Specific Adhesion of Membranes Simultaneously Supports Dual Heterogeneities in Lipids and Proteins

Membrane adhesion is a vital component of many biological processes. Heterogeneities in lipid and protein composition are often associated with the adhesion site. These heterogeneities are thought to play functional roles in facilitating signalling. Here we experimentally examine this phenomenon using model membranes made of a mixture of lipids that is near a phase boundary at room temperature. Non-adherent model membranes are in a well-mixed, disordered-fluid lipid phase indicated by homogeneous distribution of a fluorescent dye that is a marker for the fluid-disordered (Ld) phase. We specifically adhere membranes to a flat substrate bilayer using biotin–avidin binding. Adhesion produces two types of coexisting heterogeneities: an ordered lipid phase that excludes binding proteins and the fluorescent membrane dye, and a disordered lipid phase that is enriched in both binding proteins and membrane dye compared with the non-adhered portion of the same membrane. Thus, a single type of adhesion interaction (biotin–avidin binding), in an initially-homogeneous system, simultaneously stabilizes both ordered-phase and disordered-phase heterogeneities that are compositionally distinct from the non-adhered portion of the vesicle. These heterogeneities are long-lived and unchanged upon increased temperature.This work was funded by start-up funds from The University of Texas at Austin (UT Austin) to VDG. MR was supported in part by undergraduate research fellowships from UT Austin. We are grateful to Professor Jeanne Stachowiak (Biomedical Engineering, UT Austin) for helpful conversations about membrane formation and to her and her group for technical assistance. We thank Professor Ernst-Ludwig Florin (Physics, UT Austin) for the extruder and for cover glasses. We thank Professor Lauren Ehrlich (Molecular Biosciences, UT Austin) for helpful conversations about the immune synapse.Center for Nonlinear Dynamic

MICA-129 dimorphism and soluble MICA are associated with the progression of multiple myeloma

Natural killer (NK) cells are immune innate effectors playing a pivotal role in the immunosurveillance of multiple myeloma (MM) since they are able to directly recognize and kill MM cells. In this regard, among activating receptors expressed by NK cells, NKG2D represents an important receptor for the recognition of MM cells, being its ligands expressed by tumor cells, and being able to trigger NK cell cytotoxicity. The MHC class I-related molecule A (MICA) is one of the NKG2D ligands; it is encoded by highly polymorphic genes and exists as membrane-bound and soluble isoforms. Soluble MICA (sMICA) is overexpressed in the serum of MM patients, and its levels correlate with tumor progression. Interestingly, a methionine (Met) to valine (Val) substitution at position 129 of the α2 heavy chain domain classifies the MICA alleles into strong (MICA-129Met) and weak (MICA-129Val) binders to NKG2D receptor. We addressed whether the genetic polymorphisms in the MICA-129 alleles could affect MICA release during MM progression. The frequencies of Val/Val, Val/Met, and Met/Met MICA-129 genotypes in a cohort of 137 MM patients were 36, 43, and 22%, respectively. Interestingly, patients characterized by a Val/Val genotype exhibited the highest levels of sMICA in the sera. In addition, analysis of the frequencies of MICA-129 genotypes among different MM disease states revealed that Val/Val patients had a significant higher frequency of relapse. Interestingly, NKG2D was downmodulated in NK cells derived from MICA-129Met/Met MM patients. Results obtained by structural modeling analysis suggested that the Met to Val dimorphism could affect the capacity of MICA to form an optimal template for NKG2D recognition. In conclusion, our findings indicate that the MICA-129Val/Val variant is associated with significantly higher levels of sMICA and the progression of MM, strongly suggesting that the usage of soluble MICA as prognostic marker has to be definitely combined with the patient MICA genotype

