Abstract
The modular structure of many protein families, such as β-propeller proteins, strongly implies that duplication played an important role in their evolution, leading to highly symmetrical intermediate forms. Previous attempts to create perfectly symmetrical propeller proteins have failed, however. We have therefore developed a new and rapid computational approach to design such proteins. As a test case, we have created a sixfold symmetrical β-propeller protein and experimentally validated the structure using X-ray crystallography. Each blade consists of 42 residues. Proteins carrying 2-10 identical blades were also expressed and purified. Two or three tandem blades assemble to recreate the highly stable sixfold symmetrical architecture, consistent with the duplication and fusion theory. The other proteins produce different monodisperse complexes, up to 42 blades (180 kDa) in size, which self-assemble according to simple symmetry rules. Our procedure is suitable for creating nano-building blocks from different protein templates of desired symmetry.
Highlights
The modular structure of many protein families, such as β-propeller proteins, strongly implies that duplication played an important role in their evolution, leading to highly symmetrical intermediate forms
Symmetry remains a common feature of proteins [6], many present-day proteins show more limited symmetry than that of the ancestral intermediate forms suggested by the duplication theory of evolution [7,8,9]
Symfoil is an artificial protein with perfect internal threefold symmetry; when a polypeptide carrying 2 repeats instead of 3 repeats was expressed, it assembled into a trimer with two trefoil domains, each with threefold symmetry [2]
Summary
The modular structure of many protein families, such as β-propeller proteins, strongly implies that duplication played an important role in their evolution, leading to highly symmetrical intermediate forms. It is generally accepted that evolution is driven by duplications of genetic material These events allow gene copies to develop independent regulation [1] and to express new proteins that inherit the stable architecture of the parent protein but possess a novel function [2, 3]. Our results provide insight into protein evolution through duplication events, and into methods for creating designer proteins that self-assemble according to simple arithmetical rules. Our novel propeller protein consists of six identical domains known as “blades.” Using a variety of biophysical techniques, we show it to be highly stable and report several high-resolution crystal structures of different forms of the protein. We created polypeptides carrying up to 10 identical blades and showed that these molecules fold to give stable structures
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