Formation of Assemblies on Cell Membranes by Secreted Proteins: Molecular Studies of Free Lambda Light Chain Aggregates Found on the Surface of Myeloma Cells
In this study, we describe the presence of λFLCs on the surface of myeloma cells. We found that cell surface-associated λFLC are bound directly to the membrane and in an aggregated form. Subsequently, membrane interaction studies revealed that λFLCs interact with saturated zwitterionic lipids such as phosphatidylcholine and phosphatidylethanolamine, and using automated docking, we characterize a potential recognition site for these lipids. Atomic force microscopy confirmed that membrane-associated
λFLCs are aggregated. Given our findings, we propose a model whereby individual FLCs show modest a...
Source: BJ Cell - July 4, 2013 Category: Biochemistry Authors: A T Hutchinson, A Malik, M B Berkahn, M Agostino, J To, J L Tacchi, S P Djordjevic, L Turnbull, C B Whitchurch, A B Edmundson, D R Jones, R L Raison, P A Ramsland Tags: BJ Cell Source Type: research
Sorting Nexin 27 (SNX27) associates with Zona Occludens-2 (ZO-2) and modulates the epithelial tight junction
Proteins of the sorting nexin (SNX) superfamily are characterized by the presence of a phox-homology (PX) domain and associate with phosphatidylinositol-3-monophosphate (PtdIns3P) rich regions of the endosomal system. SNX27 is the only sorting nexin that contains a PDZ domain. Here, we used a proteomic approach to identify a novel interaction between SNX27 and zona occludens-2 (ZO-2, TJP2), a component of the epithelial tight junction. The SNX27-ZO-2 interaction requires the PDZ domain of SNX27 and the C-terminal PDZ-binding motif of ZO-2. When tight junctions were perturbed by chelation of intracellular Ca2+, ZO-2 ...
Source: BJ Cell - July 4, 2013 Category: Biochemistry Authors: S Paul Zimmerman, C Lynn Hueschen, D Malide, S Lynn Milgram, M Peter Playford Tags: BJ Cell Source Type: research
Role of hypoxia and P1 receptor activation on the high affinity concentrative adenosine transporter CNT2 in PC12 cells
Under several adverse conditions, such as hypoxia or ischemia, extracellular levels of adenosine (Ado) upraise due to increased energy demands and ATP metabolism. Because extracellular Ado affects metabolism through G protein-coupled receptors, its regulation is of high adaptive importance. Concentrative nucleoside transporter 2 (CNT2) may play physiological roles beyond nucleoside salvage in brain as it does in other tissues. Even though nucleoside transport in brain has mostly been seen as of equilibrative-type, in this work we prove that the rat pheocromocytoma cell line PC12 shows a concentrative Ado transport of CNT2 ...
Source: BJ Cell - July 3, 2013 Category: Biochemistry Authors: L Medina-Pulido, M Molina-Arcas, C Justicia, E Soriano, F Burgaya, A Planas, M Pastor-Anglada Tags: BJ Metabolism Source Type: research
Mercury increases water permeability of a plant aquaporin through a non-cysteine related mechanism
Water transport across cellular membranes is mediated by a family of membrane proteins known as aquaporins (AQP). AQPs were first discovered based on their ability to be inhibited by mercurial compounds, an experiment which has followed the aquaporin field ever since. While mercury inhibition is most common, many AQPs are mercury insensitive. In plants, regulation of AQPs is important in order to cope with environmental changes. Plant plasma membrane aquaporins are known to be gated by phosphorylation, pH and Ca2+. We have previously solved the structure of the spinach AQP SoPIP2;1 in closed and open conformations a...
Source: BJ Cell - July 3, 2013 Category: Biochemistry Authors: A Frick, M Järvå, M Ekvall, P Uzdavinys, M Nyblom, S Törnroth-Horsefield Tags: BJ Plant Source Type: research
Mitochondrion-associated protein LRPPRC suppresses the initiation of basal levels of autophagy via enhancing Bcl-2 stability
The mitochondrion-associated protein LRPPRC interacts with one of microtubule-associated protein family MAP1S (originally named as C19ORF5) to form a complex. MAP1S interacts with LC3, the mammalian homologue of yeast autophagy marker ATG8 and one of the most important autophagy markers in mammalian cells, and helps the attachment of autophagosomes with microtubules for trafficking and recruitment of substrate mitochondria into autophagosomes for degradation. MAP1S activates autophagosomal biogenesis and degradation to remove mis-folded/aggregated proteins and dysfunctional organelles such as mitochondria and suppress oxid...
