Mechanism of complement cytolysis and the concept of channel-forming proteins

1984 ◽  
Vol 306 (1129) ◽  
pp. 311-324 ◽  
Keyword(s):  
Protein Complexes ◽  
Supramolecular Complexes ◽  
Reaction Sequence ◽  
Native Proteins ◽  
Streptolysin O ◽  
Transmembrane Pores ◽  
Target Cell Membrane ◽  
Membrane Bound ◽  
Self Association ◽  
Protein Channels

Complement damages membranes via the terminal reaction sequence that leads to the formation of membrane-bound, macromolecular C5b-9(m) protein complexes. These complexes represent C5b-8 monomers to which varying numbers of C9 molecules can be bound. Complexes carrying high numbers of C9 ( ca . 6/8-12/16?) exhibit the morphology of hollow protein channels. Because they are embedded within the lipid bilayer, aqueous transmembrane pores are generated that represent the primary lesions caused by complement in the target cell membrane. Many other proteins damage membranes by forming channels in a manner analogous to the C5b-9(m) complex. Two prototypes of bacterial exotoxins, Staphylococcus aureus α-toxin and streptolysin-O, are discussed in this context, and attention is drawn to the numerous analogies existing among these protein systems. Common to all is the process of self-association of the native proteins to form supramolecular complexes. This event is in turn accompanied by a unique transition of the molecules from a hydrophilic to an amphiphilic state.

scholarly journals Functional characterization of human Polycomb-like 3 isoforms identifies them as components of distinct EZH2 protein complexes

2011 ◽  
Vol 434 (2) ◽  
pp. 333-342 ◽  
Author(s):  
Gaylor Boulay ◽  
Claire Rosnoblet ◽  
Cateline Guérardel ◽  
Pierre-Olivier Angrand ◽  
Dominique Leprince
Keyword(s):  
Cell Fate ◽  
Target Genes ◽  
Protein Complexes ◽  
Functional Characterization ◽  
Polycomb Group ◽  
Phd Finger ◽  
Reverse Transcription Pcr ◽  
Tudor Domain ◽  
Self Association ◽  
Polycomb Repressive Complex 1

PcG (Polycomb group) proteins are conserved transcriptional repressors essential to regulate cell fate and to maintain epigenetic cellular memory. They work in concert through two main families of chromatin-modifying complexes, PRC1 (Polycomb repressive complex 1) and PRC2–4. In Drosophila, PRC2 contains the H3K27 histone methyltransferase E(Z) whose trimethylation activity towards PcG target genes is stimulated by PCL (Polycomb-like). In the present study, we have examined hPCL3, one of its three human paralogues. Through alternative splicing, hPCL3 encodes a long isoform, hPCL3L, containing an N-terminal TUDOR domain and two PHDs (plant homeodomains) and a smaller isoform, hPCL3S, lacking the second PHD finger (PHD2). By quantitative reverse transcription–PCR analyses, we showed that both isoforms are widely co-expressed at high levels in medulloblastoma. By co-immunoprecipitation analyses, we demonstrated that both isoforms interact with EZH2 through their common TUDOR domain. However, the hPCL3L-specific PHD2 domain, which is better conserved than PHD1 in the PCL family, is also involved in this interaction and implicated in the self-association of hPCL3L. Finally, we have demonstrated that both hPCL3 isoforms are physically associated with EZH2, but in different complexes. Our results provide the first evidence that the two hPCL3 isoforms belong to different complexes and raise important questions about their relative functions, particularly in tumorigenesis.

scholarly journals Comparison of lipid aggregation and self-aggregation activities of pulmonary surfactant-associated protein A

1996 ◽  
Vol 313 (2) ◽  
pp. 683-689 ◽  
Author(s):  
Miguel L. F. RUANO ◽  
Eugenio MIGUEL ◽  
Jesus PEREZ-GIL ◽  
Cristina CASALS
Keyword(s):  
Protein A ◽  
Maximal Activity ◽  
Surfactant Protein ◽  
Threshold Concentration ◽  
Carbohydrate Binding ◽  
Oligosaccharide Moiety ◽  
Membrane Bound ◽  
Self Association ◽  
Aggregation Activity ◽  
Self Aggregation

