Lipid intermolecular hydrogen bonding: influence on structural organization and membrane function

The great variety of different lipids in membranes, with modifications to the hydrocarbon chains, polar groups and backbone structure suggests that many of these lipids may have unique roles in membrane structure and function. Acidic groups on lipids are clearly important, since they allow interaction with basic groups on proteins and with divalent cations. Another important property of certain lipids is their ability to interact intermolecularly with other lipids via hydrogen bonds. This interaction occurs through acidic and basic moieties in the polar head groups of phospholipids, and the amide moiety and hydroxyl groups on the acyl chain, sphingosine base and sugar groups of sphingo- and glycolipids. The putative ability of different classes of lipids to interact by intermolecular hydrogen bonding, the molecular groups which may participate and the effect of these interactions on some of their physical properties are summarized in Table IX. It is frequently questioned whether intermolecular hydrogen bonding could occur between lipids in the presence of water. Correlations of their properties with their molecular structures, however, suggest that it can. Participation in intermolecular hydrogen bonding increases the lipid phase transition temperature by approx. 8-16 Cdeg relative to the electrostatically shielded state and by 20-30 Cdeg relative to the repulsively charged state, while having variable effects on the enthalpy. It increases the packing density in monolayers, possibly also in the liquid-crystalline phase in bilayers, and decreases the lipid hydration. These effects can probably be accounted for by transient, fluctuating hydrogen bonds involving only a small percentage of the lipid at any one time. Thus, rotational and lateral diffusion of the lipids may take place but at a slower rate, and the lateral expansion is limited. Intermolecular hydrogen bonding between lipids in bilayers may be significantly stabilized, despite the presence of water, by the fact that the lipids are already intermolecularly associated as a result of the hydrophobic effect and the Van der Waals' interactions between their chains. The tendency of certain lipids to self-associate, their asymmetric distribution in SUVs, their preferential association with cholesterol in non-cocrystallizing mixtures, their temperature-induced transitions to the hexagonal phase and their inhibitory effect on penetration of hydrophobic residues of proteins partway into the bilayer can all be explained by their participation in intermolecular hydrogen bonding interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Myelin basic protein: a multifunctional protein

Myelin basic protein (MBP), the second most abundant protein in central nervous system myelin, is responsible for adhesion of the cytosolic surfaces of multilayered compact myelin. A member of the 'intrinsically disordered' or conformationally adaptable protein family, it also appears to have several other functions. It can interact with a number of polyanionic proteins including actin, tubulin, Ca(2+)-calmodulin, and clathrin, and negatively charged lipids, and acquires structure on binding to them. It may act as a membrane actin-binding protein, which might allow it to participate in transmission of extracellular signals to the cytoskeleton in oligodendrocytes and tight junctions in myelin. Some size isoforms of MBP are transported into the nucleus and thus they may also bind polynucleotides. Extracellular signals received by myelin or cultured oligodendrocytes cause changes in phosphorylation of MBP, suggesting that MBP is also involved in signaling. Further study of this very abundant protein will reveal how it is utilized by the oligodendrocyte and myelin for different purposes.

Intermolecular hydrogen bonding between lipids: influence on organization and function of lipids in membranes

Biological membranes have unique lipid compositions suggesting a specific role for many lipids. Evidence is reviewed concerning the intermolecular forces between glycero- and sphingolipids and cholesterol, the dependence of many of these interactions on the state of ionization of lipids, pH, ionic strength, and divalent cation concentration. The effect of intermolecular interactions between certain lipids on lipid clustering, interaction with cholesterol, on the conformation of proteins, and on transitions to the hexagonal phase is considered. Other forces which cause lipids phase separation or clustering are discussed. It is concluded that lipids are in dynamic equilibrium with their environment and can act as receptors for certain intra- or extra-cellular stimuli, which they can translate into a response by undergoing changes in fluidity, phase transitions, or phase separation.

