APS March Meeting 2023, Las Vegas, NV

The following talks were presented at the 2023 APS March Meeting in Las Vegas, March 5 - 10:


Intramolecular Structural Vibrations of Triose Phosphate Isomerase

Presented by: Alex McNulty-Romaguera

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Alex McNulty, Tim LaFave, Xiaotong Zhang, Jason Benedict, A.G. Markelz


It has long been contended that protein conformational access is through thermally populated intramolecular structural vibrations (ISV). The possible optimization of the ISV is particularly intriguing for the ubiquitous “perfect enzyme” triose phosphate isomerase (TIM). TIM is found in the two domains of life: archaea and bacteria. Beyond this, TIM’s structural motif, named the TIM-barrel fold, is present in ~10% of known protein catalyst structures. Raising the question, do the structural dynamics of the TIM-barrel fold provide biochemical advantages? In particular the possible long range dynamical coupling between the dimer interface and the substrate access gating by loop 6. the structural dynamics can be examined by Stationary Sample Anisotropic Terahertz Microspectroscopy (SSATM). TIM SSATM measurements were done on large crystals made using a batch microseeding method. This uses smaller crystals harvested, crushed, and diluted into a crystal slurry. Then a whisker tool picks up microcrystals from the slurry to drop some in the wells to stimulate growth of larger crystals. Crystals are used so the orientation of the molecules is known from the unit cell by having a known crystal facet on the aperture. The unit cell and crystal facets are characterized using X-ray crystallography and face indexing. Modeling can then be used to assign collective displacements to the ISV SSATM spectra. Our early measurements have shown reproducibility of an anisotropic band around 26cm-1 that may be loop 6 motions.
NSF grants DBI 1556359 and MCB 1616529, DOE grant DE-SC0016317  | APS LINK

Multivalued electro optic response in near-field THz polarimetry

Presented by: Tim (TJ) LaFave Jr



Tim (TJ) LaFave Jr and Andrea G. Markelz


A robust calibration method to correct instrumentation artifacts in near-field THz polarimetry is reported. An unexpected nonlinear dependence of the NIR quarter waveplate angle with respect to each NIR half waveplate angle was observed in one of two balanced response curves using a time-domain spectroscopy configuration. Signal degradation stems from this multivalued electro-optic response and is associated with an unwanted frequency dependence. Our calibration method removes these artifacts from ZnTe absorbance spectra by normalizing all E-field measurements at every THz polarization angle across the bandwidth of interest (~0.5 – 100 cm-1) and sampling the ZnTe region from which sample measurements are subsequently made. Remaining THz polarization dependencies are additionally removed by normalizing absorbance spectra with respect to the E-field maximum of the reference THz angle spectrum. Reproducible absorbance results were obtained on several triose phosphate isomerase (TPI or TIM) protein crystals with several apertures to sample different regions of the ZnTe crystal. Serendipitously, this method also corrects for previously reported deleterious effects due to defect nonuniformities in ZnTe electro-optic crystals commonly used in near-field polarimetry.
NIH STTR R41 GM140587-01A1  |  APS LINK

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