Date Published: April 18, 2017
Publisher: Public Library of Science
Author(s): Sandra Poulos, Sayeh Agah, Nikardi Jallah, Salem Faham, Mark J van Raaij.
The design of proteins that self-assemble into higher order architectures is of great interest due to their potential application in nanotechnology. Specifically, the self-assembly of proteins into ordered lattices is of special interest to the field of structural biology. Here we designed a 2 dimensional (2D) protein lattice using a fusion of a tandem repeat of three TelSAM domains (TTT) to the Ferric uptake regulator (FUR) domain. We determined the structure of the designed (TTT-FUR) fusion protein to 2.3 Å by X-ray crystallographic methods. In agreement with the design, a 2D lattice composed of TelSAM fibers interdigitated by the FUR domain was observed. As expected, the fusion of a tandem repeat of three TelSAM domains formed 21 screw axis, and the self-assembly of the ordered oligomer was under pH control. We demonstrated that the fusion of TTT to a domain having a 2-fold symmetry, such as the FUR domain, can produce an ordered 2D lattice. The TTT-FUR system combines features from the rotational symmetry matching approach with the oligomer driven crystallization method. This TTT-FUR fusion was amenable to X-ray crystallographic methods, and is a promising crystallization chaperone.
Proteins that self-assemble into higher order structures have garnered much interest due to their potential applications in nanotechnology such as sensors [1,2], vaccine development [3,4], diagnostics [5,6], and drug delivery [7,8]. Additionally, self-assembled proteins can be used as scaffolds for templating inorganic materials [9,10,11,12,13,14], which can have a variety of applications in nanoelectronic [15,16,17], plasmonic [18,19,20], magnetic , biomedical [22,23], and catalytic fields [23,24]. Efforts have been directed toward the design of proteins that self-assemble, and various architectures have been pursued such as fibers , nanocages [26,27], and lattices . Engineering proteins into ordered lattices is of special interest to structural biologists in the fields of electron microscopy (EM) and X-ray crystallography.
We achieved many of the desired features of the designed 2D lattice. One important feature is that the fusion of three TelSAM domains achieved not only the desired structure, but also the desired property of pH driven oligomerization. This control over the oligomerization process is likely what allowed us to grow good quality 3D crystals. Previously, successful 2D protein lattice designs were only confirmed by EM [28,29]. Thus, here we demonstrated the first 2D lattice design that produced good quality 3D crystals and allowed the structure to be determined to high resolution by X-ray crystallographic methods. Another critically significant feature that was achieved is that the side by side crystal packing interactions between the TelSAM fibers were entirely mediated by the n-FUR domain. This is essential because it suggests that this design is well suited for further exploration for the crystallization of cargo proteins, with the crystallization contacts already prefabricated.