Golgins in the structure and dynamics of the Golgi apparatus.

Golgins are a family of coiled-coil proteins associated with the Golgi apparatus necessary for tethering events in membrane fusion and as structural supports for Golgi cisternae. Recent work has shown that golgins such as GM130, golgin-45 and p115 bind to Rab GTPases via their coiled-coil domains, and that GM130, rather than being part of a static structural matrix, is in dynamic exchange between the membrane surface and the cytoplasm. Golgins such as bicaudal-D1 and -D2 bind to Rab6, but, rather than tethering membranes together, link vesicles to the cytoskeleton, thus adding a new function for this class of proteins. Other golgins containing the Golgi targeting GRIP domain, rather than binding Rabs, interact with and are recruited to membranes by another class of GTPase, the Arls. Current evidence therefore suggests that golgins function in a variety of membrane-membrane and membrane-cytoskeleton tethering events at the Golgi apparatus, and that all these are regulated by small GTPases of the Rab and Arl families.

YSK1 is activated by the Golgi matrix protein GM130 and plays a role in cell migration through its substrate 14-3-3zeta.

The Golgi apparatus has long been suggested to be important for directing secretion to specific sites on the plasma membrane in response to extracellular signaling events. However, the mechanisms by which signaling events are coordinated with Golgi apparatus function remain poorly understood. Here, we identify a scaffolding function for the Golgi matrix protein GM130 that sheds light on how such signaling events may be regulated. We show that the mammalian Ste20 kinases YSK1 and MST4 target to the Golgi apparatus via the Golgi matrix protein GM130. In addition, GM130 binding activates these kinases by promoting autophosphorylation of a conserved threonine within the T-loop. Interference with YSK1 function perturbs perinuclear Golgi organization, cell migration, and invasion into type I collagen. A biochemical screen identifies 14-3-3zeta as a specific substrate for YSK1 that localizes to the Golgi apparatus, and potentially links YSK1 signaling at the Golgi apparatus with protein transport events, cell adhesion, and polarity complexes important for cell migration.

Culture, executive function, and social understanding.

Much of the evidence from the West has shown links between children's developing self-control (executive function), their social experiences, and their social understanding (Carpendale & Lewis, 2006, chapters 5 and 6), across a range of cultures including China. This chapter describes four studies conducted in three Oriental cultures, suggesting that the relationships among social interaction, executive function, and social understanding are different in these cultures, implying that social and executive skills are underpinned by key cultural processes.

Membrane fusion: caught in a trap.

SNAREs are small coiled-coil proteins required for specific membrane fusion events in eukaryotic cells. Recent evidence points to the existence of an inhibitory class of SNAREs, i-SNAREs, which prevent incorrect fusions from occurring, adding a further layer of regulation to the process of membrane docking and fusion.

Membrane traffic: a glitch in the Golgi matrix.

Golgins are coiled-coil proteins thought to form a matrix important for shaping and organising Golgi cisternae and directing long-range recognition events in vesicular transport. This model is brought into question by new evidence that two golgins, GM130 and golgin-84, contribute to but are not essential for protein transport and Golgi structure.

The Rab6 GTPase regulates recruitment of the dynactin complex to Golgi membranes.

Dynactin is a multisubunit protein complex required for the activity of dynein in diverse intracellular motility processes, including membrane transport. Dynactin can bind to vesicles and liposomes containing acidic phospholipids, but general properties such as this are unlikely to explain the regulated recruitment of dynactin to specific sites on organelle membranes. Additional factors must therefore exist to control this process. Candidates for these factors are the Rab GTPases, which function in the tethering of vesicles to their target organelle prior to membrane fusion. In particular, Rab27a tethers melanosomes to the actin cytoskeleton. Other Rabs have been implicated in microtubule-dependent organelle motility; Rab7 controls lysosomal transport, and Rab6 is involved in microtubule-dependent transport pathways through the Golgi and from endosomes to the Golgi. We demonstrate that dynactin binds to Rab6 and shows a Rab6-dependent recruitment to Golgi membranes. Other Golgi Rabs do not bind to dynactin and are unable to support its recruitment to membranes. Rab6 therefore functions as a specificity or tethering factor controlling the recruitment of dynactin to membranes.

Phosphatidylinositol-5-phosphate activation and conserved substrate specificity of the myotubularin phosphatidylinositol 3-phosphatases.

Phosphoinositides control many different processes required for normal cellular function. Myotubularins are a family of Phosphatidylinositol 3-phosphate (PtdIns3P) phosphatases identified by the positional cloning of the MTM1 gene in patients suffering from X-linked myotubular myopathy and the MTMR2 gene in patients suffering from the demyelinating neuropathy Charcot-Marie-Tooth disease type 4B. MTM1 is a phosphatidylinositol phosphatase with reported specificity toward PtdIns3P, while the related proteins MTMR2 and MTMR3 hydrolyze both PtdIns3P and PtdIns(3,5)P2. We have investigated MTM1 and MTMR6 and find that they use PtdIns(3,5)P2 in addition to PtdIns3P as a substrate in vitro. The product of PtdIns(3,5)P2 hydrolysis, PtdIns5P, causes MTM1 to form a heptameric ring that is 12.5 nm in diameter, and it is a specific allosteric activator of MTM1, MTMR3, and MTMR6. A disease-causing mutation at arginine 69 of MTM1 falling within a putative pleckstrin homology domain reduces the ability of the enzyme to respond to PtdIns5P. We propose that the myotubularin family of enzymes utilize both PtdIns3P and PtdIns(3,5)P2 as substrates, and that PtdIns5P functions in a positive feedback loop controlling their activity. These findings highlight the importance of regulated phosphatase activity for the control of phosphoinositide metabolism.

