No abstract

We report two-dimensional (2D) photonic crystal (PC) sensing materials that selectively detect Candida albicans (C. albicans). These sensors utilize Concanavalin A (Con A) protein hydrogels with a 2D PC embedded on the Con A protein hydrogel surface, that multivalently and selectively bind to mannan on the C. albicans cell surface to form crosslinks. The resulting crosslinks shrink the Con A protein hydrogel, reduce the 2D PC particle spacing, and blue-shift the light diffracted from the PC. The diffraction shifts can be visually monitored, measured with a spectrometer, or determined from the Debye diffraction ring diameter. Our unoptimized hydrogel sensor has a detection limit of around 32 CFU/mL for C. albicans. This sensor distinguishes between C. albicans and those microbes devoid of cell-surface mannan such as the gram-negative bacterium E. coli. This sensor provides a proof-of-concept for utilizing recognition between lectins and microbial cell surface carbohydrates to detect microorganisms in aqueous environments.

During prophase I of meiosis, chromosomes become organized as loop arrays around the proteinaceous chromosome axis. As homologous chromosomes physically pair and recombine, the chromosome axis is integrated into the tripartite synaptonemal complex (SC) as this structure’s lateral elements (LEs). While the components of the mammalian chromosome axis/LE—including meiosis-specific cohesin complexes, the axial element proteins SYCP3 and SYCP2, and the HORMA domain proteins HORMAD1 and HORMAD2—are known, the molecular organization of these components within the axis is poorly understood. Here, using expansion microscopy coupled with 2-color stochastic optical reconstruction microscopy (STORM) imaging (ExSTORM), we address these issues in mouse spermatocytes at a resolution of 10 to 20 nm. Our data show that SYCP3 and the SYCP2 C terminus, which are known to form filaments in vitro, form a compact core around which cohesin complexes, HORMADs, and the N terminus of SYCP2 are arrayed. Overall, our study provides a detailed structural view of the meiotic chromosome axis, a key organizational and regulatory component of meiotic chromosomes.

Bovine and human serum albumin (BSA and HSA) are globular proteins that function as bloodstream carriers of hydrophobes such as fatty acids and drugs. We fabricated novel photonic crystal protein hydrogels by attaching 2D colloidal arrays onto pure BSA and HSA hydrogels. The wavelengths of the diffracted light sensitively report on the protein hydrogel surface area. The binding of charged species to the protein hydrogel gives rise to Donnan potentials that change the hydrogel volume causing shifts in the diffraction. These photonic crystal protein hydrogels act as sensitive Coulometers that monitor the hydrogel charge state. We find multiple high-affinity BSA and HSA binding sites for salicylate, ibuprofen and picosulfate by using these sensors to monitor binding of charged drugs. We demonstrate proof-of-concept for utilizing protein hydrogel sensors to monitor protein-ionic species binding.

Understanding the structure of polyglutamine (polyQ) amyloid-like fibril aggregates is crucial to gaining insights into the etiology of at least ten neurodegenerative disorders, including Huntington's disease. Here, we determine the structure of D2Q10K2 (Q10) fibrils using ultraviolet resonance Raman (UVRR) spectroscopy and molecular dynamics (MD). Using UVRR, we determine the fibril peptide backbone Ψ and glutamine (Gln) side chain χ3 dihedral angles. We find that most of the fibril peptide bonds adopt antiparallel β-sheet conformations; however, a small population of peptide bonds exist in parallel β-sheet structures. Using MD, we simulate three different potential fibril structural models that consist of either β-strands or β-hairpins. Comparing the experimentally measured Ψ and χ3 angle distributions to those obtained from the MD simulated models, we conclude that the basic structural motif of Q10 fibrils is an extended β-strand structure. Importantly, we determine from our MD simulations that Q10 fibril antiparallel β-sheets are thermodynamically more stable than parallel β-sheets. This accounts for why polyQ fibrils preferentially adopt antiparallel β-sheet conformations instead of in-register parallel β-sheets like most amyloidogenic peptides. In addition, we directly determine, for the first time, the structures of Gln side chains. Our structural data give new insights into the role that the Gln side chains play in the stabilization of polyQ fibrils. Finally, our work demonstrates the synergistic power and utility of combining UVRR measurements and MD modeling to determine the structure of amyloid-like fibrils.