Targeting of the GRIP domain to the trans-Golgi network is conserved from protists to animals

The GRIP domain, found in a family of coiled-coil peripheral membrane Golgi proteins, is a specific targeting sequence for the trans-Golgi network of animal cells. In this study we show that a coiled-coil protein with a GRIP domain occurs in the primitive eukaryote, Trypanosoma brucei, and that reporter proteins containing this domain can be used as a marker for the poorly characterized trans Golgi/trans-Golgi network of trypanosomatid parasites. The T. brucei GRIP domain, when fused to the carboxyl terminus of the green fluorescent protein (GFP-TbGRIP), was efficiently localized to the Golgi apparatus of transfected COS cells. Overexpression of GFP-TbGRIP in COS cells displaced the endogenous GRIP protein, GCC1p, from the Golgi apparatus indicating that the trypanosomatid and mammalian GRIP sequences interact with similar membrane determinants. GFP fusion proteins containing either the T. brucei GRIP domain or the human p230 GRIP (p230GRIP) domain were also expressed in the trypanosomatid parasite, Leishmania mexicana, and localized by fluorescence and immuno-electron microscopy to the trans face of the single Golgi apparatus and a short tubule that extended from the Golgi apparatus. Binding of GFP-p230GRIP to Golgi membranes in L. mexicana was abrogated by mutation of a critical tyrosine residue in the p230 GRIP domain. The levels of GFP-GRIP fusion proteins were dramatically reduced in stationary-phase L. mexicana promastigotes, suggesting that specific Golgi trafficking steps may be down-regulated as the promastigotes cease dividing. This study provides a protein marker for the trans-Golgi network of trypanosomatid parasites and suggests that the GRIP domain binds to a membrane component that has been highly conserved in eukaryotic evolution.     

Phytoextraction of high value elements and contaminants from mining and mineral wastes: opportunities and limitations

Plant and Soil - Phytoextraction is an in situ technique that can be applied to minerals and mining wastes using hyperaccumulator plants to purposely bio-concentrate high levels of metals or...     

Site-specific PEGylation of protein disulfide bonds using a three-carbon bridge

The covalent conjugation of a functionalized poly(ethylene glycol) (PEG) to multiple nucleophilic amine residues results in a heterogeneous mixture of PEG positional isomers. Their physicochemical, biological, and pharmaceutical properties vary with the site of conjugation of PEG. Yields are low because of inefficient conjugation chemistry and production costs high because of complex purification procedures. Our solution to these fundamental problems in PEGylating proteins has been to exploit the latent conjugation selectivity of the two sulfur atoms that are derived from the ubiquitous disulfide bonds of proteins. This approach to PEGylation involves two steps: (1) disulfide reduction to release the two cysteine thiols and (2) re-forming the disulfide by bis-alkylation via a three-carbon bridge to which PEG was covalently attached. During this process, irreversible denaturation of the protein did not occur. Mechanistically, the conjugation is conducted by a sequential, interactive bis-alkylation using alpha,beta-unsaturated beta'-monosulfone functionalized PEG reagents. The combination of (a) maintaining the protein's tertiary structure after disulfide reduction, (b) the mechanism for bis-thiol selectivity of the PEG reagent, and (c) the steric shielding of PEG ensure that only one PEG molecule is conjugated at each disulfide bond. PEG was site-specifically conjugated via a three-carbon bridge to 2 equiv of the tripeptide glutathione, the cyclic peptide hormone somatostatin, the tetrameric protein l-asparaginase, and to the disulfides in interferon alpha-2b (IFN). SDS-PAGE, mass spectral, and NMR analyses were used to confirm conjugation, thiol selectivity, and connectivity. The biological activity of the l-asparaginase did not change after the attachment of four PEG molecules. In the case of IFN, a small reduction in biological activity was seen with the single-bridged IFN (without PEG attached). A significantly larger reduction in biological activity was seen with the three-carbon disulfide single-bridged PEG-IFNs and with the double-bridged IFN (without PEG attached). The reduction of the PEG-IFN's in vitro biological activity was a consequence of the steric shielding caused by PEG, and it was comparable to that seen with all other forms of PEG-IFNs reported. However, when a three-carbon bridge was used to attach PEG, our PEG-IFN's biological activity was found to be independent of the length of the PEG. This property has not previously been described for PEG-IFNs. Our studies therefore suggest that peptides, proteins, enzymes, and antibody fragments can be site-specifically PEGylated across a native disulfide bond using three-carbon bridges without destroying their tertiary structure or abolishing their biological activity. The stoichiometric efficiency of this approach also enables recycling of any unreacted protein. It therefore offers the potential to make PEGylated biopharmaceuticals as cost-effective medicines for global use.     