Source: BJ Cell - July 3, 2013 Category: Biochemistry Authors: J Zou, F Yue, X Jiang, W Li, J Yi, L Liu Tags: BJ Cell Source Type: research
A novel interplay between the ubiquitin-proteasome system and serine proteases during Drosophila development
The concentrations of the Drosophila proteasomal and extraproteasomal polyubiquitin receptors fluctuate in a developmentally regulated fashion. This fluctuation is generated by a previously unidentified proteolytic activity. Here we describe the purification, identification and characterization of this protease (endoproteinase I). Its expression increases sharply at L1-L2 larval stages, remains high until the second half of L3 stage then declines dramatically. This sharp decrease coincides precisely with the increase of polyubiquitin receptor concentrations in late L3 larvae, which suggests a tight developmental co-regulat...
Source: BJ Cell - June 28, 2013 Category: Biochemistry Authors: Z Lipinszki, E Klement, E Hunyadi-Gulyas, K F Medzihradszky, R Márkus, M Pál, P Deák, A Udvardy Tags: BJ Biomolecules Source Type: research
The Mitochondrial Carrier Rim2 Co-Imports Pyrimidine Nucleotides and Iron
Mitochondrial iron uptake is of key importance for both organelle function and cellular iron homeostasis. The mitochondrial carrier family members Mrs3 and Mrs4 (homologs of vertebrate mitoferrin) function in organellar iron supply, yet other low efficiency transporters may exist. In S. cerevisiae, overexpression of RIM2 (MRS12) encoding a mitochondrial pyrimidine nucleotide transporter can overcome the iron-related phenotypes of strains lacking both MRS3 and MRS4. Here, we show by in vitro transport studies that Rim2 mediates the transport of iron and other divalent metal ions across the mitochondrial inner membrane in a ...
Source: BJ Cell - June 26, 2013 Category: Biochemistry Authors: E M Froschauer, N Rietzschel, M R Hassler, M Binder, R J Schweyen, R Lill, U Mühlenhoff, G Wiesenberger Tags: BJ Metabolism Source Type: research
An aromatic amino acid in the CC1 domain plays a crucial role in the auto-inhibitory mechanism of STIM1
In this study, we first predicted a short inhibitory domain (310-317) in human STIM1 that might determine the different localizations of human and C. elegans STIM1 in resting cells. Next, we confirmed the prediction and further identified an aromatic amino acid residue Y316 that played a crucial role in maintaining STIM1 in a closed conformation in quiescent cells. Full length STIM1-Y316A formed constitutive clusters near the plasma membrane and activated the CRAC channel in the resting state when co-expressed with Orai1. And the introduction of Y316A mutation caused the higher-order oligolization of in vitro purified STIM...
Source: BJ Cell - June 25, 2013 Category: Biochemistry Authors: J Yu, H Zhang, M ZHANG, Y Deng, H Wang, J Lu, T Xu, P Xu Tags: BJ Signal Source Type: research
Channel-mediated lactic acid transport: a novel function for aquaglyceroporins in bacteria
In conclusion, we have functionally analyzed the largest set of bacterial MIPs and demonstrated that the lactic acid membrane permeability of bacteria can be regulated by aquaglyceroporins. (Source: BJ Cell)
Source: BJ Cell - June 25, 2013 Category: Biochemistry Authors: G Patrick Bienert, B Desguin, F Chaumont, P Hols Tags: BJ Cell Source Type: research
Zinc coordination by the DHHC cysteine-rich domain of the palmitoyltransferase Swf1
S-acylation, commonly known as palmitoylation, is a widespread post-translational modification of proteins that consists in the tioestherification of one or more cysteine residues with long chain fatty acids. This modification is catalyzed by a family of palmitoyltransferases (PATs), characterized by the presence of a 50-residue long Cysteine-Rich Domain (DHHC-CRD). To gain knowledge on the structure-function relationships of these proteins, we carried out a random-mutagenesis assay designed to uncover essential amino acids in Swf1, the yeast PAT responsible for the palmitoylation of SNARE proteins. We identified 21 novel ...