Golgins and GTPases, giving identity and structure to the Golgi apparatus.

In this review we will focus on the recent advances in how coiled-coil proteins of the golgin family give identity and structure to the Golgi apparatus in animal cells. A number of recent studies reveal a common theme for the targeting of golgins containing the ARL-binding GRIP domain, and the related ARF-binding GRAB domain. Similarly, other golgins such as the vesicle tethering factor p115 and Bicaudal-D are targeted by the Rab GTPases, Rab1 and Rab6, respectively. Together golgins and their regulatory GTPases form a complex network, commonly known as the Golgi matrix, which organizes Golgi membranes and regulates membrane trafficking.

Assay and properties of rab6 interaction with dynein-dynactin complexes.

RAB GTPases help to maintain the fidelity of membrane trafficking events by recruiting cytosolic tethering and motility factors to vesicle and organelle membranes. In the case of Rab6, it recruits the dynein-dynaction complex to Golgi-associated vesicles via an adaptor protein of the Bicaudal-D family. Here we describe methods for the identification of Rab6-binding partners in cell extracts. We then focus on the biochemical analysis of interactions with the dynein-dynactin complex and the adaptor proteins Bicaudal-D1 and -D2. Standard protocols for yeast two-hybrid analysis, and biochemical assays for the analysis of the interactions between Rab6, Bicaudal-D, and the subunits of the dynein-dynactin complex are outlined.

Evaluation of molecular typing methods in characterizing a European collection of epidemic methicillin-resistant Staphylococcus aureus strains: the HARMONY collection.

We analyzed a representative sample of methicillin-resistant Staphylococcus aureus (MRSA) from 11 European countries (referred to as the HARMONY collection) using three molecular typing methods used within the HARMONY group to examine their usefulness for large, multicenter MRSA surveillance networks that use these different laboratory methodologies. MRSA isolates were collected based on their prevalence in each center and their genetic diversity, assessed by pulsed-field gel electrophoresis (PFGE). PFGE groupings (< or = 3 bands difference between patterns) were compared to those made by sequencing of the variable repeats in the protein A gene spa and clonal designations based on multilocus sequence typing (MLST), combined with PCR analysis of the staphylococcal chromosome cassette containing the mec genes involved in methicillin resistance (SCCmec). A high level of discrimination was achieved using each of the three methodologies, with discriminatory indices between 89.5% and 91.9% with overlapping 95% confidence intervals. There was also a high level of concordance of groupings made using each method. MLST/SCCmec typing distinguished 10 groups containing at least two isolates, and these correspond to the majority of nosocomial MRSA clones described in the literature. PFGE and spa typing resolved 34 and 31 subtypes, respectively, within these 10 MRSA clones, with each subtype differing only slightly from the most common pattern using each method. The HARMONY group has found that the methods used in this study differ in their availability and affordability to European centers involved in MRSA surveillance. Here, we demonstrate that the integration of such technologies is achievable, although common protocols (such as we have developed for PFGE) may also be important, as is the use of centralized Internet sites to facilitate data analysis. PFGE and spa-typing data from analysis of MRSA isolates from the many centers that have access to the relevant equipment can be compared to reference patterns/sequences, and clonal designations can be made. In the majority of cases, these will correspond to those made by the (more expensive) method of choice-MLST/SCCmec typing-and these alternative methods can therefore be used as frontline typing systems for multicenter surveillance of MRSA.

In vitro activity of a novel compound, the metal ion chelating agent AQ+, against clinical isolates of Staphylococcus aureus.

OBJECTIVES: To determine the efficacy of a novel antimicrobial compound, AQ+, against a genetically heterogeneous collection comprising 213 Staphylococcus aureus isolates from global sources. AQ+ is an aqueous preparation containing 0.5% 8-hydroxyquinoline. METHODS: MICs were found for all the isolates tested using the BSAC microdilution method. Time-kill studies were performed according to NCCLS guidelines. Transmission electron microscopy (TEM) was used to view the ultrastructural effects of AQ+. RESULTS: AQ+ was shown to strongly inhibit the growth of all isolates with a median MIC of 0.25% at a pH optimum of 9.2. Lowering the pH to 7.5 gave an approximately 4-fold reduction in efficacy and at pH 5.5 there was an approximately 8-fold reduction in efficacy. Methicillin-resistant S. aureus (MRSA) as well as vancomycin-intermediate S. aureus were shown to be as equally susceptible to AQ+ as methicillin-susceptible S. aureus. Time-kill curves for AQ+ were similar to those for gentamicin. TEM showed that AQ+ actively disrupts the cell wall of S. aureus leading to cell lysis. CONCLUSIONS: These results suggest that AQ+ has strong antimicrobial activity and may be useful in preparations to reduce nasal and skin carriage of MRSA.