The role of the Parkinson's disease gene PARK9 in essential cellular pathways and the manganese homeostasis network in yeast

YPK9 (Yeast PARK9; also known as YOR291W) is a non-essential yeast gene predicted by sequence to encode a transmembrane P-type transport ATPase. However, its substrate specificity is unknown. Mutations in the human homolog of YPK9, ATP13A2/PARK9, have been linked to genetic forms of early onset parkinsonism. We previously described a strong genetic interaction between Ypk9 and another Parkinson's disease (PD) protein α-synuclein in multiple model systems, and a role for Ypk9 in manganese detoxification in yeast. In humans, environmental exposure to toxic levels of manganese causes a syndrome similar to PD and is thus an environmental risk factor for the disease. How manganese contributes to neurodegeneration is poorly understood. Here we describe multiple genome-wide screens in yeast aimed at defining the cellular function of Ypk9 and the mechanisms by which it protects cells from manganese toxicity. In physiological conditions, we found that Ypk9 genetically interacts with essential genes involved in cellular trafficking and the cell cycle. Deletion of Ypk9 sensitizes yeast cells to exposure to excess manganese. Using a library of non-essential gene deletions, we screened for additional genes involved in tolerance to excess manganese exposure, discovering several novel pathways involved in manganese homeostasis. We defined the dependence of the deletion strain phenotypes in the presence of manganese on Ypk9, and found that Ypk9 deletion modifies the manganese tolerance of only a subset of strains. These results confirm a role for Ypk9 in manganese homeostasis and illuminates cellular pathways and biological processes in which Ypk9 likely functions.     

Effect of Sodium Chloride and pH on Enterotoxin C Production

Growth and production of enterotoxin C by Staphylococcus aureus strain 137 in 3% + 3% protein hydrolysate powder N-Z Amine NAK broths with 0 to 12% NaCl and an initial pH of 4.00 to 9.83 were studied during an 8-day incubation period at 37 C. Growth was initiated at pH values as low as 4.00 and as high as 9.83 at 0% salt level as long as the inoculum contained at least 10(8) cells per ml. Rate of growth decreased as the NaCl concentration was increased gradually to 12%. Enterotoxin C was produced in broths inoculated with 10(8) cells per ml and above and having initial pH ranges of 4.00 to 9.83, 4.40 to 9.43, 4.50 to 8.55 and respective NaCl concentrations of 0, 4, and 8%. In the presence of 10% NaCl, the pH range supporting enterotoxin C production was 5.45 to 7.30 for an inoculum level of 10(8) cells per ml and 6.38 to 7.30 for 3.6 x 10(6) cells per ml. In repeated experiments in which the inoculum contained 10(8) cells per ml, we failed to demonstrate enterotoxin C production in broths with 12% NaCl and a pH range of 4.50 to 8.55 and concentrated up to 14 times. The effect of NaCl on enterotoxin C production followed the same pattern as its effect on enterotoxin B production. As the concentration of NaCl increased from 0 to 10%, yields of enterotoxin B and C decreased to undetectable amounts.     

Phospholipase C-dependent Ca2+ release by worm and mammal sperm factors

Egg activation in all animals evidently requires the synthesis of inositol 1,4,5-trisphosphate (InsP(3)) from phosphatidylinositol 4,5-bisphosphate (PIP(2)) by phospholipase C (PLC). Depending on the organism, InsP(3) elicits either calcium oscillations or a single wave, which in turn initiates development. A soluble component in boar sperm that activates mammalian eggs has been suggested to be a PLC isoform. We tested this hypothesis in vitro using egg microsomes of Chaetopterus. Boar sperm factor elicited Ca(2+) release from the microsomes by an InsP(3)-dependent mechanism. The PLC inhibitor U-73122, but not its inactive analog U-73343, blocked the response to sperm factor but not to InsP(3). U-73122 also inhibited the activation of fertilized and parthenogenetic eggs. Chaetopterus sperm also contained a similar activity. These results strongly support the hypothesis that sperm PLCs are ubiquitous mediators of egg activation at fertilization.     

Epidermal growth factor receptor: mechanisms of activation and signalling

The epidermal growth factor (EGF) receptor (EGFR) is one of four homologous transmembrane proteins that mediate the actions of a family of growth factors including EGF, transforming growth factor-alpha, and the neuregulins. We review the structure and function of the EGFR, from ligand binding to the initiation of intracellular signalling pathways that lead to changes in the biochemical state of the cell. The recent crystal structures of different domains from several members of the EGFR family have challenged our concepts of these processes.     

Structure and ligand binding of carbohydrate-binding module CsCBM6-3 reveals similarities with fucose-specific lectins and "galactose-binding" domains

Carbohydrate-binding polypeptides, including carbohydrate-binding modules (CBMs) from polysaccharidases, and lectins, are widespread in nature. Whilst CBMs are classically considered distinct from lectins, in that they are found appended to polysaccharide-degrading enzymes, this distinction is blurring. The crystal structure of CsCBM6-3, a "sequence-family 6" CBM in a xylanase from Clostridium stercorarium, at 2.3 A reveals a similar, all beta-sheet fold to that from MvX56, a module found in a family 33 glycoside hydrolase sialidase from Micromonospora viridifaciens, and the lectin AAA from Anguilla anguilla. Sequence analysis leads to the classification of MvX56 and AAA into a family distinct from that containing CsCBM6-3. Whilst these polypeptides are similar in structure they have quite different carbohydrate-binding specificities. AAA is known to bind fucose; CsCBM6-3 binds cellulose, xylan and other beta-glucans. Here we demonstrate that MvX56 binds galactose, lactose and sialic acid. Crystal structures of CsCBM6-3 in complex with xylotriose, cellobiose, and laminaribiose, 2.0 A, 1.35 A, and 1.0 A resolution, respectively, reveal that the binding site of CsCBM6-3 resides on the same polypeptide face as for MvX56 and AAA. Subtle differences in the ligand-binding surface give rise to the different specificities and biological activities, further blurring the distinction between classical lectins and CBMs.