Source: BJ Cell - June 24, 2013 Category: Biochemistry Authors: A González Montoro, R Quiroga, J Valdez Taubas Tags: BJ Biomolecules Source Type: research
The transport of carboxylic acids and important role of Jen1p transporter during the development of yeast colonies
In this study, we show that colony cells can use two transport mechanisms to import lactic acid: a "saturable" component of the transport, which requires the presence of functional Jen1p transporter and a "non-saturable" component (diffusion) that is independent of Jen1p. During colony development, the efficiency of both transport components changes similarly in central and outer colonial cells. While the lactate uptake capacity of central cells gradually decreases during colony development, the lactate uptake capacity of outer cells peaks during the alkali phase and is also kept relatively high in the 2nd acidic phase. Th...
Source: BJ Cell - June 21, 2013 Category: Biochemistry Authors: S Paiva, D Strachotová, H Kučerová, O Hlaváček, S Mota, M Casal, Z Palková, L Váchová Tags: BJ Cell Source Type: research
The use of alternative polyadenylation sites renders {beta}1- integrin mRNA isoforms with differential stability during mammary gland development
Integrins are heterodimeric cell surface adhesion receptors that play a critical role in tissue development. Characterization of the full length mRNA encoding the β1 subunit (Itgb1) revealed an alternative functional cleavage and polyadenylation site that yields a new Itgb1 mRNA isoform, 578bp shorter than that previously reported. Using a variety of experimental and bioinformatic approaches, we found that the two Itgb1 isoforms are expressed at different levels in a variety of mouse tissues, including the mammary gland, where they are differentially regulated at successive developmental stages. The longer mRNA spec...
Source: BJ Cell - June 21, 2013 Category: Biochemistry Authors: J Naipauer, A Gattelli, M Sol Degese, V Slomiansky, E Wertheimer, J LaMarre, L Castilla, M Abba, E Claudia Kordon, O Adrian Coso Tags: BJ Cell Source Type: research
A general anesthetic propofol inhibits aquaporin-4 in the presence of Zn2{+}
Aquaporin-4 (AQP4), a water channel protein that is predominantly expressed in astrocyte end-feet, plays an important role in the brain edema formation, thereby considered to be a potential therapeutic target. Using a stopped-flow analysis, we showed that propofol (2,6-diisopropylphenol), a general anesthetic drug, profoundly inhibited the osmotic water permeability of AQP4 proteoliposomes in the presence of Zn2+. This propofol inhibition was not observed in AQP1, suggesting the specificity for AQP4. In addition, the inhibitory effects of propofol could be reversed by the removal of Zn2+ ion. Other lipid memb...
Source: BJ Cell - June 17, 2013 Category: Biochemistry Authors: J Kato, M Kato Hayashi, S Aizu, Y Yukutake, J Takeda, M Yasui Tags: BJ Cell Source Type: research
Evolutionarily conserved structural changes in phosphatidylinositol 5-phosphate 4-kinase (PI5P4K) isoforms are responsible for differences in enzyme activity and localisation
We describe here a detailed molecular exploration of human PI5P4Ks α, β and γ, as well as their fly and worm homologs, to understand how and why these differences came to be. The intrinsic ATPase activities of the three isoforms are very similar, and we show that differences in their G-loop regions can account for much of their wide differences in lipid kinase activity. We have also undertaken an extensive in silico evolutionary study of the PI5P4K family, and show experimentally that the single PI5P4K homologs from C. elegans and D. melanogaster are as widely different in activity as the most divergen...
Source: BJ Cell - June 12, 2013 Category: Biochemistry Authors: J H Clarke, R F Irvine Tags: BJ Signal Source Type: research
Ras palmitoylation is necessary for N-Ras activation and signal propagation in growth factor signalling
Ras GTPases undergo post-translational modifications that govern their sub-cellular
trafficking and localization. In particular, palmitoylation at the Golgi tags N-Ras and H-Ras
for exocytotic transport and residency at the plasma membrane (PM). Following
depalmitoylation, PM-Ras redistributes to all subcellular membranes causing an accumulation
of palmitate-free Ras at endomembranes, including Golgi and endoplasmic reticulum.
Palmitoylation is unanimously regarded as a critical modification at the crossroads of Rasactivity
and trafficking control but its precise relevance to native, wild-type Ras function in
growth...
Source: BJ Cell - June 12, 2013 Category: Biochemistry Authors: S Song, A Hennig, K Schubert, R Markwart, P Schmidt, I A. Prior, F Böhmer, I Rubio Tags: BJ Signal Source Type: research
