Determining the CD spectrum of a protein

This unit describes the theory behind circular dichroism (CD) and deals with considerations regarding instrumentation and reagents for CD spectrometry. A protocol is provided that outlines the steps in recording a CD spectrum and two support protocols explain the interpretation of near-UV and far-UV CD spectra.

Presence of the propeptide on recombinant lysosomal dipeptidase controls both activation and dimerization

Lysosomal dipeptidase catalyzes the hydrolysis of dipeptides with unsubstituted terminals. It is a homodimer and binds zinc. Dimerization is an important issue in understanding the enzyme's function. In this study, we investigated the influence of the propeptide on the folding and dimerization of recombinant lysosomal dipeptidase. For this purpose, we separately cloned and overexpressed the mature protein and the proenzyme. The overexpressed proteins were localized exclusively to insoluble inclusion bodies. Refolding of the urea-solubilized inclusion bodies showed that only dipeptidase lacking the propeptide was dimeric. The soluble renatured proenzyme was a monomer, although circular dichroism and fluorescence spectra of the proenzyme indicated the formation of secondary and tertiary structure. The propeptide thus controls dimerization, as well as activation, of lysosomal dipeptidase.

In vitro study of the effectiveness of different dressings for debriding fibrin in blood clots from horses

Franz diffusion cells containing uniformly dehydrated equine blood clots to simulate fibrinous eschar were used to measure the rate of debridement of fibrin by novel and traditional wound dressings, under standardised conditions of temperature, pH and humidity. Significant increases in protein breakdown occurred within 24 hours with all the dressings, but not thereafter. In general, dressings hydrated in normal saline were better as debriding agents than dressings hydrated in water. Autolytic debriding agents were 47 per cent more effective than chemical debriding agents; specifically, hydrofibre and gauze dressings hydrated in saline broke down more than 3500 microg/ml of protein whereas dressings impregnated with proteolytic enzymatic agents digested less than 1400 microg/ml.

Structural characterization of thyroglobulin type-1 domains of equistatin

Equistatin is a protein composed of three thyroglobulin type-1 domains. It inhibits papain-like cysteine proteinases and the aspartic proteinase, cathepsin D. To determine the structural basis for this inhibition we cloned and expressed the separated domains (eq d-1, eq d-2, eq d-3) in Pichia pastoris. Kinetic constants for the interaction of eq d-1 with papain and that of eq d-2 with cathepsin D are of similar order (subnanomolar) and are comparable to the constants obtained for full-length equistatin. The target proteinase for the third domain remains unknown. Thus, we demonstrate here that thyroglobulin type-1 motifs per se are able to support specific structural features that enable them to inhibit proteases from different classes. The overall conformation of three domains in equistatin is such that the interaction of domains 1 or 2 with their respective target enzymes is not hindered sterically by either domain. In addition, we show that the interaction of eq d-2 with cathepsin D results in conformational changes, which is not the case for the eq d-1/papain interaction.

Geographies of infant feeding and access to primary health-care

Although the benefits of breastfeeding to mother and infant are now well established, within Britain initiation rates are low and have changed little since 1980. This is despite many health promotion initiatives aiming to increase breastfeeding. In this paper we discuss some of the findings of an exploratory qualitative research study of infant feeding decisions in Newcastle upon Tyne, England, where health professionals are actively seeking to increase local breastfeeding initiation and duration rates. Our findings suggest that for health promotion initiatives to be effective across all social groups, there needs to be (i) a socio-cultural understanding of different social groups' access to and interpretation of pre- and postnatal formal breastfeeding support health services, and (ii) more appreciation of how mothers' informal support networks impact on their access to, interpretation and use of formal breastfeeding support.

The slow step of folding of Staphylococcus aureus PC1 beta-lactamase involves the collapse of a surface loop rate limited by the trans to cis isomerization of a non-proline peptide bond

We wished to test the hypothesis that the non proline cis to trans isomerization of the peptide bond at position 167 in the S. aureus beta-lactamase PC1 exerts a significant controlling effect on the folding pathway of this enzyme. The previous data presented in support of this hypothesis could not rule out the effect of factors unrelated to non-proline cis/trans isomerization. We have used the plasmid pET9d to direct soluble overproduction of the S. aureus beta-lactamase PC1 and a site-directed mutant (Ile 167 to Pro) in Escherichia coli. Following purification the proteins were subjected to a comparative analysis of the kinetics of unfolding and refolding using the techniques of near- and far-UV circular dichroism spectroscopy and fluorescence spectroscopy in conjunction with "double-jump" experiments. Results show that the fully-unfolded I167P mutant enzyme retains 20% of molecules in a fast-refolding form and that slower-refolding molecules fold faster than the recombinant wild-type enzyme. The final stage of folding involves folding of the omega-loop into a conformation essential for enzymatic activity. In support of the original hypothesis, the folding of this omega-loop is rate limited by the isomerization of the Glu 166-Ile 167 peptide bond.

Mode of action of carbimazole in Graves' disease

In a series of hyperthyroid subjects treated with a high dose 'block-replace' regime, mean thyroidal technetium uptake was shown to fall progressively over an 18 month period. Furthermore, sub-total inhibition of hormone biosynthesis could be demonstrated, without evidence of proportionate inhibition of organification, the regression of radio-iodine on technetium thyroid uptake showing similar slopes in euthyroid, treated and untreated hyperthyroid subjects. Together with the reported differential in remission rates between propranolol and anti-thyroid drugs, it is concluded that carbimazole does not act solely by inhibiting intrathyroid hormono-genesis, but more definitively by affecting thyroid hyperstimulation at a pre-biosynthetic level. The inability to demonstrate normal suppressibility of trapping in any subject in the present series despite extended therapy with a 'block-replace' regime, further suggests that current concepts of 'suppressibility' are invalid, the progressive fall in technetium uptake being unlikely to represent spontaneous restoration of a normal pituitary-thyroid axis, but rather a direct influence or prolonged therapy with anti-thyroid drugs on the natural history of the disease.