Effect of Molecular Dynamics and Internal Water Contact on the Photophysical Properties of Red pH-Sensitive Proteins

The pH dependence of the absorption and (time-resolved) fluorescence of two red-shifted fluorescent proteins, mCardinal and mNeptune, was investigated. Decay-associated spectra were measured following fluorescence excitation at 470 nm in PBS buffer with a pH that ranged from 5.5 to 8.0. The fluorescence of both proteins shows two different decay components. mCardinal exhibits an increase in the long-lived fluorescence component with acidification from 1.34 ns at pH 8.0 to 1.62 ns at pH 5.5. An additional fast decay component with 0.64 ns at pH 8.0 up to 1.1 ns at pH 5.5 was found to be blue-shifted compared to the long-lived component. The fluorescence lifetime of mNeptune is insensitive to pH. DAS of mCardinal were simulated assuming a coupled two-level system to describe the 1S state of the chromophore within two different conformations of the protein. MD simulations were conducted to correlate the experimentally observed pH-induced change in the lifetime in mCardinal with its molecular properties. While the chromophores of both protein variants are stabilized by the same number of hydrogen bonds, it was found that the chromophore in mCardinal exhibits more water contacts compared to mNeptune. In mCardinal, interaction between the chromophore and Glu-145 is reduced as compared to mNeptune, but interaction with Thr-147 which is Ser-147 in mNeptune is stronger in mCardinal. Therefore, the dynamics of the excited-state proton transfer (ESPT) might be different in mCardinal and mNeptune. The pH dependency of ESPT is suggested as a key mechanism for pH sensitivity.

Effects of Letrozole on Trabecular Diameter of Long Bone: Mouse Model

Background: Letrozole, a commonly prescribed Neoadjuvant endocrine therapeutic drug in hormone receptor positive breast cancer females, causes osteoporosis along with several other debilitating effects. The objective of this study was to observe the changes in trabecular diameter of femur of mice after exposure to Letrozole. Materials and Methods: This Laboratory based experimental study was carried out at Pakistan Council of Scientific and Industrial Research Centre (PCSIR) Peshawar and Khyber Medical University (KMU) Peshawar from 1st of June 2018 till 30th of July 2018. Thirty-three female albino mice were divided into control and experimental groups. The experimental group was given Letrozole drug at a dose of 1mg/kg/day for 28 days. Weight of these thirty-three mice was measured before and after administration of the drug. The animals were then sacrificed. Femurs were dissected and processed to find out changes in its gross morphology, weight, and trabecular diameter. Results: The overall weight of mice, weight of femur and its trabecular diameter was greater in control Group as compared to experimental Group. Conclusion: Use of Letrozole can cause significant reduction in trabecular diameter of long bones.