interface, leading to the formation of an intermediate, non-amyloidal membrane with high surface activity.…”

“…At low protein concentrations, the speed of assembly into amyloids may be slower, thereby increasing the time and state of high surface activity. Circumstantial evidence for such an intermediate conformation was obtained when the behavior of chaplins was analyzed at elevated pH levels [ 16 ]. Under these conditions, high surface activity was detected, which was dependent on the presence of chaplins, and which was reversible when the pH was lowered to physiological conditions.…”