1. We compared the Ca2+ dependence of the self-aggregation of surfactant protein A (SP-A) with that of vesicle aggregation induced by SP-A. The Ca2+ concentration required for half-maximal activity of lipid aggregation was 0.74±0.29 μM (n = 4) for pig SP-A and 98±5 μM (n = 2) for dog SP-A. In contrast, the threshold concentration of Ca2+ required to induce self-association of both pig and dog SP-A was 0.5 mM. The Ca2+ concentration needed for half-maximal self-association was 2.36±0.15 mM (n = 4) and 0.70±0.06 mM (n = 2) for pig and dog SP-A respectively. 2. We also compared the effect of Ca2+ on the trypsin sensitivity of lipid-free and membrane-bound SP-A. At 1 μM Ca2+, the tryptic digestion patterns of dog and pig lipid-free SP-A were quite different. Dog SP-A was very sensitive to proteolysis, being almost completely digested by 30 min, while pig SP-A was very resistant, even after 12 h. After protein aggregation of lipid-free SP-A (at 5 mM Ca2+), the accessibility of the trypsin cleavage targets of the protein depended on the SP-A species (self-aggregated pig SP-A became more sensitive to degradation than its non-aggregated form, whereas self-aggregated dog SP-A was less susceptible). In contrast, membrane-bound SP-A, from either pig or dog, was clearly protected from trypsin degradation at both low (1 μM) or high (1 mM) Ca2+ concentrations. The protection was slightly higher at 1 mM Ca2+ when the extent of lipid/SP-A aggregates was maximal. 3. On the other hand, vesicle aggregation activity of SP-A was decreased by 30-40% by removing the oligosaccharide moiety of the protein, whereas self-aggregation was not influenced by deglycosylation. The presence of mannan (at concentrations not lower than 10 μg/μl) decreased vesicle aggregation induced by dog and pig SP-A by a mechanism that is independent of the binding of mannan to the carbohydrate-binding domain of SP-A. Self-aggregation of SP-A was not affected by the presence of sugars. 4. From these results, we conclude that: (1) the process of lipid aggregation induced by SP-A cannot be correlated with that of self-association of the protein occurring at supramillimolar concentrations of Ca2+; and (2) the N-linked carbohydrate moiety of SP-A and the ability of SP-A to bind carbohydrates are not involved in lipid aggregation.

scholarly journals Supramolecular Complexes Mediate Selenocysteine Incorporation In Vivo

2006 ◽  
Vol 26 (6) ◽  
pp. 2337-2346 ◽  
Author(s):  
Andrea Small-Howard ◽  
Nadya Morozova ◽  
Zoia Stoytcheva ◽  
Erin P. Forry ◽  
John B. Mansell ◽  
...  
Keyword(s):  
Protein Complexes ◽  
Elongation Factor ◽  
Supramolecular Complexes ◽  
Liver Protein ◽  
Mrna Levels ◽  
Nonsense Mediated Decay ◽  
Two Factors ◽  
Protein Nucleic Acid

ABSTRACT Selenocysteine incorporation in eukaryotes occurs cotranslationally at UGA codons via the interactions of RNA-protein complexes, one comprised of selenocysteyl (Sec)-tRNA[Ser]Sec and its specific elongation factor, EFsec, and another consisting of the SECIS element and SECIS binding protein, SBP2. Other factors implicated in this pathway include two selenophosphate synthetases, SPS1 and SPS2, ribosomal protein L30, and two factors identified as binding tRNA[Ser]Sec, termed soluble liver antigen/liver protein (SLA/LP) and SECp43. We report that SLA/LP and SPS1 interact in vitro and in vivo and that SECp43 cotransfection increases this interaction and redistributes all three proteins to a predominantly nuclear localization. We further show that SECp43 interacts with the selenocysteyl-tRNA[Ser]Sec-EFsec complex in vitro, and SECp43 coexpression promotes interaction between EFsec and SBP2 in vivo. Additionally, SECp43 increases selenocysteine incorporation and selenoprotein mRNA levels, the latter presumably due to circumvention of nonsense-mediated decay. Thus, SECp43 emerges as a key player in orchestrating the interactions and localization of the other factors involved in selenoprotein biosynthesis. Finally, our studies delineating the multiple, coordinated protein-nucleic acid interactions between SECp43 and the previously described selenoprotein cotranslational factors resulted in a model of selenocysteine biosynthesis and incorporation dependent upon both cytoplasmic and nuclear supramolecular complexes.

scholarly journals Supramolecularity creates nonstandard protein ligands.

