Interaction of alcohols with serum LDL

Structural properties of an engineered outer membrane protein G mutant, OmpG-16SL, investigated with infrared spectroscopy

The structural and functional differences between wild type (WT) outer membrane protein G and its two mutants are investigated with Fourier transform infrared spectroscopy. Both mutants have a long extension to the primary sequence to increase the number of β-strands from 14 (wild type) to 16 in an attempt to enlarge the pore diameter. The comparison among proteins is made in terms of pH-dependent conformational changes and thermal stability. Results show that all proteins respond to pH change but at different degrees. At acidic environment, all proteins contain the same number of residues participated in β-sheet structure. However, at neutral pH, the mutants have less ordered structure compared to WT porin. Thermal stability tests show that mutants differ significantly from WT porin at neutral pH. Although the transition temperature is directly proportional with the amount of β-sheet content, the changes in the pre-transition phase that pave the way to structural breakdown are shown to involve interactions among charged residues by two-dimensional correlation spectroscopy analysis. Results of the analysis show that side chain interactions play an active role under increasing temperature. Both mutants have more unordered secondary structure but they respond to pH change in tertiary structure level. Findings of this study provided deeper insight on the active players in structural stability of the WT porin.Communicated by Ramaswamy H. Sarma [Formula: see text].

Two-dimensional infrared correlation spectroscopy study of the interaction of oxidized and reduced cytochrome c with phospholipid model membranes

We have used two-dimensional infrared correlation spectroscopy (2D-IR) to study the interaction and conformation of cytochrome c in the presence of a binary phospholipid mixture composed of a zwitterionic perdeuterated phospholipid and a negatively-charged one. The influence of the main temperature phase transition of the phospholipid model membranes on the conformation of cytochrome c has been evaluated by monitoring both the Amide I' band of the protein and the CH(2) and CD(2) stretching bands of the phospholipids. Synchronous 2D-IR analysis has been used to determine the different secondary structure components of cytochrome c which are involved in the specific interaction with the phospholipids, revealing the existence of a specific interaction between the protein with cardiolipin-containing vesicles but not with phosphatidic acid-containing ones. Interestingly, 2D-IR is capable of showing the existence of significant changes in the protein conformation at the same time that the phospholipid transition occurs. In summary, 2D-IR revealed an important effect of the phospholipid phase transition of cardiolipin on the secondary structure of oxidized cytochrome c but not to either reduced cytochrome c or in the presence of phosphatidic acid, demonstrating the existence of specific intermolecular interactions between cardiolipin and cytochrome c.