February 2017 Archives


Central challenges in the design of large and dynamic macromolecular assemblies for synthetic biology lie in developing effective methods for testing design strategies and their outcomes, including comprehensive assessments of solution behavior. The authors of this paper created and validated an advanced design of a 600-kDa protein homododecamer that self-assembles into a symmetric tetrahedral cage. The monomeric unit is composed of a trimerizing apex-forming domain genetically linked to an edge-forming dimerizing domain. Enhancing the crystallographic results, high-throughput small-angle x-ray scattering (SAXS) comprehensively contrasted our modifications under diverse solution conditions. To generate a phase diagram associating structure and assembly, we developed force plots that measure dissimilarity among multiple SAXS data sets. These new tools, which provided effective feedback on experimental constructs relative to design, have general applicability in analyzing the solution behavior of heterogeneous nanosystems and have been made available as a web-based application. Specifically, our results probed the influence of solution conditions and symmetry on stability and structural adaptability, identifying the dimeric interface as the weak point in the assembly. Force plots comparing SAXS data sets further reveal more complex and controllable behavior in solution than captured by our crystal structures. These methods for objectively and comprehensively comparing SAXS profiles for systems critically affected by solvent conditions and structural heterogeneity provide an enabling technology for advancing the design and bioengineering of nanoscale biological materials.

Yen-Ting Lai1, Greg L. Hura, Kevin N. Dyer, Henry Y. H. Tang, John A. Tainer and Todd O. Yeates Designing and defining dynamic protein cage nanoassemblies in solution 14 Dec 2016:Vol. 2, no. 12

In this paper, the authors show that CRY1, a protein coding gene that activates circadian gene expression and metabolic states and circadian oscillators, binds directly to the PAS domain core of CLOCK:BMAL1. Precise control of CLOCK:BMAL1 activity by coactivators and repressors establishes the ~24 hr periodicity of gene expression. Integrative modeling and solution X-ray scattering studies (conducted at the SIBYLS beamline 12.3.1) irrefutably position a key loop of the CLOCK PAS-B domain in the secondary pocket of CRY1, analogous to the antenna chromophore-binding pocket of photolyase. This study is significant for understanding the clock mechanism as fundamental for the development and application of therapies for circadian-related disorders.

SAXS_Profile_CLOCK _centered.png

SAXS profile of CRY1:CLOCK:BMAL1 repressive complex.

(A) Scattering traces of CRY1:CLOCK:BMAL1 ternary complex (CCB) at different con- centrations are shown. These scattering plots were merged to generate the dataset as the input for FoXSDock. (B) Guinier analysis of CCB shows little or no aggregation of sample. SAXS-calculated molecular weight of the ternary complex is 113 kDa. (C) Kratky plot shows the CCB complex indicates a folded mass with an elongated shape. (D) PDB of FoXSDock HADDOCK driven model that is among the top 20 nearly degenerate docking structures, χ = 2.74.

Michael AK, Fribourgh L, Chelliah Y, Sandate C, Hura GL, Schneidman-Duhovny, Tripathi SM, Takahashi JS, Partch CL “Formation of a repressive complex in the mammalian circadian clock is mediated by the secondary pocket of CRY1” PNAS 2017 Jan 31, doi:10.1073/pnas.1615310114

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