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S Munro

Publications and source records attributed to S Munro.

At least 37 records · Page 2Linked to original sources
PubMed1998

A common motif of eukaryotic glycosyltransferases is essential for the enzyme activity of large clostridial cytotoxins.

A fragment of the N-terminal 546 amino acid residues of Clostridium sordellii lethal toxin possesses full enzyme activity and glucosylates Rho and Ras GTPases in vitro. Here we identified several amino acid residues in C. sordellii lethal toxin that are essential for the enzyme activity of the active toxin fragment. Exchange of aspartic acid at position 286 or 288 with alanine or asparagine decreased glucosyltransferase activity by about 5000-fold and completely blocked glucohydrolase activity. No enzyme activity was detected with the double mutant D286A/D288A. Whereas the wild-type fragment of C. sordellii lethal toxin was labeled by azido-UDP-glucose after UV irradiation, mutation of the DXD motif prevented radiolabeling. At high concentrations (10 mM) of manganese ions, the transferase activities of the D286A and D288A mutants but not that of wild-type fragment were increased by about 20-fold. The exchange of Asp270 and Arg273 reduced glucosyltransferase activity by about 200-fold and blocked glucohydrolase activity. The data indicate that the DXD motif, which is highly conserved in all large clostridial cytotoxins and also in a large number of glycosyltransferases, is functionally essential for the enzyme activity of the toxins and may participate in coordination of the divalent cation and/or in the binding of UDP-glucose.

Amino Acid Sequence↗
PubMed1998

Activity of the yeast MNN1 alpha-1,3-mannosyltransferase requires a motif conserved in many other families of glycosyltransferases.

A wide diversity of biological molecules are modified by the addition of sugar residues, and a large number of glycosyltransferases have been identified that are responsible for these reactions. Despite catalyzing closely related reactions, many of these transferases show little apparent sequence homology. By comparing two apparently unrelated families of yeast Golgi mannosyltransferases, a short motif containing two aspartate residues was observed that was conserved in both groups of proteins. Mutagenesis of one of the members of these families, the alpha-1, 3-mannosyltransferase Mnn1p, showed that altering either of these aspartates eliminates all enzymatic activity. These changes do not appear to affect the overall folding and assembly of Mnn1p. A similar aspartate-containing sequence was found to be conserved in a diverse range of other glycosyltransferase families, much more frequently than would be expected by chance, suggesting that it is a feature of the catalytic site, or an element of a structural fold, shared by many glycosyltransferases.

Amino Acid Sequence↗
PubMed1998

The pleckstrin homology domain of oxysterol-binding protein recognises a determinant specific to Golgi membranes.

BACKGROUND: Peripheral membrane proteins are targeted to the cytoplasmic face of specific intracellular membranes. The organelle-specific ligands recognised by peripheral proteins include other proteins and lipids. Oxysterol-binding protein (OSBP) translocates from the cytoplasm to the Golgi apparatus on binding oxygenated derivatives of cholesterol. The mechanism by which OSBP recognises the Golgi is unknown. It does, however, contain a pleckstrin homology (PH) domain, which in other proteins has been found to mediate regulated membrane binding, although in all previously studied examples the binding is to the plasma membrane. RESULTS: The PH domain of OSBP and of a yeast homologue, Osh1p, were sufficient to target proteins specifically to mammalian Golgi membranes. In addition, high level expression disrupted Golgi architecture and prevented forward traffic of cargo protein. In vitro, the OSBP PH domain bound to Golgi membranes in a manner apparently dependent on phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) or a related phosphatidylinositide. The OSBP PH domain bound to PI(4,5)P2 in liposomes with a submicromolar dissociation constant. CONCLUSIONS: The PH domains of OSBP and its yeast homologue recognise a determinant which is specific to Golgi membranes and important for Golgi function. The determinant appears to be a combination or a phosphatidylinositol polyphosphate and a second, Golgi-specific feature.

Animals↗
PubMed1998

Multi-protein complexes in the cis Golgi of Saccharomyces cerevisiae with alpha-1,6-mannosyltransferase activity.

Anp1p, Van1p and Mnn9p constitute a family of membrane proteins required for proper Golgi function in Saccharomyces cerevisiae. We demonstrate that these proteins colocalize within the cis Golgi, and that they are physically associated in two distinct complexes, both of which contain Mnn9p. Furthermore, we identify two new proteins in the Anp1p-Mnn9p-containing complex which have homology to known glycosyltransferases. Both protein complexes have alpha-1, 6-mannosyltransferase activity, forming a series of poly-mannose structures. These reaction products also contain some alpha-1, 2-linked mannose residues. Our data suggest that these two multi-protein complexes are responsible for the synthesis and initial branching of the long alpha-1,6-linked backbone of the hypermannose structure attached to many yeast glycoproteins.

