Membrane transporter dimerization driven by differential lipid solvation energetics of dissociated and associated states

Over two-thirds of integral membrane proteins of known structure assemble into oligomers. Yet, the forces that drive the association of these proteins remain to be delineated, as the lipid bilayer is a solvent environment that is both structurally and chemically complex. In this study we reveal how the lipid solvent defines the dimerization equilibrium of the CLC-ec1 Cl-/H+ antiporter. Integrating experimental and computational approaches, we show that monomers associate to avoid a thinned-membrane defect formed by hydrophobic mismatch at their exposed dimerization interfaces. In this defect, lipids are strongly tilted and less densely packed than in the bulk, with a larger degree of entanglement between opposing leaflets and greater water penetration into the bilayer interior. Dimerization restores the membrane to a near-native state and therefore, appears to be driven by the larger free-energy cost of lipid solvation of the dissociated protomers. Supporting this theory, we demonstrate that addition of short-chain lipids strongly shifts the dimerization equilibrium towards the monomeric state, and show that the cause of this effect is that these lipids preferentially solvate the defect. Importantly, we show that this shift requires only minimal quantities of short-chain lipids, with no measurable impact on either the macroscopic physical state of the membrane or the protein's biological function. Based on these observations, we posit that free-energy differentials for local lipid solvation define membrane-protein association equilibria. With this, we argue that preferential lipid solvation is a plausible cellular mechanism for lipid regulation of oligomerization processes, as it can occur at low concentrations and does not require global changes in membrane properties.

Dimerization of a membrane transporter is driven by differential energetics of lipid solvation of dissociated and associated states

ABSTRACTOver two-thirds of membrane proteins of known structure assemble into oligomers. Yet, the forces that drive the association of these proteins in the membrane remain to be delineated, as the lipid bilayer is a solvent environment that is both structurally and chemically complex. In this study we reveal how the lipid solvent defines the dimerization equilibrium of the CLC-ec1 Cl-/H+ antiporter. Integrating experimental and computational approaches, we show that monomers associate to avoid an energetic penalty for solvating a thinned-membrane defect caused by their exposed dimerization interfaces. Supporting this theory, we demonstrate that this penalty is drastically reduced with minimal amounts of short-chain lipids, which stabilize the monomeric state by preferentially solvating the defect rather than altering the physical state of the membrane. We thus posit that the energy differentials for local lipid-solvation define membrane-protein association equilibria, and describe a molecular-level physical mechanism for lipid regulation of such processes in biological conditions.

Improving the methods of local treatment in case of aphthous lesions on the oral mucosa

Annotation. Contamination of the oral mucosa ulcers with opportunistic microorganisms aggravates the course of chronic recurrent aphthous stomatitis (HRAC). Topical medicines help to eliminate inflammation rapidly and induce fast epithelization of the mucous membrane defect in patients with HRAC. The aim of the work was to create curative composition recipe for the local therapy at HRAC, resulting to higher effectiveness of antimicrobial therapy and acceleration of healing. 43 patients with HRAC were examined. Samples from the lesions were inoculated blood agar and Sabouraud agar. The conventional methods were used for microorganisms’ identification. The sensitivity of isolated strains to antibiotics and antifungals was determined. Antimicrobial activity of the proposed applicative composition was determined by the well method into agar media. It was established that the surface of patients` lesions on the oral mucosa was most often colonized with associations of Streptococci and Neisseriae, Streptococci and C. albicans. For every third patient, the erosive surface was infected with gram-negative microorganisms, including non-ferments and enterobacteria. Most of the isolated bacteria were highly sensitive to antibacterial compounds. Yeast-like fungi exhibited high resistance to fluconazole, itraconazole, 50% of them were resistant to ketoconazole, and resistance to nystatin were revealed in 81% of isolated strains. The proposed application dosage form containing vinyl, decamethoxin, essential oils of carnation and sea buckthorn had a high antimicrobial activity against isolated strains. Obtained results indicate the feasibility of the applicative composition for treatment of erosive and ulcerative lesions, which are caused by microorganisms, in dental practice.

