Search for: All records

Abstract A fragment‐based approach has proven successful in drug design and protein assemblies, yet its potential for constructing biomaterials from simple organic building blocks remains underexplored, particularly for self‐assembly in aqueous phases, where water disrupts intermolecular hydrogen bonding. To the best of our knowledge, this study introduces the first case of integrating fragments from self‐assembling molecules to design a small organic molecule that forms novel hierarchical nanotubes with polymorphism. The molecule's compact design incorporates three structural motifs derived from known nanotube assemblies, enabling a hierarchical assembly process: individual molecules with two conformations form dimers, which organize into hexameric units. These hexamers further assemble into nanotubes comprising 2‐, 5‐, and 6‐protofilament fibers. The nanofibers share a nearly identical asymmetric unit – a hexameric triangular plate – with similar axial and lateral interfaces. The lateral interface, involving interactions between phosphate groups and aromatic rings, exhibits plasticity, allowing slight rotational variations between adjacent units. This adaptability facilitates the formation of diverse nanofiber architectures, showcasing the flexibility of these systems in aqueous environments. By leveraging fragments of self‐assembling molecules, this work demonstrates a straightforward strategy that combines conformational flexibility and self‐assembling fragments to construct advanced supramolecular biomaterials from small organic building blocks in aqueous settings. 

Cannulae are structurally rigid tubular protein filaments that accumulate on the extracellular surface of archaea within the family Pyrodictiaceae during cell growth. These obligate anaerobes propagate under hyperthermophilic conditions in which cannulae form a biomatrix that interconnects and sustains cells. The persistence of cannulae in this environment suggests that these filaments display significant thermostability, which has attracted technological interest in their development as synthetic protein-based biomaterials. Here, we report cryoEM structural analyses of ex vivo and in vitro assembled recombinant cannulae. We demonstrate that the interactions between protomers in native and recombinant cannulae is based on donor strand complementation (DSC), a form of non-covalent polymerization previously observed for bacterial chaperone-usher pili. Unexpectedly, calcium ion coordination at the subunit interfaces reinforces the network of donor strand interactions in the cannulae. This study provides insight into the mechanism of assembly of cannulae and the structural origin of their high stability and rigidity. 

Nucleoside triphosphate (NTP)-dependent protein assemblies such as microtubules and actin filaments have inspired the development of diverse chemically fueled molecular machines and active materials but their functional sophistication has yet to be matched by design. Given this challenge, we asked whether it is possible to transform a natural adenosine 5′-triphosphate (ATP)-dependent enzyme into a dissipative self-assembling system, thereby altering the structural and functional mode in which chemical energy is used. Here we report that FtsH (filamentous temperature-sensitive protease H), a hexameric ATPase involved in membrane protein degradation, can be readily engineered to form one-dimensional helical nanotubes. FtsH nanotubes require constant energy input to maintain their integrity and degrade over time with the concomitant hydrolysis of ATP, analogous to natural NTP-dependent cytoskeletal assemblies. Yet, in contrast to natural dissipative systems, ATP hydrolysis is catalyzed by free FtsH protomers and FtsH nanotubes serve to conserve ATP, leading to transient assemblies whose lifetimes can be tuned from days to minutes through the inclusion of external ATPases in solution. 

Abstract Acinetobacters pose a significant threat to human health, especially those with weakened immune systems. Type IV pili of acinetobacters play crucial roles in virulence and antibiotic resistance. Single-stranded RNA bacteriophages target the bacterial retractile pili, including type IV. Our study delves into the interaction betweenAcinetobacterphage AP205 and type IV pili. Using cryo-electron microscopy, we solve structures of the AP205 virion with an asymmetric dimer of maturation proteins, the nativeAcinetobactertype IV pili bearing a distinct post-translational pilin cleavage, and the pili-bound AP205 showing its maturation proteins adapted to pilin modifications, allowing each phage to bind to one or two pili. Leveraging these results, we develop a 20-kilodalton AP205-derived protein scaffold targeting type IV pili in situ, with potential for research and diagnostics. 

Abstract A contractile sheath and rigid tube assembly is a widespread apparatus used by bacteriophages, tailocins, and the bacterial type VI secretion system to penetrate cell membranes. In this mechanism, contraction of an external sheath powers the motion of an inner tube through the membrane. The structure, energetics, and mechanism of the machinery imply rigidity and straightness. The contractile tail ofAgrobacterium tumefaciensbacteriophage Milano is flexible and bent to varying degrees, which sets it apart from other contractile tail-like systems. Here, we report structures of the Milano tail including the sheath-tube complex, baseplate, and putative receptor-binding proteins. The flexible-to-rigid transformation of the Milano tail upon contraction can be explained by unique electrostatic properties of the tail tube and sheath. All components of the Milano tail, including sheath subunits, are crosslinked by disulfides, some of which must be reduced for contraction to occur. The putative receptor-binding complex of Milano contains a tailspike, a tail fiber, and at least two small proteins that form a garland around the distal ends of the tailspikes and tail fibers. Despite being flagellotropic, Milano lacks thread-like tail filaments that can wrap around the flagellum, and is thus likely to employ a different binding mechanism. 

We investigate the relationship between sequence and supramolecular structure for a pair of bola-amphiphilic peptides, Ac-KLIIIK-NH₂and Ac-KIIILK-NH₂, that self-assemble into supramolecular hydrogels based on cross-b amyloid fibrils.