Acute wake-promoting actions of JNJ-5207852, a novel, diamine-based H3 antagonist

1 1-[4-(3-piperidin-1-yl-propoxy)-benzyl]-piperidine (JNJ-5207852) is a novel, non-imidazole histamine H3 receptor antagonist, with high affinity at the rat (pKi=8.9) and human (pKi=9.24) H3 receptor. JNJ-5207852 is selective for the H3 receptor, with negligible binding to other receptors, transporters and ion channels at 1 microm. 2 JNJ-5207852 readily penetrates the brain tissue after subcutaneous (s.c.) administration, as determined by ex vivo autoradiography (ED50 of 0.13 mg kg(-1) in mice). In vitro autoradiography with 3H-JNJ-5207852 in mouse brain slices shows a binding pattern identical to that of 3H-R-alpha-methylhistamine, with high specific binding in the cortex, striatum and hypothalamus. No specific binding of 3H-JNJ-5207852 was observed in brains of H3 receptor knockout mice. 3 In mice and rats, JNJ-5207852 (1-10 mg kg(-1) s.c.) increases time spent awake and decreases REM sleep and slow-wave sleep, but fails to have an effect on wakefulness or sleep in H3 receptor knockout mice. No rebound hypersomnolence, as measured by slow-wave delta power, is observed. The wake-promoting effects of this H3 receptor antagonist are not associated with hypermotility. 4 A 4-week daily treatment of mice with JNJ-5207852 (10 mg kg(-1) i.p.) did not lead to a change in body weight, possibly due to the compound being a neutral antagonist at the H3 receptor. 5 JNJ-5207852 is extensively absorbed after oral administration and reaches high brain levels. 6 The data indicate that JNJ-5207852 is a novel, potent and selective H3 antagonist with good in vitro and in vivo efficacy, and confirm the wake-promoting effects of H3 receptor antagonists.

Lipid phase separation induced by a hydrophobic protein in phosphatidylserine--phosphatidylcholine vesicles

Differential scanning calorimetry (DSC) was used to detect phase separation induced by hydrophobic myelin protein, lipophilin, in a mixture of phosphatidylserine (PS) and dipalmitoylphosphatidylcholine (DPPC). Preferential binding of PS to the boundary layer of lipophilin causes a decrease in the PS content of the remaining lamellar phase with a resultant shift in the phase-transition temperature to a higher temperature. The phase diagram for this mixture in the presence and absence of lipophilin is presented. From the phase diagram, it can be estimated that for an equimolar mixture of PS and DPPC, the boundary layer contains only PS, although for higher DPPC contents, some DPPC can also be found in the boundary layer. In the case where partial phase separation in induced in this mixture by Ca2+ alone, lipophilin increases the phase separation indicating that it also binds PS preferentially in the presence of Ca2+. Preferential binding of two other acidic lipids, phosphatidic acid and phosphatidyl-glycerol, to the boundary layer was also found, including a mixture where the acidic lipid was the higher melting component in the mixture.

Phase transitions and fatty acid spin label behavior in interdigitated lipid phases induced by glycerol and polymyxin

