Blueprinting extendable nanomaterials with standardized protein blocks

 

Blueprinting extendable nanomaterials with standardized protein blocks

 

A wooden house frame consists of many diferent lumber pieces, but because of the regularity of these building blocks, the structure can be designed using straightforward geometrical principles. The design of multicomponent protein assemblies, in comparison, has been much more complex, largely owing to the irregular shapes of protein structures1 . Here we describe extendable linear, curved and angled protein building blocks, as well as inter-block interactions, that conform to specifed geometric standards; assemblies designed using these blocks inherit their extendability and regular interaction surfaces, enabling them to be expanded or contracted by varying the number of modules, and reinforced with secondary struts. Using X-ray crystallography and electron microscopy, we validate nanomaterial designs ranging from simple polygonal and circular oligomers that can be concentrically nested, up to large polyhedral nanocages and unbounded straight ‘train track’ assemblies with reconfgurable sizes and geometries that can be readily blueprinted. Because of the complexity of protein structures and sequence–structure relationships, it has not previously been possible to build up large protein assemblies by deliberate placement of protein backbones onto a blank three-dimensional canvas; the simplicity and geometric regularity of our design platform now enables construction of protein nanomaterials according to ‘back of an envelope’ architectural blueprints.

·         Fig. 1 |

Overview of THR protein blocks and interaction modules. a, Building a house frame from standardized wooden building blocks. THR internal geometry. Blocks are constructed from idealized straight α-helices with an angle of rotation between adjacent helices of Δθ; the remaining degrees of freedom that contribute to the repeat trajectory are also indicated. c, Changing Δθ (while holding the other parameters constant) specifically changes the curvature of the repeat trajectory. d, Single-chain THR modules. e, THR interaction modules. Image of house frame (a, top) by maxer, Can Stock Photo.

·         Design of twistless helix repeats |

Natural and previously designed proteins exhibit a wide range of helical geometries with local irregularities, kinks and deviations from linearity16 that make it difficult to achieve the properties illustrated in Fig. 1 that enable simple nanomaterial scaling (beyond the one dimension accessed by varying the number of repeats in a repeat protein or coiled coil). To achieve these properties, we designed a series of new building blocks constructed from ideal α-helices with all helical axes aligned. Restricting helical geometry to ideal straight helices with zero helical twist in principle considerably limits what types of structure could be built, but this is more than compensated by the great simplification of downstream material design, as illustrated below.

·         Expandable nanomaterials |

The regularity of our blocks in principle enables scaling the size of nanomaterial designs simply by changing the number of repeats in the constituent THRs without altering any of the inter-block interfaces. How the THRs must be aligned to enable expandability differs for each architecture, as described below.