Dynamics of the Lens culinaris agglutinin-lactotransferrin and serotransferrin complexes, followed by fluorescence intensity quenching of fluorescein (FITC) with iodide and temperature

Selective Excitation of the 1Lα State of Tryptophan in Collagen-like Peptides Can Reveal the Formation of a Heterotrimer

Fluorescence emission from tryptophan residues has been often used to probe the protein structure due to its transition dipole moment sensitivity to the local environment. We report the fluorescence study of a collagen-like peptide heterotrimer modified with the tryptophan in the X position (X-Y-Gly) n that shows the diminished fluorescence in a homotrimer versus a heterotrimer when the 1Lα state is selectively excited. This behavior is only observed in folded peptides, below the helix-to-coil transition temperature, and can be explained by long-range interactions between the tryptophans located on different strands within the triple helix, not by the change in the local environment. Our results suggest that tryptophan homotransfer is possible at distances much longer than the R 0 (0.5-0.7 nm) previously estimated. These observations imply that the energy transfer between the 1Lα states of proximal tryptophans can be facilitated by constraining their rotation by the helix and, thus, can be employed as a reporter of heterotrimer formation in biosensors.

A TeZla micromixer for interrogating the early and broad folding landscape of G-quadruplex via multistage velocity descending

Biomacromolecular folding kinetics involves fast folding events and broad timescales. Current techniques face limitations in either the required time resolution or the observation window. In this study, we developed the TeZla micromixer, integrating Tesla and Zigzag microstructures with a multistage velocity descending strategy. TeZla achieves a significant short mixing dead time (40 µs) and a wide time window covering four orders of magnitude (up to 300 ms). Using this unique micromixer, we explored the folding landscape of c-Myc G4 and its noncanonical-G4 derivatives with different loop lengths or G-vacancy sites. Our findings revealed that c-Myc can bypass folding intermediates and directly adopt a G4 structure in the cation-deficient buffer. Moreover, we found that the loop length and specific G-vacancy site could affect the folding pathway and significantly slow down the folding rates. These results were also cross-validated with real-time NMR and circular dichroism. In conclusion, TeZla represents a versatile tool for studying biomolecular folding kinetics, and our findings may ultimately contribute to the design of drugs targeting G4 structures.

A rapid microfluidic mixer for high-viscosity fluids to track ultrafast early folding kinetics of G-quadruplex under molecular crowding conditions

Tracking the folding kinetics of macromolecules under molecular crowding conditions represents a tremendous challenge due to the high viscosity of the solution. In this paper, we report a unique T-type microfluidic mixer with seven consecutive ω-shaped baffles for fast mixing of high-viscosity fluids. Numerical simulations and experimental characterizations proved that the micromixer could achieve a mixing time of 579.4 μs for solutions with viscosities about 33.6 times that of pure water. Over a 1000-fold improvement in mixing dead time was accomplished in comparison to those reported previously. We further used this highly efficient micromixer to track the early folding kinetics of human telomere G-quadruplex under molecular crowding conditions. Results indicated an exponential process in the initial folding phase of G-quadruplex, and the G-quadruplex formed a more compact structure under higher degrees of molecular crowding conditions.

A microsecond microfluidic mixer for characterizing fast biochemical reactions

Analysis of fast biochemical reactions requires rapid mixing of solutions. Micromixers can achieve uniform mixing of solutions in a short time and have been recognized as an attractive tool to analyze fast reactions. However, it is still a challenge to design mixers with simple structure and short dead time. Here, a zigzag turbulent micromixer was developed with a rapid mixing time of 16 μs at sample consumption of 10 μL/s. Numerical simulations and confocal imaging validated this result. Application of the chemiluminescence (CL) reaction demonstrated the use of this mixer in analyzing the kinetic process of the CL reaction. In comparison to the turbulent micromixers reported previously, this zigzag mixer has advantages of short dead time, simple structure and low sample consumption. We anticipate the developed mixer to be a useful tool in studying biochemical kinetics or be integrated to Lab-on-a-chip device as a pretreatment functional unit.

Design and evaluation of a passive alcove-based microfluidic mixer

A novel passive microfluidic silicon mixer has been designed, optimized and fabricated. The architecture of the mixer consists of a simple "T" junction, made up by a 20 microm wide by 82 microm deep channel, followed by three repeats of an alcove, each with a triangular obstruction, arranged in a zigzag fashion. Numerical simulations were employed to optimize the geometry, particularly the dimensions of the alcoves, the relative orientation and the spacing between them, and the degree of intrusion associated with them. The simulation results demonstrate that chaotic flow due to recirculation within the alcoves results in transverse velocity that promotes effective fluid mixing. The microfluidic mixer with the simulation-optimized geometry was fabricated with photolithographic techniques and characterized by optical imaging, fluorescence, and Raman microscope spectroscopy. At a sample flow rate of 20 microL/s, the mixer exhibits a short mixing deadtime of approximately 22 micros and a high mixing efficiency under both low and high viscosity conditions. The alcove-based microfluidic silicon mixer offers unique advantages for its short deadtime and slow sample consumption rate. In addition, it provides a valuable component for laboratory-on-a-chip applications for its ease of development into multiple networks for massively parallel analytical processes.