Glycerol and polymyxin have been shown by X-ray diffraction to induce interdigitated bilayers in phosphatidylcholine (PC) and phosphatidylglycerol (PG), respectively (McDaniel, R.V., et al. (1983) Biochim. Biophys. Acta 731, 97-108; Ranck, J.-L. and Tocanne, J.-F. (1982) FEBS Lett. 143, 175-178). In the present study we have investigated the phase behavior of PC and PG in the presence of glycerol and polymyxin by differential scanning calorimetry and the use of fatty acid spin labels. Interdigitation causes a large increase in the order parameter of a fatty acid spin labeled near the terminal methyl, 16-doxylstearate, so that it was similar to that of a fatty acid labeled much closer to the polar head group region, 5-doxylstearate. Thus interdigitation abolishes the fluidity gradient found in a non-interdigitated bilayer. 16-Doxylstearate may be useful in detecting interdigitation of lipid bilayers caused by other substances. The different samples all went through two transitions on heating or cooling, or both. However, use of the fatty acid spin label showed that the molecular events during these transitions varies for different samples. The results suggested that PC-glycerol freezes from the liquid-crystalline phase into a non-interdigitated gel phase. This subsequently becomes interdigitated upon lowering the temperature a few degrees, in a low enthalpy transition. PG-polymyxin shows a similar behavior except that the enthalpy of the non-interdigitated gel to interdigitated phase transition is greater and the transition is reversible on heating. Thus on heating PG-polymyxin first goes through a transition from the interdigitated phase to a non-interdigitated gel phase and then, in a separate transition, to the liquid-crystalline phase. This occurs because the fatty acid chains in the presence of polymyxin become too disordered with increase in temperature to maintain the interdigitated state. PG-glycerol goes into the interdigitated state less readily than the other mixtures. If cooled rapidly, PG-glycerol freezes into a metastable phase which is more disordered than the interdigitated phase. It goes into the interdigitated phase in an exothermic transition on heating. An increase in fatty acid chain length causes greater steric hindrance to interdigitation but also increases the stabilizing energy gained by interdigitation.

Temporal processing dysfunction in schizophrenia

Schizophrenia may be associated with a fundamental disturbance in the temporal coordination of information processing in the brain, leading to classic symptoms of schizophrenia such as thought disorder and disorganized and contextually inappropriate behavior. Despite the growing interest and centrality of time-dependent conceptualizations of the pathophysiology of schizophrenia, there remains a paucity of research directly examining overt timing performance in the disorder. Accordingly, the present study investigated timing in schizophrenia using a well-established task of time perception. Twenty-three individuals with schizophrenia and 22 non-psychiatric control participants completed a temporal bisection task, which required participants to make temporal judgments about auditory and visually presented durations ranging from 300 to 600 ms. Both schizophrenia and control groups displayed greater visual compared to auditory timing variability, with no difference between groups in the visual modality. However, individuals with schizophrenia exhibited less temporal precision than controls in the perception of auditory durations. These findings correlated with parameter estimates obtained from a quantitative model of time estimation, and provide evidence of a fundamental deficit in temporal auditory precision in schizophrenia.

A randomized, double-blind, placebo-controlled trial of cidofovir gel for the treatment of acyclovir-unresponsive mucocutaneous herpes simplex virus infection in patients with AIDS

The safety and efficacy of cidofovir gel for treatment of acyclovir-unresponsive herpes simplex virus infections in AIDS patients was evaluated in a randomized, double-blind, multicenter trial. Cidofovir (0.3% or 1%) or placebo gel was applied once daily for 5 days. Ten of 20 cidofovir-treated and none of 10 placebo-treated patients had complete healing or >50% decreased area (P = .008); 30% of cidofovir-treated patients versus 0 placebo recipients had complete healing (P = .031). Viral shedding ceased in 13 (87%) of 15 cidofovir-treated and 0 of 9 placebo-treated patients (P = .00004). For cidofovir-treated patients, median time to complete or good response was 21 days, and median time to negative viral culture was 2 days (P = .025, P = .0001, respectively). Median lesion area decreases were 58% for cidofovir-treated versus 0 for placebo-treated patients (P = .005), and mean pain score changes were -1.84 versus -0.34 (P = .042). Application site reactions occurred in 25% of cidofovir-treated and 20% of placebo-treated patients; none was dose-limiting. Cidofovir therapy provided significant benefits in lesion healing, virologic effect, and pain reduction.

Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis: A Multicenter Retrospective Study of 377 Adult Patients from the United States

Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) is a rare, severe mucocutaneous reaction with few large cohorts reported. This multicenter retrospective study included patients with SJS/TEN seen by inpatient consultative dermatologists at 18 academic medical centers in the United States. A total of 377 adult patients with SJS/TEN between January 1, 2000 and June 1, 2015 were entered, including 260 of 377 (69%) from 2010 onward. The most frequent cause of SJS/TEN was medication reaction in 338 of 377 (89.7%), most often to trimethoprim/sulfamethoxazole (89/338; 26.3%). Most patients were managed in an intensive care (100/368; 27.2%) or burn unit (151/368; 41.0%). Most received pharmacologic therapy (266/376; 70.7%) versus supportive care alone (110/376; 29.3%)-typically corticosteroids (113/266; 42.5%), intravenous immunoglobulin (94/266; 35.3%), or both therapies (54/266; 20.3%). Based on day 1 SCORTEN predicted mortality, approximately 78 in-hospital deaths were expected (77.7/368; 21%), but the observed mortality of 54 patients (54/368; 14.7%) was significantly lower (standardized mortality ratio = 0.70; 95% confidence interval = 0.58-0.79). Stratified by therapy received, the standardized mortality ratio was lowest among those receiving both steroids and intravenous immunoglobulin (standardized mortality ratio = 0.52; 95% confidence interval 0.21-0.79). This large cohort provides contemporary information regarding US patients with SJS/TEN. Mortality, although substantial, was significantly lower than predicted. Although the precise role of pharmacotherapy remains unclear, co-administration of corticosteroids and intravenous immunoglobulin, among other therapies, may warrant further study.

Effect of basic protein from human central nervous system myelin on lipid bilayer structure

The effect of myelin basic protein from normal human central nervous system on lipid organization has been investigated by studying model membranes containing the protein by differential scanning calorimetry or electron spin resonance spectroscopy. Basic protein was found to decrease the phase transition temperature of dipalmitoyl phosphatidylglycerol, phosphatidic acid, and phosphatidylserine. The protein had a greater effect on the freezing temperature, measured from the cooling scan, than on the melting temperature, measured from the heating scan. These results are consistent with partial penetration of parts of the protein into the hydrocarbon region of the bilayer in the liquid crystalline state and partial freezing out when the lipid has been cooled below its phase transition temperature. The effect of the protein on fatty acid chain packing was investigated by using a series of fatty acid spin labels with the nitroxide group located at different positions along the chain. If the protein has not yet penetrated, it increases the order throughout the bilayer in the gel phase, probably by decreasing the repulsion between the lipid polar head groups. Above the phase transition temperature, when parts of it are able to pentrate, it decreases the motion of the lipid fatty acid chains greatly near the polar head group region, but has little or no effect near the interior of the bilayer. Upon cooling again the protein still decreases the motion near the polar head group region but increases it greatly in the interior. Thus, the protein penetrates partway into the bilayer, distorts the packing of the lipid fatty acid chains, and prevents recrystallization, thus decreasing the phase transition temperature. The magnitude of the effect varied with the lipid and was greatest for phosphatidic acid and phosphatidylglycerol. It could be reversed upon cooling for phosphatidylglycerol but not phosphatidic acid. The protein was only observed to decrease the phase transition temperature of phosphatidylserine upon cooling. It had only a small effect on phosphatidylethanolamine and no effect on phosphatidylcholine. Thus, the protein may penetrate to a different extent into different lipids even if it binds to the polar head group region by electrostatic interactions.

A carbohydrate-carbohydrate interaction between galactosylceramide-containing liposomes and cerebroside sulfate-containing liposomes: dependence on the glycolipid ceramide composition