Amino Acid Sequence↗
PubMed1998

Shared parenting: assessing the success of a foster parent program aimed at family reunification.

OBJECTIVE: There were two main objectives of the study: (1) To assess the effectiveness of a model of family reunification which united the role of parent aide and foster parent; and (2) to determine which characteristics of the families with children in care were associated with reunification. METHOD: A multisite project known as the Shared Parenting Project recruited families from five child protection agencies to participate in a program in which foster parents became extended rather than substitute families. Families were tested before the program began on a number of sociodemographic, psychological, and family measures. The success of the program was determined by whether the child was able to return home of if the program facilitated permanency planning. The success of the project was also examined by considering the relationship between returning home and a number of risk factors measured in the families with children in care. RESULTS: Very few families who met the criteria for the project could be recruited and only 31% of the participants completed the program and returned home. The process of permanency planning was facilitated in another 50% of the cases. The more stable families with less risk factors were more likely to complete the program successfully and to have their children return home. CONCLUSIONS: The results indicate that although the treatment model has excellent potential with less at-risk families it could not meet the treatment needs of the majority of families with children in foster care in the five child protection agencies. It is recommended that this model could be most helpful offered through parent aides attached to community support agencies that could provide respite care, support, and resources to families as needed thus avoiding the child having to be placed in care.

Adult↗
PubMed1998

Localization of proteins to the Golgi apparatus.

For the Golgi apparatus to perform its various unique roles it must maintain a population of resident proteins. These residents include the enzymes that modify the proteins and lipids passing through the Golgi, as well as the proteins involved in vesicle formation and protein sorting. For several of these residents, it has been possible to identify regions that are crucial for specifying a Golgi localization. Consideration of how these targeting domains could function has provided insights into the organization of the Golgi and its protein and lipid content.

Animals↗
PubMed1996

Intra-Golgi transport inhibition by megalomicin.

Megalomicin (MGM) is a macrolide antibiotic which has been demonstrated previously to cause an anomalous glycosylation of viral proteins. Here we show that MGM produces profound alterations on Golgi morphology and function. The addition of MGM at 50 microM for 1 h caused a dilation of the Golgi detected by immunofluorescence staining for medial- and trans-Golgi markers. The effect of MGM was clearly more intense on the trans-side of the Golgi, as evidenced in electron microscope preparations. The effect on Golgi morphology was reversible and correlated with an impairment of glycoprotein processing in the trans-Golgi. Thus, although the vesicular stomatitis virus G protein was processed in the presence of MGM to an endoglycosidase H-resistant form, it was poorly sialylated. The sialylation of cellular proteins was also inhibited, resulting in cells with low level of sialylation on the cell surface. However MGM did not inhibit the activities of the galactosyl- or sialyltransferase as measured in vitro. MGM inhibited cis- to medial-, and more strongly, medial- to trans-Golgi transport of vesicular stomatitis virus G protein in an in vitro system, suggesting that the impairment in glycoprotein maturation observed in vivo is the result of intra-Golgi transport inhibition.

Animals↗
PubMed1995

An investigation of the role of transmembrane domains in Golgi protein retention.

The single transmembrane domains (TMDs) of the resident glycosylation enzymes of the Golgi apparatus are involved in preventing these proteins moving beyond the Golgi. It has been proposed that either the TMDs associate, resulting in the formation of large oligomers of Golgi enzymes, or that they mediate the lateral segregation of the enzymes between lipid microdomains. Evidence for either type of interaction has been sought by examining the retention of sialyltransferase (ST), an enzyme of the mammalian trans Golgi. No evidence could be obtained for specific interactions or 'kin recognition' between ST and other proteins of the trans Golgi. Moreover, it is shown that the previously described kin recognition between enzymes of the medial Golgi involves the lumenal portions of these proteins rather than their TMDs. To investigate further the role of the ST TMD, the effects on Golgi retention of various alterations in the TMD were examined. The addition or removal of residues showed that the efficiency of retention of ST is related to TMD length. Moreover, when a type I plasma membrane protein was expressed with a synthetic TMD of 23 leucines it appeared on the cell surface, but when the TMD was shortened to 17 leucines accumulation in the Golgi was observed. These observations are more consistent with lipid-based sorting of ST TMD, but they also allow for reconciliation with the kin recognition model which appears to act on sequences outside of the TMD.

