title: Exploring the atomic structure and conformational flexibility of a 320 Å long engineered viral fiber using X-ray crystallography.
abstract: Protein fibers are widespread in nature, but only a limited number of high-resolution structures have been determined experimentally. Unlike globular proteins, fibers are usually recalcitrant to form three-dimensional crystals, preventing single-crystal X-ray diffraction analysis. In the absence of three-dimensional crystals, X-ray fiber diffraction is a powerful tool to determine the internal symmetry of a fiber, but it rarely yields atomic resolution structural information on complex protein fibers. An 85-residue-long minimal coiled-coil repeat unit (MiCRU) was previously identified in the trimeric helical core of tail needle gp26, a fibrous protein emanating from the tail apparatus of the bacteriophage P22 virion. Here, evidence is provided that an MiCRU can be inserted in frame inside the gp26 helical core to generate a rationally extended fiber (gp26-2M) which, like gp26, retains a trimeric quaternary structure in solution. The 2.7 Å resolution crystal structure of this engineered fiber, which measures ∼320 Å in length and is only 20-35 Å wide, was determined. This structure, the longest for a trimeric protein fiber to be determined to such a high resolution, reveals the architecture of 22 consecutive trimerization heptads and provides a framework to decipher the structural determinants for protein fiber assembly, stability and flexibility.
authors: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 233 South 10th Street, Philadelphia, PA 19107, USA.
authors: Anshul
authors: A
authors: Bhardwaj
authors: Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT 84112, USA.
authors: Sherwood R
authors: SR
authors: Casjens
authors: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 233 South 10th Street, Philadelphia, PA 19107, USA.
authors: Gino
authors: G
authors: Cingolani
mesh_terms: D000595:Amino Acid Sequence; D017100:Bacteriophage P22 / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018583:Pliability; D015202:Protein Engineering; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000235:genetics / Q000648:ultrastructure; D017376:Viral Tail Proteins / Q000235:genetics / Q000648:ultrastructure*
chemical_list: D011994:Recombinant Proteins; D017376:Viral Tail Proteins
keywords: bacteriophage P22; protein engineering; protein fiber; tail needle gp26; α-helical coiled coil