Galactosylceramide (GalCer) and cerebroside sulfate (CBS) are the major glycolipids found in myelin. They occur in greater concentrations in this membrane than any other. Recently, it was reported that these two glycolipids can participate in a heterotypic carbohydrate-carbohydrate interaction [Hakomori et al. (1991) Glycoconjugate J. 8, 178]. In the present study, the effect of changes in the ceramide composition of both GalCer and CBS on this interaction has been examined. The interaction was monitored by measuring the aggregation of small unilamellar phosphatidylcholine/cholesterol liposomes containing GalCer with similar liposomes containing CBS, through the increase in optical density at 450 nm. Aggregation depends on the addition of a divalent cation and varies inversely with the ionic radius of the cation. Aggregation occurred at millimolar concentrations of divalent cation and was inhibited and reversed by the addition of EDTA. A lesser degree of homotypic self-aggregation of GalCer and of CBS liposomes also occurred in the presence of divalent cations, but the sum of this self-aggregation was significantly less than the heterotypic interaction between the two types of liposomes. Changes in the ceramide composition of GalCer and CBS significantly affected the extent of their interaction with each other. Increasing the fatty acid chain length of either GalCer or CBS resulted in increased aggregation. Hydroxylation of the fatty acid also increased the degree of aggregation of GalCer and CBS liposomes. These findings indicate that a divalent cation-mediated GalCer-CBS interaction could play a role in cell recognition and membrane adhesion phenomena such as the formation of compact multilamellar myelin.(ABSTRACT TRUNCATED AT 250 WORDS)

Patient-identified factors related to heart failure readmissions

BACKGROUND

Although readmission after hospitalization for heart failure has received increasing attention, little is known about its root causes. Prior investigations have relied on administrative databases, chart review, and single-question surveys.

METHODS AND RESULTS

We performed semistructured 30- to 60-minute interviews of patients (n=28) readmitted within 6 months of index heart failure admission. Established qualitative approaches were used to analyze and to interpret data. Interview findings were the primary focus of the study, but patient information and provider comments from chart data were also consulted. Patient median age was 61 years; 29% were nonwhite; 50% were married; 32% had preserved ejection fraction; and median time from discharge to readmission was 31 days. Reasons for readmission were multifactorial and not easily categorized into mutually exclusive reasons. Five themes emerged as reasons cited for hospital readmission: distressing symptoms, unavoidable progression of illness, influence of psychosocial factors, good but imperfect self-care adherence, and health system failures.

CONCLUSIONS

Our study provides the first systematic qualitative assessment of patient perspectives concerning heart failure readmission. Contrary to prior literature and distinct from what we found documented in the medical record, patient experiences were highly heterogeneous, not easily categorized as preventable or not preventable, and not easily attributed to a single cause. These findings suggest that future interventions designed to reduce heart failure readmissions should be multifaceted, should be systemic in nature, and should integrate patient input.

A pragmatic randomized clinical trial of behavioral activation for depressed pregnant women

OBJECTIVE

Depression among pregnant women is a prevalent public health problem associated with poor maternal and offspring development. Behavioral activation (BA) is a scalable intervention aligned with pregnant women's preference for nonpharmacological depression care. This is the first test of the effectiveness of BA for depression among pregnant women, which aimed to evaluate the effectiveness of BA as compared with treatment as usual (TAU).

METHOD

Pregnant women (mean age = 28.75 years; SD = 5.67) with depression symptoms were randomly assigned to BA (n = 86) or TAU (n = 77). Exclusion criteria included known bipolar or psychotic disorder or immediate self-harm risk. Follow-up assessment occurred 5 and 10 weeks postrandomization and 3 months postpartum using self-report measures of primary and secondary outcomes and putative targets.

RESULTS

Compared with TAU, BA was associated with significantly lower depressive symptoms (d = 0.34, p = .04) and higher remission (56.3% vs. 30.3%, p = .003). BA also demonstrated significant advantage on anxiety and perceived stress. Participants attended most BA sessions and reported high satisfaction. Participants in BA reported significantly higher levels of activation (d = 0.69, p < .0002) and environmental reward (d = 0.54, p < .003) than those who received TAU, and early change in both of these putative targets significantly mediated subsequent depression outcomes.

CONCLUSIONS

BA is effective for pregnant women, offering significant depression, anxiety, and stress benefits, with mediation analyses supporting the importance of putative targets of activation and environmental reward. (PsycINFO Database Record

Outcomes of Online Mindfulness-Based Cognitive Therapy for Patients With Residual Depressive Symptoms: A Randomized Clinical Trial

Importance

Patients with residual depressive symptoms face a gap in care because few resources, to date, are available to manage the lingering effects of their illness.

