High-resolution structure of a self-assembly-competent form of a hydrophobic peptide captured in a soluble beta-sheet scaffold.
beta-Rich self-assembly is a major structural class of polypeptides, but still little is known about its atomic structures and biophysical properties. Major impediments for structural and biophysical studies of peptide self-assemblies include their insolubility and heterogeneous composition. We have developed a model system, termed peptide self-assembly mimic (PSAM), based on the single-layer beta-sheet of Borrelia outer surface protein A. PSAM allows for the capture of a defined number of self-assembly-like peptide repeats within a water-soluble protein, making structural and energetic studies possible. In this work, we extend our PSAM approach to a highly hydrophobic peptide sequence. We show that a penta-Ile peptide (Ile(5)), which is insoluble and forms beta-rich self-assemblies in aqueous solution, can be captured within the PSAM scaffold in a form capable of self-assembly. The 1.1-A crystal structure revealed that the Ile(5) stretch forms a highly regular beta-strand within this flat beta-sheet. Self-assembly models built with multiple copies of the crystal structure of the Ile(5) peptide segment showed no steric conflict, indicating that this conformation represents an assembly-competent form. The PSAM retained high conformational stability, suggesting that the flat beta-strand of the Ile(5) stretch primed for self-assembly is a low-energy conformation of the Ile(5) stretch and rationalizing its high propensity for self-assembly. The ability of the PSAM to "solubilize" an otherwise insoluble peptide stretch suggests the potential of the PSAM approach to the characterization of self-assembling peptides.
Makabe
Koki
K
Department of Biochemistry and Molecular Biology, The University of Chicago, 929 E. 57th Street, Chicago, IL 60637, USA.
Biancalana
Matthew
M
Yan
Shude
S
Tereshko
Valentina
V
Gawlak
Grzegorz
G
Miller-Auer
Hélène
H
Meredith
Stephen C
SC
Koide
Shohei
S
D000954:Antigens, Surface / Q000737:chemistry*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D001428:Bacterial Vaccines / Q000737:chemistry*; D001898:Borrelia; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D057927:Hydrophobic and Hydrophilic Interactions; D007532:Isoleucine / Q000737:chemistry*; D008074:Lipoproteins / Q000737:chemistry*; D008722:Methods; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary
D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins; D001428:Bacterial Vaccines; D008074:Lipoproteins; D009842:Oligopeptides; C072045:OspA protein; D007532:Isoleucine