Biomedical subjects

Tanya E S Dahms

Publications and source records attributed to Tanya E S Dahms.

5 recordsLinked to original sources

PubMed2006

Fungal surface remodelling visualized by atomic force microscopy.

Most fungal growth is localized to the tips of hyphae, however, early stages of spore germination and the growth of certain morphological mutant strains exhibit non-polarized expansion. We used atomic force microscopy (AFM) to document changes in Aspergillus nidulans wall surfaces during non-polarized growth: spore germination, and growth in a strain containing the hypA1 temperature sensitive morphogenesis defect. We compared wall surface structures of both wild-type and mutant A. nidulans following growth at 28 degrees and 42 degrees C, the latter being the restrictive temperature for hypA1. There was no appreciable difference in surface ultrastructure between wild-type and hypA1 spores, or hyphal walls grown at 28 degrees C. When dry mature A. nidulans conidia were wetted they lost their hydrophobin coat, indicating an intermediate stage between dormancy and swelling. The surface structure of hypA1 germlings grown at 42 degrees C was less organized than wild-type hyphae grown under the same conditions, and had a larger range of subunit sizes. AFM images of hyphal wall surface changes following a shift in growth temperature from restrictive (42 degrees C) to permissive (28 degrees C), showed a gradient of sizes for wall surface features similar to the trend observed for wild-type cells at branch points. Changes associated with the hyphal wall structure for A. nidulans hypA1 offer insight into the events associated with fungal germination, and wall remodelling.

Aspergillus nidulans↗

PubMed2006

Electrostatic interactions of colicin E1 with the surface of Escherichia coli total lipid.

The surface properties of colicin E1, a 522-amino acid protein, and its interaction with monolayers of Escherichia coli (E. coli) total lipid and 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DOPC) were studied using the Langmuir-Blodgett (LB) technique. Colicin E1 is amphiphilic, forming a protein monolayer at the air/buffer interface. The protein is thought to interact with the E. coli total lipid head groups through electrostatic interactions, followed by its insertion into the lipid monolayers. Supported lipid bilayers (SLBs) of E. coli total lipid and DOPC, deposited onto mica at the cell membrane equivalence pressure for E. coli and incubated with colicin E1, were imaged by contact mode atomic force microscopy (CM-AFM). Colicin E1 formed protein aggregates on DOPC SLBs, while E. coli total lipid SLB was deformed following its incubation with colicin E1. Corresponding lateral force images, along with electrostatic surface potentials for colicin E1 P190, imply a direct interaction of colicin E1 with lipid head groups facilitating their charge neutralization.

Colicins↗

PubMed2005

The apo and ternary complex structures of a chemotherapeutic target: human glycinamide ribonucleotide transformylase.

Glycinamide ribonucleotide transformylase (GART; 10-formyltetrahydrofolate:5'-phosphoribosylglycinamide formyltransferase, EC 2.1.2.2), an essential enzyme in de novo purine biosynthesis, has been a chemotherapeutic target for several decades. The three-dimensional structure of the GART domain from the human trifunctional enzyme has been solved by X-ray crystallography. Models of the apoenzyme, and a ternary complex with the 10-formyl-5,8-dideazafolate cosubstrate and a glycinamide ribonucleotide analogue, hydroxyacetamide ribonucleotide [alpha,beta-N-(hydroxyacetyl)-d-ribofuranosylamine], are reported to 2.2 and 2.07 A, respectively. The model of the apoenzyme represents the first structure of GART, from any source, with a completely unoccupied substrate and cosubstrate site, while the ternary complex is the first structure of the human GART domain that is bound at both the substrate and cosubstrate sites. A comparison of the two models therefore reveals subtle structural differences that reflect substrate and cosubstrate binding effects and implies roles for the invariant residues Gly 133, Gly 146, and His 137. Preactivation of the DDF formyl group appears to be key for catalysis, and structural flexibility of the active end of the substrate may facilitate nucleophilic attack. A change in pH, rather than folate binding, correlates with movement of the folate binding loop, whereas the phosphate binding loop position does not vary with pH. The electrostatic surface potentials of the human GART domain and Escherichia coli enzyme explain differences in the binding affinity of polyglutamylated folates, and these differences have implications to future chemotherapeutic agent design.

Apoproteins↗

PubMed2005

Surface ultrastructure and elasticity in growing tips and mature regions of Aspergillus hyphae describe wall maturation.

This study reports the first direct, high-resolution physical and structural evidence of wall changes during hyphal tip growth, visualized by atomic force microscopy (AFM) in Aspergillus nidulans. Images from AFM and cryo-scanning electron microscopy provided comparable information, but AFM was also able to image and physically probe living cells. AFM images showed changes in the surface ultrastructure of A. nidulans hyphae, from newly deposited walls at hyphal tips to fully mature walls, as well as additional changes at young branches arising from mature walls. Surface architecture during wall maturation correlated with changes in the relative viscoelasticity (compliance per unit applied force) of walls measured by force spectroscopy (FS) in growing A. nidulans hyphae. Growing tips showed greater viscoelasticity than mature walls, despite equal support from turgor. Branch tips had comparable viscoelasticity to hyphal tips, unlike the mature wall from which they grew. FS also revealed differences in surface hydrophilicity between newly deposited and mature walls, with the tips being more hydrophilic. The hydrophilicity of young branch tips was similar to that of hyphal tips, and different from that of mature walls. Taken together, AFM images and FS data suggest that the A. nidulans wall matures following deposition at the hyphal tip.

Aspergillus nidulans↗

PubMed2002

Expression of the human mu opioid receptor in a stable Sf9 cell line.

The cDNA that encodes the human mu opioid receptor (hMOR) has been cloned and expressed in Spodoptera frugiperda (Sf9) cells using a nonlytic vector system. The coding sequence fused to the cleavable glycoprotein signal peptide gp 64, and a C-terminal histidine tag was placed under the transcriptional control of the Orgyia pseudotsugata multicapsid nucleopolyhedrosis virus immediate-early 2 (OpIE2) promoter. Transfected cells were selected using Zeocin resistance and the receptor was constitutively expressed at approximately 12000 receptors per cell. Immunofluorescence images illustrated that more than 75% of the Sf9 cells expressed hMOR at the plasma membrane. This is the first report of the constitutive and heterologous expression of a G protein-coupled receptor in a stably transfected Sf9 cell line, under the control of the OpIE2 promoter.

Animals↗