Objective

To evaluate the effectiveness for treating residual depressive symptoms with Mindful Mood Balance (MMB), a web-based application that delivers mindfulness-based cognitive therapy, plus usual depression care compared with usual depression care only.

Design, Setting, and Participants

This randomized clinical trial was conducted in primary care and behavioral health clinics at Kaiser Permanente Colorado, Denver. Adults identified with residual depressive symptoms were recruited between March 2, 2015, and November 30, 2018. Outcomes were assessed for a 15-month period, comprising a 3-month intervention interval and a 12-month follow-up period.

Interventions

Patients were randomized to receive usual depression care (UDC; n = 230) or MMB plus UDC (n = 230), which included 8 sessions delivered online for a 3-month interval plus minimal phone or email coaching support.

Main Outcomes and Measures

Primary outcomes were reduction in residual depressive symptom severity, assessed using the Patient Health Questionaire-9 (PHQ-9); rates of depressive relapse (PHQ-9 scores ≥15); and rates of remission (PHQ-9 scores <5). Secondary outcomes included depression-free days, anxiety symptoms (General Anxiety Disorder-7 Item Scale), and functional status (12-Item Short Form Survey).

Results

Among 460 randomized participants (mean [SD] age, 48.30 [14.89] years; 346 women [75.6%]), data were analyzed for the intent-to-treat sample, which included 362 participants (78.7%) at 3 months and 330 (71.7%) at 15 months. Participants who received MMB plus UDC had significantly greater reductions in residual depressive symptoms than did those receiving UDC only (mean [SE] PHQ-9 score, 0.95 [0.39], P < .02). A significantly greater proportion of patients achieved remission in the MMB plus UDC group compared with the UDC only group (PHQ-9 score, <5: β [SE], 0.38 [0.14], P = .008), and rates of depressive relapse were significantly lower in the MMB plus UDC group compared with the UDC only group (hazard ratio, 0.61; 95% CI, 0.39-0.95; P < .03). Compared with the UDC only group, the MMB plus UDC group had decreased depression-free days (mean [SD], 281.14 [164.99] days vs 247.54 [158.32] days; difference, -33.60 [154.14] days; t = -2.33; P = .02), decreased anxiety (mean [SE] General Anxiety Disorder-7 Item Scale score, 1.21 [0.42], P = .004), and improved mental functioning (mean [SE] 12-Item Short Form Survey score, -5.10 [1.37], P < .001), but there was no statistically significant difference in physical functioning.

Conclusions and Relevance

Use of MMB plus UDC resulted in significant improvement in depression and functional outcomes compared with UDC only. The MMB web-based treatment may offer a scalable approach for the management of residual depressive symptoms.

Trial Registration

ClinicalTrials.gov identifier: NCT02190968.

Factors affecting surface expression of glycolipids: influence of lipid environment and ceramide composition on antibody recognition of cerebroside sulfate in liposomes

The reactivity of the acidic glycolipid cerebroside sulfate (CBS) with antibody was studied as a function of its lipid environment in vesicles and of its ceramide composition. The lipid environment was varied by using phosphatidylcholine of varying chain length with cholesterol in a phosphatidylcholine:cholesterol:cerebroside sulfate molar ratio to glycolipid of 1:0.75:0.1. The ceramide structure of CBS was varied by using synthetic forms containing palmitic acid, lignoceric acid, or the corresponding alpha-hydroxy fatty acids. Reactivity with antibody was determined by measuring complement-mediated lysis of the vesicles containing a spin-label marker, tempocholine chloride. The data were analyzed by a theoretical model which gives relative values for the dissociation constant and concentration of antibodies within the antiserum which are able to bind to the glycolipid. If the phosphatidylcholine chain length was increased, increasing the bilayer thickness, only a small population of high-affinity antibodies were able to bind to cerebroside sulfate, suggesting decreased surface exposure of the glycosyl head group. A larger population of lower affinity antibodies were able to bind to it in a shorter chain length phosphatidylcholine environment. However, if the chain length of the cerebroside sulfate was increased, it could be recognized by more antibodies of lower affinity than the short chain length form, suggesting that an increase in chain length of the glycolipid increased surface exposure. Hydroxylation of the fatty acid inhibited antibody binding; only a smaller population of higher affinity antibodies was able to bind to the hydroxy fatty acid forms.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of posttranslational modifications to myelin basic protein on its ability to aggregate acidic lipid vesicles

