Livia Petrescu

Protein association investigated by THz spectroscopy and molecular modeling

Macromolecular crowding is a common intracellular phenomenon that causes conformational changes of proteins and protein association. We investigated these macromolecular crowding effects on a highly concentrated BSA solution using THz spectroscopy and molecular modeling. We modeled several BSA 50% w/w solutions comprising two BSA molecules in a water box and selected a single model based on the agreement with THz experiments. We further modeled BSA association at concentrations higher than 50% w/w and selected a possible dimer model based on the strength of the interaction between the two proteins. The flexibility of the BSA dimer was compared with the flexibility of BSA from the solution. Monomeric BSA from the solution model presents mobile regions scattered through all the structure, with differences of disposition and extent between the two molecules. Dimerization changes BSA flexibility, as the two molecules from the dimer present compact regions of both high flexibility and low flexibility. The low flexibility regions include their interaction sites.

The flexibility of hydrated bovine serum albumin investigated by THz spectroscopy and molecular modeling

The native cellular environment represents a crowded system comprising high concentrations of soluble molecules that interact mostly in a nonspecific manner. Some of the macromolecular crowding effects occurring in biological media are conformational changes and macromolecular associations. Most of our knowledge on protein folding and protein-protein interactions was acquired from experiments on proteins in dilute solutions or from theoretical models of isolated proteins in either explicit or implicit solvent. Here we present a 50% w/w bovine serum albumin (BSA) solution model that comprises two solute molecules included in a single water box. We determined the vibration spectrum of the 50% w/w BSA solution using THz spectroscopy and we calculated the theoretical THz spectrum. We observed a good correlation between the experimental and theoretical spectra for the frequency range of 0.3 - 1.5 THz. We also investigated the contribution of each BSA molecule to the solution THz spectrum by simulating THz spectra of the two BSA molecules from the solution model and water, each accounting for a 50% w/w BSA solution. The spectra appear to be similar. As the two molecules in our solution model have different conformations, we investigated the importance of the apparently insignificant differences between simulated THz spectra of the two proteins. We found that the differences should be considered significant, as they reflect differences between the flexibility of the two BSA molecules.

Dynamic analysis of the interactions between Si/SiO 2 quantum dots and biomolecules for improving applications based on nano-bio interfaces

Due to their outstanding properties, quantum dots (QDs) received a growing interest in the biomedical field, but it is of major importance to investigate and to understand their interaction with the biomolecules. We examined the stability of silicon QDs and the time evolution of QDs – protein corona formation in various biological media (bovine serum albumin, cell culture medium without or supplemented with 10% fetal bovine serum-FBS). Changes in the secondary structure of BSA were also investigated over time. Hydrodynamic size and zeta potential measurements showed an evolution in time indicating the nanoparticle-protein interaction. The protein corona formation was also dependent on time, albumin adsorption reaching the peak level after 1 hour. The silicon QDs adsorbed an important amount of FBS proteins from the first 5 minutes of incubation that was maintained for the next 8 hours, and diminished afterwards. Under protein-free conditions the QDs induced cell membrane damage in a time-dependent manner, however the presence of serum proteins attenuated their hemolytic activity and maintained the integrity of phosphatidylcholine layer. This study provides useful insights regarding the dynamics of BSA adsorption and interaction of silicon QDs with proteins and lipids, in order to understand the role of QDs biocorona.

Classification based on the anatomo-fractal dimension in biology

The paper is dedicated to the systemic botany domain and analyzes the degree of affinity between the species, genera and families based on fractal theory. The research is conducted on the image information from Gentianaceae family plant, in order to determine their membership to the recognized genera Gentiana, Gentianella and Gentianopsis which were previously tagged into a single genus. Some concepts necessary for defining and quantifying the fractals are introduced, and an algorithm is implemented for calculating the fractal dimension by processing the contours of the organs sections. After the anatomo-fractal analysis, the results of our research propose a correct classification of the Gentiana family into tree genera which confirms the position of the specialists in botanic science.

THz spectroscopy and molecular modeling of bovine serum albumin under various hydration conditions

Bovine serum albumin (BSA) is the most abundant protein in bovine plasma; its three dimensional structure is yet unknown. We investigated the structure and dynamics of BSA in lyophilized samples, in 10% w/w and 50% w/w BSA aqueous solutions using THz spectroscopy and molecular modeling. THz spectra were recorded with a spectral resolution of 7.4 GHz. Theoretical spectra were simulated using a structural model of BSA based on the homology with the known structure of human serum albumin (HSA). The agreement between simulated THz spectra and THz spectra recorded experimentally allowed us to validate the BSA model and the solution models. Based on these models we investigated the flexibility of dry BSA and of BSA with one hydration layer. The hydrated structure of BSA is less flexible than the structure free of water molecules, except for residues 54 - 104 that are more mobile in the hydrated structure. We also investigated the fluctuations of the water molecules within the first hydration layer and identified two groups of water molecules: one that exhibits small fluctuations and one of highly mobile water molecules. These molecules are associated to highly mobile regions from the proteins and move in positive correlation with the neighboring protein regions. We also propose a BSA dimerization model in which the molecules strongly interact. The fluctuations of the BSA monomers and of their first hydration layer were investigated. The two molecules display similar fluctuation patterns, but one of them is slightly more flexible.

Proteins vibrations in THz frequency domain

THz spectroscopy was used to investigate bovine serum albumin (BSA) flexibility in conditions ranging from lyophilised BSA to dilute 10% w/w BSA solution and highly concentrated 50% w/w BSA solutions. The simulated THz spectra of dry and hydrated BSA are in good agreement with the experiments.