2 results
Search Results
Now showing 1 - 2 of 2
Article Citation - WoS: 9Citation - Scopus: 9Ir-Spectroscopic Characterization of an Elongated Ompg Mutant(Elsevier Science inc, 2015) Korkmaz, Filiz; van Pee, Katharina; Yildiz, OezkanOmpG is a nonselective, pH dependent outer membrane protein from Escherichia coli. It consists of 281 residues, forming a 14-stranded beta-sheet structure. In this study, OmpG is extended by 38 amino acids to produce a 16-stranded beta-barrel (OmpG-16S). The resulting protein is investigated by IR-spectroscopy. The secondary structure, pH-dependent opening/closing mechanism, buffer accessibility and thermal stability of OmpG-16S are compared to OmpG-WT. The results show that OmpG-16S is responsive to pH change as indicated by the Amide I band shift upon a switch from acidic to neutral pH. This spectral shift is consistent with that observed in OmpG-WT, which confirms the existence of structural differences consistent with the presence of the open or closed state. Secondary structure analysis after curve-fitting of Amide I band revealed that the additional residues do not fold into beta-sheet; rather they are in the form of turns and unordered structure. In thermal stability experiments, OmpG-16S is found to be as stable as OmpG-WT. Additionally, H/D exchange experiments showed no difference in the exchange rate of OmpG-16S between the acidic and alkaline pH, suggesting that the loop L6 is no longer sufficient to block the pore entrance at acidic pH. (C) 2015 Elsevier Inc. All rights reserved.Article Citation - WoS: 94Citation - Scopus: 99Effect of Progesterone on Dppc Membrane: Evidence for Lateral Phase Separation and Inverse Action in Lipid Dynamics(Elsevier Science inc, 2005) Korkmaz, F; Severcan, FInteractions of progesterone with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) triultilamellar liposomes were investigated as a function of temperature and progesterone concentration by using three non-invasive techniques namely Fourier transform infrared spectroscopy, turbidity at 440 nm, and differential scanning calorimetry. The results reveal that progesterone changes the physical properties of DPPC bilayers by decreasing the main phase-transition temperature, abolishing the pre-transition, broadening the phase-transition profile, disordering the system both in gel and liquid crystalline phase, increasing the dynamics at low concentrations whereas stabilizing the membrane at high concentrations, and inducing phase separation. Progesterone does not change the hydration of the C=O groups, while it strengthens the hydrogen bonding between the PO (2) over bar groups of lipids and the water molecules around. (c) 2005 Elsevier Inc. All rights reserved.