When isolated from central nervous system myelin, myelin basic protein (MBP) exhibits charge microheterogeneity due to posttranslational deamidation, phosphorylation, and deimination of arginine to citrulline. These modifications are known to decrease the ability of MBP to aggregate acidic lipid vesicles and thus could regulate the ability of MBP to mediate adhesion between the intracellular surfaces of myelin. The effects of salt (KCl) concentration and the protein to lipid ratio on the ability of charge isomers of MBP to aggregate large unilamellar vesicles (LUVs) were investigated. Increased salt concentration from 10 to 100 mM caused increasing aggregation of LUVs by low concentrations of all charge isomers but did not eliminate the differences in their abilities to aggregate. All isomers were bound equally up to about 100 mM K+ but were dissociated at higher K+ concentrations. The degree of dissociation increased with increasing net negative charge of the isomer. At high concentrations all charge isomers except the form in which six arginine residues are converted to citrulline (C8) aggregated LUVs of phosphatidylcholine/phosphatidylserine (PC/PS) 8:2 (mol/mol) similarly and salt increased the aggregation to the same degree for all. There was less difference in the ability of the charge isomers, including C8, to aggregate LUVs with a lipid composition resembling that of the cytoplasmic leaflet of myelin (Cyt-LUVs) than for PC/PS LUVs. Furthermore, high salt concentrations (400 mM) did not dissociate any of the charge isomers from the Cyt-LUVs. These results suggest that the reason for inhibition of aggregating ability by charge modification is not increased charge repulsion of the protein but rather its reduced multivalency of net positive charge. They indicate further that the lipid composition of the cytoplasmic leaflet is ideally suited to permit MBP-mediated adhesion and that charge modifications of MBP would probably not affect adhesion of the intracellular surfaces of compact myelin where MBP concentration is high. However, charge modifications might affect adhesion in cytoplasm-containing regions of myelin such as the paranodal loops, where MBP concentration is low and where K+ concentration may vary in the range of 60-75 mM.

Trans interactions between galactosylceramide and cerebroside sulfate across apposed bilayers

The two glycosphingolipids galactosylceramide (GalC) and its sulfated form, cerebroside sulfate (CBS), are present at high concentrations in the multilayered myelin sheath and are involved in carbohydrate-carbohydrate interactions between the lipid headgroups. In order to study the structure of the complex of these two glycolipids by Fourier transform infrared (FTIR) spectroscopy, GalC dispersions were combined with CBS dispersions in the presence and absence of Ca(2+). The FTIR spectra indicated that a strong interaction occurred between these glycolipids even in the absence of Ca(2+). The interaction resulted in dehydration of the sulfate, changes in the intermolecular hydrogen bonding interactions of the sugar and other oxygens, decreased intermolecular hydrogen bonding of the amide C==O of GalC and dehydration of the amide region of one or both of the lipids in the mixture, and disordering of the hydrocarbon chains of both lipids. The spectra also show that Ca(2+) interacts with the sulfate of CBS. Although they do not reveal which other groups of CBS and GalC interact with Ca(2+) or which groups participate in the interaction between the two lipids, they do show that the sulfate is not directly involved in interaction with GalC, since it can still bind to Ca(2+) in the mixture. The interaction between these two lipids could be either a lateral cis interaction in the same bilayer or a trans interaction between apposed bilayers. The type of interaction between the lipids, cis or trans, was investigated using fluorescent and spin-label probes and anti-glycolipid antibodies. The results confirmed a strong interaction between the GalC and the CBS microstructures. They suggested further that this interaction caused the CBS microstructures to be disrupted so that CBS formed a single bilayer around the GalC multilayered microstructures, thus sequestering GalC from the external aqueous phase. Thus the CBS and GalC interacted via a trans interaction across apposed bilayers, which resulted in dehydration of the headgroup and interface region of both lipid bilayers. The strong interaction between these lipids may be involved in stabilization of the myelin sheath.