Improving the methods of local treatment in case of aphthous lesions on the oral mucosa

Annotation. Contamination of the oral mucosa ulcers with opportunistic microorganisms aggravates the course of chronic recurrent aphthous stomatitis (HRAC). Topical medicines help to eliminate inflammation rapidly and induce fast epithelization of the mucous membrane defect in patients with HRAC. The aim of the work was to create curative composition recipe for the local therapy at HRAC, resulting to higher effectiveness of antimicrobial therapy and acceleration of healing. 43 patients with HRAC were examined. Samples from the lesions were inoculated blood agar and Sabouraud agar. The conventional methods were used for microorganisms’ identification. The sensitivity of isolated strains to antibiotics and antifungals was determined. Antimicrobial activity of the proposed applicative composition was determined by the well method into agar media. It was established that the surface of patients` lesions on the oral mucosa was most often colonized with associations of Streptococci and Neisseriae, Streptococci and C. albicans. For every third patient, the erosive surface was infected with gram-negative microorganisms, including non-ferments and enterobacteria. Most of the isolated bacteria were highly sensitive to antibacterial compounds. Yeast-like fungi exhibited high resistance to fluconazole, itraconazole, 50% of them were resistant to ketoconazole, and resistance to nystatin were revealed in 81% of isolated strains. The proposed application dosage form containing vinyl, decamethoxin, essential oils of carnation and sea buckthorn had a high antimicrobial activity against isolated strains. Obtained results indicate the feasibility of the applicative composition for treatment of erosive and ulcerative lesions, which are caused by microorganisms, in dental practice.

Clinical features of patients with hemolytic anemia due to red blood cells membrane defect

Background Hemolytic anemia may result from corpuscular orextracorpuscular abnormalities. One of the types of corpuscularabnormalities is membrane defect. The diagnosis is sometimesdifficult and it may need special hematologic investigations. Thereare no data yet on the clinical features of red blood cell membranedefect in Cipto Mangunkusumo Hospital.Objective To evaluate the clinical features and laboratory find-ings of patients with hemolytic anemia due to red blood cells mem-brane defect in Cipto Mangunkusumo Hospital.Methods This was a descriptive study on patients with red bloodcells membrane defect who came to the Thalassemia Center atCipto Mangunkusumo Hospital during 2002-2004.Results In 2002-2004, there were 241 new cases of hemolyticanemia consisted of 116 patients with beta-thalassemia, 109 withHbE-beta thalassemia, 3 with alpha-thalassemia, and 13 with redblood cells membrane defect. The red cells membrane defect pa-tients consisted of 4 males and 9 females, ranging in age from 1months to 14 years. All subjects came to the hospital due to pale-ness as a chief compaint. Hepato-splenomegaly was found in 5 of13 cases. Laboratory findings revealed hemoglobin level 6.4-13.1g/dl (mean 9.4+2.1 g/dl), MCV 58.4-94.5 fl (mean 81.2+10.2 fl),MCHC 31.7-35.8 g/dl (mean 33.9+1.1g/dl), RDW 15.8-28.4%(mean 20.1+3.6%) and normal hemoglobin electrophoresis. Pe-ripheral blood smear showed anisocytosis, poikilocytosis,spherocytes, ovalocytes, stomatocytes, target cells, and fragmentedcells. The most common diagnosis in this group was SoutheastAsian Ovalocytosis (5/13).Conclusions In facing hemolytic anemia with normal Hb electro-phoresis or normal RBC enzyme level, the possibility of red cellsmembrane defect should be taken into consideration as a causeof this disorder. The clinical features and laboratory findings of redblood cells membrane defect patients are highly variable. Occa-sionally, hematologic investigations are necessary