Function and Redundancy of the Chaplin Cell Surface Proteins in Aerial Hypha Formation, Rodlet Assembly, and Viability in Streptomyces coelicolor

Abstract

The chaplins are a family of eight secreted proteins that are critical for raising aerial hyphae in Streptomyces coelicolor. These eight chaplins can be separated into two main groups: the long chaplins (ChpA to -C) and the short chaplins (ChpD to -H). The short chaplins can be further subdivided on the basis of their abilities to form intramolecular disulfide bonds: ChpD, -F, -G, and -H contain two Cys residues, while ChpE has none. A "minimal chaplin strain" containing only chpC, chpE, and chpH was constructed and was found to raise a substantial aerial mycelium. This strain was used to examine the roles of specific chaplins. Within this strain, the Cys-containing ChpH was identified as the major polymerization unit contributing to aerial hypha formation and assembly of an intricate rodlet ultrastructure on the aerial surfaces, and the two Cys residues were determined to be critical for its function. ChpC augmented aerial hypha formation and rodlet assembly, likely by anchoring the short chaplins to the cell surface, while ChpE was essential for the viability of wild-type S. coelicolor. Interestingly, the lethal effects of a chpE null mutation could be suppressed by the loss of the other chaplins, the inactivation of the twin arginine translocation (Tat) secretion pathway, or the loss of the rodlins.

Functional Analysis of the Accessory Protein TapA in Bacillus subtilis Amyloid Fiber Assembly

“…Even when not totally blocked, amyloid fiber formation can be severely affected under reducing conditions. This is the case for the chaplin amyloid fibers of Streptomyces coelicolor (17,44). Whether reducing conditions will affect TapA function and whether the cysteines that we removed form disulfide bonds remain to be determined.…”

“…2). Cysteines can have a profound influence on a protein's capacity to form amyloid fibers (17,34). Thus, we investigated how the TapA cysteine residues might contribute to its functionality.…”

“…In the Gram-positive bacterium S. coelicolor, chaplins are the proteins that polymerize into amyloid fibers (5,16). Eight distinct chaplins with high levels of similarity in sequence exist (17). All of them have what is known as the chaplin domain, and only the three long chaplins (ChpA, ChpB, and ChpC) have a C-terminal sorting signal to covalently anchor to cell surfaces via sortase activity.…”

Exploiting amyloid: how and why bacteria use cross-β fibrils

“…The roles of individual chaplins have been addressed at the microbiological level by the construction of a 'minimal strain' and systematic re-introduction of genes. Results indicate that expression of both long and short chaplins, with at least one short chaplin containing the conserved cysteine motif, is vital for the development of a robust aerial mycelium, but that there is otherwise some degree of redundancy among the chaplins [37]. Two recent biophysical studies have shed further light on the role of the chaplins in the formation of the hydrophobic coat [36,38].…”

Dual amyloid domains promote differential functioning of the chaplin proteins duringStreptomycesaerial morphogenesis

“…These proteins work in concert with SapB, a lantibiotic-like peptide (14), during growth in nutrientrich conditions, but when nutrients are limiting, aerial development is exclusively chaplin-dependent (10). With the exception of ChpE, all chaplin domains contain two highly conserved cysteine (Cys) residues that form intramolecular disulfide bonds (15). The chaplins can be divided into two groups: the short chaplins (ChpD-H) and the long chaplins (ChpA-C), where the long chaplins have a C-terminal sorting signal that likely targets them for cell wall attachment.…”