Mansoore Hosseini-Koupaei

Bio: Mansoore Hosseini-Koupaei is an academic researcher. The author has contributed to research in topics: Circular dichroism & Quenching (fluorescence). The author has an hindex of 4, co-authored 8 publications receiving 82 citations.

The effect of spermidine on the structure, kinetics and stability of proteinase K: spectroscopic and computational approaches

Abstract: Polyamines (such as spermidine) are low molecular weight compounds which can be used as cosolvents in biological and industrial applications. Cosolvents can interact with proteins and alter their stability and structure. We aimed to study the effect of spermidine (Spd) interaction with proteinase K (PK), with respect to its industrial and biological applications, using different spectroscopic methods of fluorescence, circular dichroism (CD) and UV-visible (UV-vis), as well as simulation methods. Fluorescence quenching data analysis demonstrated that PK had one binding site for Spd. The reduction of Stern–Volmer constant values by increasing the temperature suggested that binding between enzyme and Spd occurred in the ground state (static quenching) and the stability of the complex was decreased at higher temperatures. The values of enthalpy and entropy changes as well as simulation methods illustrated that hydrogen bonds and van der Waals forces played a major role in the PK–Spd complex formation. CD data analysis also showed the decrease in the β-sheet and the increase in the α-helix and β-turn of PK induced by Spd. UV-visible results indicated some alteration in the hydrophobicity of the Trp microenvironment of PK by adding Spd, confirming the intrinsic fluorescence emission results. The kinetic and thermal stability studies showed that Spd could increase the activity and stability of PK, and that this might be due to the changes in the secondary and tertiary structures of the enzyme after Spd modification.

Kosmotropes and chaotropes: modelling preferential exclusion, binding and aggregate stability

Abstract: Kosmotropic cosolvents added to an aqueous solution promote the aggregation of hydrophobic solute particles, while chaotropic cosolvents act to destabilise such aggregates. We discuss the mechanism for these phenomena within an adapted version of the two-state Muller-Lee-Graziano model for water, which provides a complete description of the ternary water/cosolvent/solute system for small solute particles. This model contains the dominant effect of a kosmotropic substance, which is to enhance the formation of water structure. The consequent preferential exclusion both of cosolvent molecules from the solvation shell of hydrophobic particles and of these particles from the solution leads to a stabilisation of aggregates. By contrast, chaotropic substances disrupt the formation of water structure, are themselves preferentially excluded from the solution, and thereby contribute to solvation of hydrophobic particles. We use Monte Carlo simulations to demonstrate at the molecular level the preferential exclusion or binding of cosolvent molecules in the solvation shell of hydrophobic particles, and the consequent enhancement or suppression of aggregate formation. We illustrate the influence of structure-changing cosolvents on effective hydrophobic interactions by modelling qualitatively the kosmotropic effect of sodium chloride and the chaotropic effect of urea.