1999 ◽  
Vol 46 (4) ◽  
pp. 841-851 ◽  
Author(s):  
B Piekarska ◽  
J Rybarska ◽  
B Stopa ◽  
G Zemanek ◽  
M Król ◽  
...  
Keyword(s):  
Liquid Crystalline ◽  
Structural Changes ◽  
Structural Instability ◽  
Antigen Binding ◽  
Experimental Science ◽  
Water Solutions ◽  
Protein Ligands ◽  
Native Proteins ◽  
Receptor Sites ◽  
Self Association

Congo red and a group of structurally related dyes long used to stain amyloid proteins are known to associate in water solutions. The self-association of some dyes belonging to this group appears particularly strong. In water solutions their molecules are arranged in ribbon-like micellar forms with liquid crystalline properties. These compounds have recently been found to form complexes with some native proteins in a non-standard way. Gaps formed by the local distribution of beta-sheets in proteins probably represent the receptor sites for these dye ligands. They may result from higher structural instability in unfolding conditions, but also may appear as long range cooperative fluctuations generated by ligand binding. Immunoglobulins G were chosen as model binding proteins to check the mechanism of binding of these dyes. The sites of structural changes generated by antigen binding in antibodies, believed to act as a signal propagated to distant parts of the molecule, were assumed to be suitable sites for the complexation of liquid-crystalline dyes. This assumption was confirmed by proving that antibodies engaged in immune complexation really do bind these dyes; as expected, this binding affects their function by significantly enhancing antigen binding and simultaneously inhibiting C1q attachment. Binding of these supramolecular dyes by some other native proteins including serpins and their natural complexes was also shown. The strict dependence of the ligation properties on strong self-assembling and the particular arrangement of dye molecules indicate that supramolecularity is the feature that creates non-standard protein ligands, with potential uses in medicine and experimental science.

scholarly journals A dual function of TMEM70 in OXPHOS: assembly of complexes I and V

2019 ◽  
Author(s):  
Laura Sánchez-Caballero ◽  
Dei M. Elurbe ◽  
Fabian Baertling ◽  
Sergio Guerrero-Castillo ◽  
Mariel van den Brand ◽  
...  
Keyword(s):  
Protein Complexes ◽  
Congenital Defects ◽  
Dual Function ◽  
Inner Mitochondrial Membrane ◽  
Independent Evidence ◽  
Membrane Recruitment ◽  
Oxphos System ◽  
Membrane Bound ◽  
Assembly Intermediate ◽  
The Stability

AbstractProtein complexes from the oxidative phosphorylation (OXPHOS) system are assembled with the help of proteins called assembly factors. We here delineate the function of the inner mitochondrial membrane protein TMEM70, in which mutations have been linked to OXPHOS deficiencies, using a combination of BioID, complexome profiling and coevolution analyses. TMEM70 interacts with complex I and V and for both complexes the loss of TMEM70 results in the accumulation of an assembly intermediate followed by a reduction of the next assembly intermediate in the pathway. This indicates that TMEM70 has a role in the stability of membrane-bound subassemblies or in the membrane recruitment of subunits into the forming complex. Independent evidence for a role of TMEM70 in OXPHOS assembly comes from evolutionary analyses. The TMEM70/TMEM186/TMEM223 protein family, of which we show that TMEM186 and TMEM223 are mitochondrial in human as well, only occurs in species with OXPHOS complexes. Our results validate the use of combining complexomics with BioID and evolutionary analyses in elucidating congenital defects in protein complex assembly.

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