Behavior of lysozyme adsorbed onto biological liquid crystal lipid monolayer at the air/water interface

The interaction between proteins and lipids is one of the basic problems of modern biochemistry and biophysics.The purpose of this study is to compare the penetration degree of lysozyme into 1,2-diapalmitoyl-sn-glycero-3-phosphocholine(DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethano-lamine(DPPE) by analyzing the data of surface pressure–area(π–A) isotherms and surface pressure–time(π–T) curves.Lysozyme can penetrate into both DPPC and DPPE monolayers because of the increase of surface pressure at an initial pressure of 15 m N/m.However,the changes of DPPE are larger than DPPC,indicating stronger interaction of lysozyme with DPPE than DPPC.The reason may be due to the different head groups and phase state of DPPC and DPPE monolayers at the surface pressure of 15 m N/m.Atomic force microscopy reveals that lysozyme was absorbed by DPPC and DPPE monolayers,which leads to self-aggregation and self-assembly,forming irregular multimers and conical multimeric.Through analysis,we think that the process of polymer formation is similar to the aggregation mechanism of amyloid fibers.     

Solid-state NMR spectroscopy of a membrane protein in biphenyl phospholipid bicelles with the bilayer normal parallel to the magnetic field

Bicelles composed of the long-chain biphenyl phospholipid TBBPC (1-tetradecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-PC) and the short-chain phospholipid DHPC align with their bilayer normals parallel to the direction of the magnetic field. In contrast, in typical bicelles the long-chain phospholipid is DMPC or DPPC, and the bilayers align with their normals perpendicular to the field. Samples of the membrane-bound form of the major coat protein of Pf1 bacteriophage in TBBPC bicelles are stable for several months, align magnetically over a wide range of temperatures, and yield well-resolved solid-state NMR spectra similar to those obtained from samples aligned mechanically on glass plates or in DMPC bicelle samples "flipped" with lanthanide ions so that their bilayer normals are parallel to the field. The order parameter of the TBBPC bicelle sample decreases from approximately 0.9 to 0.8 upon increasing the temperature from 20 degrees C to 60 degrees C. Since the frequency spans of the chemical shift and dipolar coupling interactions are twice as large as those obtained from proteins in DMPC bicelles without lanthanide ions, TBBPC bicelles provide an opportunity for structural studies with higher spectral resolution of the metal-binding membrane proteins without the risk of chemical or spectroscopic interference from the added lanthanide ions. In addition, the large temperature range of these samples is advantageous for the studies of membrane proteins that are unstable at elevated temperatures and for experiments requiring measurements as a function of temperature.     

Covalent binding of ultrasound-treated japonica rice bran protein to catechin: Structural and functional properties of the complex

Due to the existence of many disulfide bonds in japonica rice bran protein (JRBP) molecules, their solubility is poor, which seriously affects other functional properties. To improve the functional characteristics of JRBP molecules, they were processed by ultrasound technology, and JRBP-catechin (CC) covalent complex was prepared. The structural and functional properties of indica and japonica rice bran proteins and their complexes were compared; furthermore, the changes in the structural and functional properties of JRBP-CC under different ultrasound conditions were investigated. The results showed that compared with indica rice bran protein (IRBP), the secondary structure of JRBP-CC was very different, the water holding capacity (WHC) was higher, and the emulsification performance was better. Different ultrasound conditions had different effects on the functional properties of JRBP-CC. When the ultrasound power was 200 W, the λ_max redshift of the JRBP-CC complex was the most significant, the particle size was the smallest, the absolute value of the zeta potential was the largest, and the hydrophobicity and microstructure of the JRBP-CC complex were the best. Concurrently, the maximum WHC and oil holding capacity (OHC) of JRBP-CC under these conditions were 7.54 g/g and 6.87 g/g, respectively. Moreover, the emulsifying activity index (EAI) and emulsifying stability index (ESI) were 210 m²/g and 47.8 min, respectively, and the scavenging activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ABTS⁺ were 71.96 % and 80.07 %, respectively.