Investigation of the calcium-mediated association between the carbohydrate head groups of galactosylceramide and galactosylceramide I3 sulfate by electrospray ionization mass spectrometry

Calcium has been shown previously to cause aggregation of phosphatidylcholine/cholesterol liposomes containing galactosylceramide (GalCer) with similar liposomes containing cerebroside sulfate (galactosylceramide I3 sulfate) (CBS), suggesting that it mediates a carbohydrate-carbohydrate association between these two glycolipids. In order to determine if such an association occurs, the noncovalent complexes formed on addition of calcium chloride to GalCer and CBS in methanol were examined by positive and negative ion spray mass spectrometry. Monomeric Ca2+ complexes of both lipids were observed. In addition, Ca2+ also caused oligomerization of GalCer. Oligomerization of CBS anion was not seen, but dimers would not have been observed, as they would be neutral. However, Ca2+ caused heterotypic complexation of GalCer and CBS. Although these heterotypic complexes were of low abundance in methanol compared with the other monomeric and homotypic oligomeric positive ions formed at low declustering potentials, the heterotypic dimer [GalCer.CBS.Ca2+-H]+ had the greatest stability of all oligomers formed and was the only one to survive at high declustering potentials. Na+ did not cause oligomerization of GalCer in methanol indicating that the complexes of GalCer with Ca2+ are not caused by van der Waals interactions between the lipid moieties. GalCer and CBS are present in high concentrations in myelin. This Ca2+-mediated carbohydrate-carbohydrate interaction, which can bridge apposing bilayers, may be involved in adhesion of the extracellular surfaces of the myelin sheath.

Interaction of polymyxin B nonapeptide with anionic phospholipids

The interaction of polymyxin B nonapeptide (PMBN) and polymyxin B (PMB) with the anionic phospholipids phosphatidylserine (PS), dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidic acid (DPPA), and 1:1 mixtures (w/w) of DPPA and distearoylphosphatidylcholine (DSPC) was studied by calorimetry, electron spin resonance, and fluorescence spectrometry, electron microscopy, and fusion and leakage assays. The phase transition temperatures of DPPA and DPPG were very similar when bound to PMB or PMBN, indicating that the lipids are in a similar state when bound to the cationic peptides. Both PMB and PMBN caused the interdigitation of DPPG bilayers, suggesting that the penetration of hydrophobic side chains from a peptide bound electrostatically on the surface is sufficient to induce this phenomenon. Stopped-flow experiments revealed that PMBN and PMB induced the fusion of small unilamellar PS and large unilamellar DPPA-DSPC vesicles. The aggregation of vesicles was found to be diffusion-controlled process; the subsequent fusion took place with a frequency of 10(2)-(5 X 10(2] s-1 for small vesicles and 1-100 s-1 for large vesicles. The freeze-fracture replicas of the PMB-treated vesicles displayed 12-50-nm depressions on several superimposed bilayers, indicating the formation of stable lipid-PMB domains. Since the incubation with PMBN produced similar depressions only if the specimens were fixed, PMBN-induced domain formation seems to be a reversible rapid process. The differences in the phospholipid-peptide interactions are correlated with the differences in the physiological action of the antibiotic PMB and the nonbactericidal PMBN on the cell envelope of Gram-negative bacteria.