Graphene adhesion on mica: Role of surface morphology

We investigate theoretically the adhesion and electronic properties of graphene on a muscovite mica surface using the density functional theory (DFT) with van der Waals (vdW) interactions taken into account (the vdW-DF approach). We found that irregularities in the local structure of cleaved mica surface provide different mechanisms for the mica-graphene binding. By assuming electroneutrality for both surfaces, the binding is mainly of vdW nature, barely exceeding thermal energy per carbon atom at room temperature. In contrast, if potassium atoms are non uniformly distributed on mica, the different regions of the surface give rise to $n$- or $p$-type doping of graphene. In turn, an additional interaction arises between the surfaces, significantly increasing the adhesion. For each case the electronic states of graphene remain unaltered by the adhesion. It is expected, however, that the Fermi level of graphene supported on realistic mica could be shifted relative to the Dirac point due to asymmetry in the charge doping. Obtained variations of the distance between graphene and mica for different regions of the surface are found to be consistent with recent atomic force microscopy experiments. A relative flatness of mica and the absence of interlayer covalent bonding in the mica-graphene system make this pair a promising candidate for practical use.Comment: 6 pages, 3 figure

How Educators Can Eradicate Disparities in School Discipline: A Briefing Paper on School-Based Interventions

The number of students issued suspensions in U.S. schools continues to be extremely high, resulting in thousands of students missing school every day. Simultaneously,disparities in school suspension continue to worsen, indicating that students in some groups are missing school far more often and disproportionately(particularly, boys, African American students, students with disabilities, and in some regions, Latino and American Indian students). These disparities are also true of referrals to law enforcement and school-based arrests nationwide. According to recent data collected by the Department of Education's Office for Civil Rights, students of color made up 75% of referrals to law enforcement and 79% of schoolbased arrests, even while students of color comprise 39% of the nation's public school population.Punitive school discipline matters tremendously to the educational opportunity of young people: New knowledge on school discipline shows that even a single suspension or a single referral to the juvenile court system increases the odds of low achievement and dropping out of school altogether. Moreover, research shows that schools and educators -- not just students themselves -- make a difference in how discipline is meted out

Impacto da sensibilização anti -MICA pré -transplante na rejeição e sobrevida do enxerto

Background: Evidence supporting deleterious effect of preformed major histocompatibility class I chain-related A (MICA) antibodies in rejection incidence and graft survival is still unclear. Methods: Retrospective analysis of 554 kidney transplanted patients. Comparison between positive or negative for MICA antibodies patients was performed to characterize sensitizing triggers. Further classification according to pre-transplant flow cytometry-recorded anti–MICA and/or anti-human leukocyte antigen (HLA) antibodies was made to determine first year rejection incidence and graft survival. Multivariate analysis was applied to determine predictors for acute rejection. Results: Pre-formed anti-MICA antibodies were detected in 41 patients (7.4%). HLA sensitization, blood transfusions and pregnancies were frequently found in anti-MICA+ patients but only pre-formed anti-HLA class I antibodies showed independent association (OR 2.67, p= 0.02). Comparing to MICA-/HLA–, MICA-/HLA+ group presented significantly lower first year rejection-free survival (78.6% vs. 89.3%, p< 0.01), mostly occurred in the first six months, while no difference was found in MICA+/HLA– (88.9% vs. 89.3%, p= ns). MICA-/HLA+ showed independent impact in rejection (OR 2.09, p= 0.03), while no evidence was found in MICA+/HLA- (OR 1.08, p= ns). At 4 years, MICA-/HLA+ group presented lower graft survival (85.8% vs. 95.3%, p= 0.03). Again, no difference was found in MICA+/HLA- group (95.1% vs. 95.3%, p= ns). Conclusion: Our results do not support HLA-independent deleterious pathogenic role of pre-formed MICA antibodies on first year rejection incidence and graft survival.Introdução: O efeito deletério dos anticorpos para antigénios MICA (major histocompatibility class I chain-related A) na incidência de rejeição aguda e sobrevida do enxerto ainda não está consensualmente estabelecido. Metódos: Estudo retrospetivo de 554 transplantados renais. A análise comparativa entre doentes positivos e negativos para anticorpos anti-MICA pré-formados foi realizada para avaliar eventos sensibilizadores. A incidência de rejeição aguda no primeiro ano pós transplante renal e a sobrevida do enxerto renal foram determinadas consoante o resultado da citometria de fluxo pré-transplante para anticorpos anti-MICA e/ou anti- HLA (anti-human leukocyte antigen). Aplicou-se um modelo de análise multivariada para identificação de preditores independentes para rejeição aguda. Resultados: Foram identificados 41 doentes (7.4%) com anticorpos anti-MICA pré formados. A sensibilização para HLA, as transfusões sanguíneas e gestações prévias foram mais frequentes nos doentes MICA + mas apenas a presença de anticorpos anti-HLA classe I apresentou uma associação independente (OR 2.67, p= 0.02). Comparativamente ao grupo MICA-/HLA–, o grupo MICA-/HLA+ apresentou menor sobrevida livre de rejeição ao 1º ano (78.6% vs. 89.3%, p< 0.01), maioritariamente ocorrida nos primeiros seis meses, enquanto que nenhuma diferença foi encontrada com o grupo MICA+/HLA– (88.9% vs. 89.3%, p= ns). Apenas o status MICA-/HLA+ teve impacto independente na incidência de rejeição (OR 2.09, p= 0.03), ao contrário do status MICA+/HLA- (OR 1.08, p= ns). O grupo MICA-/HLA+ apresentou menor sobrevida do enxerto censurada para a morte aos 4 anos (85.8% vs. 95.3%, p= 0.03), não se verificando diferenças no grupo MICA+/HLA- (95.1% vs. 95.3%, p= ns). Conclusão: Os nossos resultados não suportam um efeito deletério dos anticorpos pré-formados para MICA, independente da sensibilização HLA, na incidência de rejeição aguda no 1º ano pós transplante e na sobrevida do enxerto

