Protein and Peptide Letters - Volume 10, Issue 3, 2003

This article is an overview of antimicrobial peptides found in anurans skin secretions. These molecules constitute an initial barrier against microbial infections because of their activity against a large array of microorganisms. These peptides hold remarkable pharmaceutical and technological interest since they selectively kill microorganisms and are unlikely to induce resistance in pathogens. Also, outstanding synergism occurs when these peptides are combined with classic antibiotics and other antimicrobial peptides.

Regardless of the differences in primary amino acid sequences, protein molecules in a number of conformational states behave as polymer homologues, allowing speculations as to the volume interactions being a driving force in formation of equilibrium structures. For instance, both native and molten globules exhibit key features of polymer globules, where the fluctuations of the molecular density are expected to be much less than the molecular density itself. Protein molecules in the compact denatured (pre-molten globule) states possess properties of squeezed coils. In fact, even high concentrations of strong denaturants (e.g., urea and GdmCl) more likely constitute bad solvents for protein chains. Thus, globular proteins are probably never random coils without positional correlations and biological polypeptide chains represent the macromolecular coils below a critical point even under harsh denaturing conditions. Several implications of these findings to protein folding are discussed.

The ability of succinate-cytochrome c reductase (SCR) reduced cytochrome c to scavenge H2O2 was investigated. H2O2, whether added or produced by SCR, was efficiently removed when cytochrome c was reduced by SCR. On the other hand, ferrocytochrome c underwent re-oxidization when H2O2 was added. Thus, these results indicate that cytochrome c reduced by succinate-cytochrome c reductase has the ability to regulate H2O2 in mitochondria.

Tabtoxin resistance protein (TTR) is an enzyme that catalyzes the acetylation of tabtoxin rendering tabtoxin-producing pathogens tolerant to their own phytotoxins. According to the structure based detoxification mechanism of TTR, three site-directed mutants Y141F, D130N and Y141F-D130N were constructed and overexpressed in E. coli. The products were then purified and their properties were analyzed by CD and DLS. Crystallization trials of two mutants Y141F andY141F-D130N were preformed.

Galectin-1 requires a reducing environment for its lectin activity and the carbohydrate binding function is destroyed in oxidizing condition. In this report we provide direct evidence that the oxidation of goat hepatic galectin-1 perturbs its carbohydrate recognition domain and this could be due to changes in secondary structure of goat hepatic galectin-1. Conformational changes in goat hepatic galectin-1 due to oxidation were investigated by absorption, fluorescence and circular dichroism measurements.

It is found that the helix parameter (HP), which favors clustering of non-polar residues, is linearly correlated with the logarithms of rate constants of folding of small two-state α-helical proteins. The definition is HP = NH-1 Σ [fi+ (fi-1+fi+1) / 2], where fi=1 or -1, if the i'th residue is hydrophobic or hydrophilic, respectively, NH is the number of hydrophobic residues and the summation is taken over the hydrophobic residues.

The HMG domain is a DNA binding and bending ‘architectural’ motif involved in chromatin re-modelling during transcription. Recombinant SRY HMG domain protein, 88 amino acids in length, has been produced in E. coli. Using FPLC and a stirred ultra-filtration cell, this domain has been purified to homogeneity and concentrated to yield milligram quantities. Functional characterisation studies of the pure, concentrated SRY HMG domain show the recombinantly expressed protein to be active in terms of DNA binding and calmodulin binding activities.

A new acidic lectin from red elder (Sambucus racemosa L.) bark has been isolated by affinity chromatography and gel filtration. Noteworthy, and in contrast to other Sambucus species, red elder bark lacks acidic non-toxic type 2 ribosome-inactivating proteins but has basic ribosome-inactivating protein activities. The new lectin (SRLbm) shows specificity for N-Ac-Galactosamine / D-Galactose and has an apparent Mr of 30,000. The N-terminal amino acid sequence displays a close homology with other lectins and B chains of non-toxic type 2 ribosome-inactivating proteins nigrins and ebulins present in other Sambucus species. SRLbm triggers red blood cell agglutination in the range 4-12 μg/ml.

The neurohypophyseal nonapeptide hormone oxytocin (OT) is the strongest uterotonic substance known and is responsible for the initiation of labor. Conversely, oxytocin antagonists blocking uterine OT receptor can suppress uterus contraction. In this paper we describe a computer simulated docking pertinent to affinity of an oxytocin antagonist atosiban towards OT receptor, versus vasopressin V1a and V2 receptors.

We report that the plant oncoprotein RolA from Agrobacterium rhizogenes acts to stabilize β- glucoronidase (Gus) when the two proteins are expressed as a fusion protein in transformed tobacco. The observed 50-fold increase of Gus activity was shown to be related to protein accumulation, with no significant changes in mRNA abundance, kinetic properties of the enzyme and thermostability. The entire RolA sequence is essential to achieve the full effect since both the N-terminal region, spanning a putative reverse signal-anchor and nuclear targeting sequences, or the contiguous C-terminal portion were shown to increase Gus activity only 10-fold. A possible interference of RolA in the protein degradation pathway regulated by auxin is discussed.

Osteoporosis influences the health of the females who are in menopause phase. The techniques to detect the markers of bone turnover is very important for preventing osteoporosis. ELISA was developed for detection of urinary N-telopeptide (NTx) as an osteoporosis marker. Our aim is to develop a sensitive method to detect NTx excretion using surface plasmon resonance (SPR). Samples collected were assayed and results suggest that our SPR-based method is promising for monitoring bone loss.

Ellman's method was used to determine the Michaelis-Menten parameters for the hydrolysis of acetylthiocholine by Electrophorus electricus acetylcholinesterase from 12 to 37°C. Arrhenius analysis revealed that the activation energy for formation of the enzyme / substrate complex is 22.2 ± 1.1 kJ / mole. The Arrhenius plot of kcat is markedly curved and attributed to comparable rates of acylation and deacylation due to the absence of evidence for a temperature-dependent enzyme conformational change by differential scanning calorimetry.

CbnR, a LysR-type transcriptional regulator from Ralstonia eutropha NH9, has been crystallized by the vapor-diffusion method. It is intriguing to note that the different mixing ratios between the protein and reservoir solutions resulted in the different crystal forms. These crystals have the symmetry of the orthorhombic system with space groups P21212 and P2 1 2 1 2 1.