ORCID Profile
0000-0001-9380-7126
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Publisher: American Chemical Society (ACS)
Date: 20-04-2009
DOI: 10.1021/AR800266R
Abstract: Thermodynamic and kinetic understanding of structural transformations in proteins is critical to new developments in medicine and biotechnology. These fields often require the design of mechanism-based modulators of protein function. Researchers increasingly consider these structural changes-such as folding/unfolding or shuttling between active and inactive states-within the energy landscape concept that supposes a high-dimensional, rugged conformational surface. The unevenness, or asperity, of this conformational surface results from energetic barriers and kinetic traps. However, for a large number of protein reactions, such as reversible folding/unfolding, the literature only reports simple two-state transitions, which calls into question the use of a more complex energy landscape model. The question is: are these reactions really that simple, or are we misled by a biased experimental approach? In this Account, we argue in favor of the latter possibility. Indeed, the frequently employed temperature-jump method only allows recording protein structure changes in the heating direction. Under those conditions, it might not be possible to detect other kinetic pathways that could have been taken in the cooling direction. Recently, however, we have developed bidirectional pressure- and temperature-jump methods, which can offer new insights. Here, we show the potential of these methods both for studying protein folding/unfolding reactions, taking ribonuclease A as model, and for studying functionally relevant protein conformational changes, using the open/closed allosteric transition of tryptophan synthase. For ex le, the heating and cooling temperature-jump induced kinetics involved in the folding/unfolding conformational surface of ribonuclease A is illustrated above. In both of our model systems, the kinetic transition states of several reaction steps were path-dependent, i.e. the rates and thermodynamic activation parameters depend on the direction of the applied pressure and temperature perturbation. This asymmetry suggests that proteins cope with external stress by adapting their structure to form different ensembles of conformational substates. These states are distinguished by their activation enthalpy and entropy barriers, which can be strongly negative in the folding direction. Based on our analysis of activation compressibility and heat capacity, hydration and packing defects of the kinetic transition states are also very important for determining the reaction path. We expect that a more generalized use of this experimental approach should allow researchers to obtain greater insight into the mechanisms of physiologically relevant protein structural changes.
Publisher: Elsevier BV
Date: 03-2006
DOI: 10.1016/J.BBAPAP.2006.01.002
Abstract: Pressure-jump induced relaxation kinetics can be used to study both protein unfolding and refolding. These processes can be initiated by upward and downward pressure-jumps of litudes of a few 10 to 100 MPa, with a dead-time on the order of milliseconds. In many cases, the relaxation times can be easily determined when the pressure cell is connected to a spectroscopic detection device, such as a spectrofluorimeter. Adiabatic heating or cooling can be limited by small pressure-jump litudes and a special design of the s le cell. Here, we discuss the application of this method to four proteins: 33-kDa and 23-kDa proteins from photo-system II, a variant of the green fluorescent protein, and a fluorescent variant of ribonuclease A. The thermodynamically predicted equivalency of upward and downward pressure-jump induced protein relaxation kinetics for typical two-state folders was observed for the 33-kDa protein, only. In contrast, the three other proteins showed significantly different kinetics for pressure-jumps in opposite directions. These results cannot be explained by sequential reaction schemes. Instead, they are in line with a more complex free energy landscape involving multiple pathways.
Publisher: American Meteorological Society
Date: 07-2021
Abstract: The intensity of deep convective storms is driven in part by the strength of their updrafts and cold pools. In spite of the importance of these storm features, they can be poorly represented within numerical models. This has been attributed to model parameterizations, grid resolution, and the lack of appropriate observations with which to evaluate such simulations. The overarching goal of the Colorado State University Convective CLoud Outflows and UpDrafts Experiment (C 3 LOUD-Ex) was to enhance our understanding of deep convective storm processes and their representation within numerical models. To address this goal, a field c aign was conducted during July 2016 and May–June 2017 over northeastern Colorado, southeastern Wyoming, and southwestern Nebraska. Pivotal to the experiment was a novel “Flying Curtain” strategy designed around simultaneously employing a fleet of uncrewed aerial systems (UAS or drones), high-frequency radiosonde launches, and surface observations to obtain detailed measurements of the spatial and temporal heterogeneities of cold pools. Updraft velocities were observed using targeted radiosondes and radars. Extensive datasets were successfully collected for 16 cold pool–focused and seven updraft-focused case studies. The updraft characteristics for all seven supercell updraft cases are compared and provide a useful database for model evaluation. An overview of the 16 cold pools’ characteristics is presented, and an in-depth analysis of one of the cold pool cases suggests that spatial variations in cold pool properties occur on spatial scales from O (100) m through to O (1) km. Processes responsible for the cold pool observations are explored and support recent high-resolution modeling results.
No related grants have been discovered for Jungmin Park.