Probing the structure of the cold dark matter halo with ancient mica

Mica can store (for >1 Gy) etchable tracks caused by atoms recoiling from WIMPs. Ancient mica is a directional detector despite the complex motions it makes with respect to the WIMP "wind". We can exploit the properties of directionality and long integration time to probe for structure in the dark matter halo of our galaxy. We compute a sample of possible signals in mica for a plausible model of halo structure.Comment: 7 pages, 2 figure

Matched sizes of activating and inhibitory receptor/ligand pairs are required for optimal signal integration by human Natural Killer cells

It has been suggested that receptor-ligand complexes segregate or co-localise within immune synapses according to their size, and this is important for receptor signaling. Here, we set out to test the importance of receptor-ligand complex dimensions for immune surveillance of target cells by human Natural Killer (NK) cells. NK cell activation is regulated by integrating signals from activating receptors, such as NKG2D, and inhibitory receptors, such as KIR2DL1. Elongating the NKG2D ligand MICA reduced its ability to trigger NK cell activation. Conversely, elongation of KIR2DL1 ligand HLA-C reduced its ability to inhibit NK cells. Whereas normal-sized HLA-C was most effective at inhibiting activation by normal-length MICA, only elongated HLA-C could inhibit activation by elongated MICA. Moreover, HLA-C and MICA that were matched in size co-localised, whereas HLA-C and MICA that were different in size were segregated. These results demonstrate that receptor-ligand dimensions are important in NK cell recognition, and suggest that optimal integration of activating and inhibitory receptor signals requires the receptor-ligand complexes to have similar dimensions

Structure and Phase Transitions of Alkyl Chains on Mica

We use molecular dynamics as a tool to understand the structure and phase transitions [Osman et. al. J. Phys. Chem. B 2000, 104, 4433; 2002, 106, 653] in alkylammonium micas. The consistent force field 91 is extended for accurate simulation of mica and related minerals. We investigate mica sheets with 12 octadecyltrimethylammonium (C18) ions or 12 dioctadecyldimethylammonium (2C18) ions, respectively, as single and layered structures at different temperatures with periodicity in the xy plane by NVT dynamics. The alkylammonium ions reside preferably above the cavities in the mica surface with an aluminum-rich boundary. The nitrogen atoms are 380 to 390 pm distant to the superficial silicon-aluminum plane. With increasing temperature, rearrangements of C18 ions on the mica surface are found, while 2C18 ions remain tethered due to geometric restraints. We present basal-plane spacings in the duplicate structures, tilt angles of the alkyl chains, and gauche-trans ratios to analyze the chain conformation. Also, the individual phase transitions of the two systems on heating are explained. Where experimental data are available, the agreement is very good. We propose a geometric parameter lamba for the saturation of the surface with alkyl chains, which determines the preferred self-assembly pattern, i.e., islands, intermediate, or continuous. Lambda also determines the tilt angles in continuous layers on mica or other surfaces. The thermal decomposition appears to be a Hofmann elimination with mica as a base-template.Comment: 45 pages with 6 tables and 5 figure