The ultrafast spectroscopic techniques that we have developed and applied to a variety of important, clinically-relevant biological systems afford a prerogative opportunity to quantitatively explore the intricate and fundamental connection between structural dynamics and biological function at the molecular level, with great application potentials for the fields transcending chemistry, physics, biology, nanomaterial, bioengineering, and medicinal research. We aim to tackle the subtle yet significant issue of bridging the transition from ultrafast conformational fluctuations to structural intermediates that impact or further guide the system evolution, eventually leading to fascinating macroscopic functions. In other words, only the visualization and a deep understanding of the complex biomolecular systems in action can ensure a successful establishment of connections between the fundamental molecular mechanism and biological functions in cells and organisms.
A common thread of my research concerns excited states: they can be vibrationally excited to act as a sensitive probe of local microenvironments, since the vibrational coupling and relaxation report on the geometric constraints and energy transfer events between molecular entities; or they can be electronically excited to expose the detailed structural evolution of photoexcited molecules or photoactive molecular machineries along multidimensional chemical reaction coordinates leading to diverse and unique biological functions in condensed phase.
A successful approach to time-resolve the conformational changes/motions of biomolecular complexes on their intrinsic timescale, either at equilibrium states by thermal motions or at non-equilibrium states by external perturbations (e.g. temperature jump, photoexcitation), would have far-reaching consequences for the fields of protein function prediction, bioengineering, cell biology, cancer treatment, drug design and much more. The techniques that can judiciously accomplish these challenging goals should be able to provide high-resolution multidimensional structural information on the critical timescale of molecular vibrations (being a super-sensitive structural probe), which commonly ranges from 10 femtoseconds to 1 picosecond. That is exactly the essence and unique advantage of the state-of-the-art ultrafast vibrational spectroscopy such as FSRS (Femtosecond Stimulated Raman Spectroscopy) and 2D IR (Two-Dimensional Infra-Red Spectroscopy, see my early works with the late Prof. Robin Hochstrasser).
A natural start for dynamic interrogations on biomolecules concerns proteins, the ubiquitous player in virtually every cellular process: enzyme catalysis, cell signaling, immune responses, cell adhesion, viral infection, etc. Proteins are naturally tuned for function, not for stability. So the time-resolved non-averaged structural studies of proteins even at equilibrium will yield a rich matrix of unprecedented information venturing into new vistas to be explored, from their intrinsic conformational dynamics to interactions with neighboring molecular entities. The prominent research projects to be carried out in my lab will concern photoswitchable fluorescent proteins and membrane integrins. They have enjoyed growing interests in their respective fields due to their unique usage and function in bioimaging and cellular signaling pathways, respectively. But there lies the difficulty to fully characterize their functions and potentials using conventional structural methods. So our approach here sets the goal of (1) revealing the dynamic chromophore-protein interaction to “reversibly” favor and generate specific protonation states of the embedded chromophore in photoactivatable proteins, hence facilitating the targeted design of photoswitchable proteins for real-time live-cell imaging; (2) studying the activation mechanism of membrane integrins, focusing on the lateral transmembrane helix associations and the allosteric conformational changes at the ligand binding site, hence shedding light on various cellular signaling pathways and therapeutic potentials.
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