Real-time scanning tunnelling microscopy imaging of protein motion at electrode surfaces

A mutant (K27C) of the blue copper protein azurin [Eur. J. Biochem. 194 (1990) 109; J. Mol. Biol. 221 (1991) 765] for orientated immobilisation on gold surfaces was analysed by scanning tunnelling microscopy (STM) both in a resting state and following the application of a short potential pulse between the tip and sample.

Introduction of a (poly)histidine tag in L-lactate dehydrogenase produces a mixture of active and inactive molecules

A (poly)histidine tag was fused to either the N- or the C-terminus of L-lactate dehydrogenase (LDH) of Bacillus stearothermophilus to facilitate purification and immobilization of these enzymes. The C-terminally tagged enzyme displayed lower activity compared both to the wild-type and to the N-terminally tagged variant. The reason for this loss of activity was investigated by affinity chromatography of the enzymes on a 5'-AMP-Sepharose resin and by size-exclusion chromatography. The C-terminally tagged enzyme could be separated into an inactive, unbound fraction and an active, bound fraction. Further differences between the C-terminally tagged enzyme and the N-terminally tagged and wild-type LDH were observed on size-exclusion chromatography of the three enzymes. These data suggest that the introduction of a "his-tag" at the C-terminus may induce misfolding of the LDH and serve as a warning that the introduction of a (poly)histidine tag can produce unforseen changes in a protein.

A factorial analysis of silanization conditions for the immobilization of oligonucleotides on glass surfaces

The modification of glass surfaces with (3-mercaptopropyl)trimethoxysilane and the application of this to DNA chip technology are described. A range of factors influencing the silanization method, and hence the number of surface-bound, chemically active thiol groups, were investigated using a design of experiment approach based on analysis of variance. The number of thiol groups introduced on glass substrates were measured directly using a specific radiolabel, [14C]cysteamine hydrochloride. For liquid-phase silanization, the number of surface-bound thiol groups was found to be dependent on both postsilanization thermal curing and silanization time and relatively independent of silane concentration, reaction temperature, and sample pretreatment. Depending on the conditions used in liquid-phase silanization, (1.3-9.0) x 10(12) thiol groups/cm2 on the glass samples were bound. The reliability and repeatability of liquid- and vacuum-phase silanization were also investigated. Eighteen-base oligonucleotide probes were covalently attached to the modified surfaces via a 3'-amino modification on the DNA and subsequent reaction with the cross-linking reagent N-(gamma-maleimidobutyryloxy) succinimide ester (GMBS). The resulting probe levels were determined and found to be stoichiometric with that of the introduced thiol groups. These results demonstrate that silanization of glass surfaces under specific conditions, prior to probe attachment, is of great importance in the development of DNA chips that use the simple concept of the covalent attachment of presynthesized oligonucleotides to silicon oxide surfaces.

Site-specific introduction of an electroactive label into a non-electroactive enzyme (beta-lactamase I)

A cysteine residue was introduced close to the active site of beta-lactamase I by site-directed mutagenesis to replace tyrosine-105 and was subsequently modified with an electroactive SH-specific reagent, N-(2-ferrocene-ethyl)maleimide. The resulting modified enzyme became electroactive, showing good quasireversible electrochemistry which was characteristic of the attached ferrocene moiety while retaining its specific enzymatic activity. In the presence of a suicide substrate, 6beta-iodopenicillanic acid, the redox potential shifted +20 mV suggesting that the label was sensitive to changes in the active site of the enzyme.

Radioactivity in two tide-washed marsh areas in the eastern Irish Sea: a radiological assessment

The doses received by man from exposure to artificial radionuclides deposited onto marsh land during tidal inundation on the English side of the Solway Firth and the Dee Estuary have been assessed. The range of total doses received by the different marsh user groups was similar in both study areas, varying from < 1 microSv year-1 to approximately 55 microSv year-1, with total dose dominated by the contribution from external exposure (generally 80% of the total). The maximum doses in both study areas were received by people working on the marshes and are well below the annual dose limit recommended by ICRP for members of the public (1 mSv year-1). The largest dose estimated (56 microSv year-1) is only 6% of the recommended dose limit.