Various approaches have been developed to exploit the functional properties of proteins and the structural properties of nanoscale materials. These range from biomolecule-nanomaterial hybrids and biocatalytically-generated self-assembled amphiphiles to protein-based structural templates. In this issue of Biotechnology Journal, Glover et al.  exploit the extremophilic protein γ-prefoldin (γPFD), which spontaneously forms long and straight filaments that are thermally stable to over 80°C and that can be engineered to nucleate platinum into functional nanowires.
Nature's catalytic and biomolecular machinery provides an extraordinary diversity of structure, templates and macromolecular assemblies, all with highly specific function. Three broad paradigms have been employed to generate functional biological-nanomaterial hybrids (Fig. 1). Perhaps the most common approach involves the conjugation of proteins, such as enzymes and antibodies, onto nanomaterials. Examples include surface curvature-stabilized enzymes bound to silica nanoparticles  and carbon nanotubes  for use in sensors , surface-active catalysts , and nanocomposites for antimicrobial paints and coatings [6, 7]. A less common, yet highly powerful, approach is the directed assembly of nanostructures using biocatalysis. One example is the lipase-catalyzed synthesis of trehalose diesters that pack at the molecular dimension, leading to fibrous gels at the macroscopic scale, the latter reflected in biodegradable organogel properties  with potential application in oil spill remediation .
The third approach involves manipulating nature's biomolecules to give protein assemblies with tailored structures and unique molecular templating capabilities. The engineered γ-prefoldin (γPFD) filaments elegantly developed by Clark and co-workers  in the current issue report an exam-ple of the remarkable flexibility of nature to be manipulated and provide templating properties that cannot be emulated through conventional synthetic means. γPFD is an extremely thermostable filamentous protein isolated from the hyperthermophilic archaeon, Methanocaldococcus janashii . Following expression of γPFD in Escherichi coli, the protein is dissolved in 8 M guanidinium-HCl, and then rapidly diluted with aqueous buffer. The resulting γPFD filaments ha a range of average lengths, from 200 to over 800 nm, and optimal stability of ∼85°C, which is consistent with the physiological temperature of M. janaschii.
Glover et al.  attempt to stabilize the γPFD to even higher temperatures to exploit functional advantages, for example, in the nucleation of metals to form metallic nanowires. γPFD consists of coiled-coil sequences in heptad repeat segments  with hydrophobic residues in two of these sequences and packed together to form a nonpolar interface for fibril formation. Glover et al.  hypothesize that additional hydrophobic residues in more polar sequences of the heptad segments would result in increased packing and higher thermostability. To that end, the authors preform site-directed mutagenesis, with three mutants (Y15L, A128I, and T131I) yielding fibrils with stability up to 103°C and increased length over the wild-type γPFD.
These enhanced thermostable mutants serve as excellent templates for the formation of metallic nanowires, where elevated temperatures facilitate metal formation. Incubation of the γPFD mutants with (NH4)2PtCl4 at 100°C results in rapid nucleation and a fibrous web of material. Wild-type γPFD, however, could not form nanowires as a result of filament clumping upon addition of the Pt salt, presumably due to the lower thermostability leading to shorter, unstable filaments. Such an example of manipulating a natural fibrous material may just be the “tip of the iceberg” of opportunities to generate biomolecules with unique structures, tailored stabilities, and a range of applications in sensing, electronic materials, tissue engineering and regenerative medicine, food, and industrial products.