Amino Acid Sequence↗
PubMed1995

The use of Vicryl mesh (polyglactin 910) for implantation of hydroxyapatite orbital implants.

Hydroxyapatite (HA) implants currently are most commonly wrapped in donor sclera before implantation to facilitate placement within the orbit and allow attachment of the extraocular muscles. Although the risk of acquiring a transmittable disease through donor sclera is extremely low, some individuals remain concerned about receiving nonautologous material. As an alternative to sclera, autologous temporalis fascia, or autologous fascia lata, we have been wrapping HA in "Vicryl mesh" before insertion into the orbit. The Vicryl mesh-wrapped implant goes into the socket readily, allows one to easily attach the extraocular muscles, and has no risk of transmittable disease. In addition, the Vicryl mesh is readily available at most hospitals and is dissolvable.

Durapatite↗
PubMed1995

A comparison of the restraint and seclusion experiences of patients with schizophrenia or other psychotic disorders.

OBJECTIVE: The purpose of this study was to understand how restrained and secluded patients felt about these interventions, and to compare the perceptions of the two groups. METHODS: Subjects were 25 restrained, and 25 secluded inpatients. A questionnaire was developed to explore patients' feelings and perceptions of the two interventions. Comparisons were made on the clinical data and the answers from both groups. RESULTS: Restrained and secluded patients seemed to view some aspects of their experience differently. Few (40%) of the secluded group reported finding positive aspects, compared to even fewer (20%) of restrained. Most patients in both groups felt negatively about staff involved, and disagreed with staff on the reported intensity of their documented threatening behavior. The interventions seemed to have only a brief modifying effect on patients' behavior following these interventions and did not seem to modify future behavior. CONCLUSIONS: Despite their differences, many patients in both groups reported negative feelings about the interventions and the staff involved. Both groups seemed not to perceive the procedural staff interactions as communication. Our study population seemed to be a subgroup of the admitted patient population who were repeatedly requiring seclusion or restraint. Screening this patient population during the admission process, and planning preventive and alternative interventions could decrease the need for restraint and seclusion.

Adolescent↗
PubMed1994

Ocular findings in acromesomelic dysplasia.

We examined an infant who had prenatal onset of a skeletal dysplasia that had many features in common with acromesomelic dysplasia, including the clinical and light and electron microscopic findings of both corneas. Successful lamellar keratoplasty was performed on the left eye when histologic examination of the corneal button from the right eye showed that the corneal scar was only of partial thickness.

Cornea↗
PubMed1994

The functioning of the yeast Golgi apparatus requires an ER protein encoded by ANP1, a member of a new family of genes affecting the secretory pathway.

Mnt1p is an alpha 1.2-mannosyltransferase which resides in an early compartment of the Saccharomyces cerevisiae Golgi apparatus. We have shown that the signal-anchor region is sufficient, and the transmembrane domain necessary, for its normal Golgi localization. This is similar to the transmembrane domain-mediated retention of mammalian glycosyltransferases, and distinct from the tail-mediated recycling retention of certain mammalian and yeast trans-Golgi proteins. To examine the mechanism involved in transmembrane domain-mediated retention, we have isolated six classes of mutants which fail to retain Mnt1p-reporter fusions in the early Golgi. These mutants all show additional phenotypes which are consistent with alterations in Golgi function. We have called the mutant classes 'gem', for Golgi enzyme maintenance. GEM3 is identical to the previously cloned gene ANP1, and homologous to VAN1 and MNN9. Together, these define a new class of proteins involved in the organization and functioning of the secretory pathway. Interestingly, Anp1p is localized to the endoplasmic reticulum (ER), implying that some function of the ER is required to maintain a functional Golgi apparatus.

Amino Acid Sequence↗
PubMed1994

Retrieval of TGN proteins from the cell surface requires endosomal acidification.

TGN38 is a protein of unknown function located in the trans-Golgi network (TGN) of mammalian cells. Its intracellular distribution is maintained by it being continuously retrieved from the plasma membrane. In this paper we show that when cells are treated with agents such as chloroquine which neutralize acidic organelles, the movement of TGN38 along the endocytic pathway is blocked. The same effect is observed with a second TGN protein, the protease furin. We show that the cytoplasmic tail of furin is sufficient to confer a chloroquine-sensitive TGN localization on a heterologous protein. These results imply that the internal pH of endosomes affects sorting processes mediated by signals in the cytoplasmic portion of proteins and have implications for the role of acidification in endosomal function.

Acids↗