Identification of an aprotinin antiviral domain

Plasmid DNA nicking- a Novel Activity of Soybean Trypsin Inhibitor and Bovine Aprotinin

Protease inhibitors, such as trypsin inhibitor, serum alpha-1 antitrypsin, or liver aprotinin, are a class of proteins that competitively bind and block the catalytic activity of proteolytic enzymes with wide ranging biological functions. A significant number of protease inhibitors have also been shown to possess antimicrobial activity, presumed to contribute in defense against pathogenic microorganisms as plants with higher levels of protease inhibitors tend to exhibit increased resistance towards pathogens. Two proposed mechanisms for the antimicrobial activity are combating microbial proteases that play roles in disease development and disruption of microbial cell wall & membrane necessary for survival. Here we show for the first time a novel activity of soybean trypsin inhibitor and bovine aprotinin that they nick supercoiled, circular plasmid DNA. A number of experiments conducted to demonstrate the observed DNA nicking activity is inherent, rather than a co-purified, contaminating nuclease. The nicking of the plasmid results in markedly reduced efficiencies in transformation of E. coli and transfection of HEK293T cells. Thus, this work reveals yet a new mechanism for the antimicrobial activity by protease inhibitors.

The antiviral activity of naturally occurring proteins and their peptide fragments after chemical modification

Chemical modification of the proteins bovine serum albumin, alpha-lactalbumin, beta-lactoglobulin and chicken lysozyme by 3-hydroxyphthalic anhydride (3-HP) yielded compounds which exerted antiviral activity in vitro as compared with the native unmodified proteins. Of the three enveloped viruses tested, human herpes simplex virus type 1 (HSV-1), bovine parainfluenza virus type 3 and porcine respiratory corona virus, only HSV-1 proved sensitive to the 3-HP-proteins. All of the chemically modified proteins presented antiviral activity against HSV-1 when assayed before, during or after infection. However, to achieve HSV-1 inhibition, significantly higher concentrations of the modified proteins were required if present before infection as compared to during or after infection. Our results suggest that multiple mechanisms are involved in the inhibition of HSV-1 infection. Proteolytical digestion of albumin, alpha-lactalbumin, beta-lactoglobulin and lysozyme by trypsin, chymotrypsin and pepsin yielded several peptide fragments with antiherpetic activity. Chemical modification of these peptide fragments by 3-HP generated peptides with antiviral activity, however, this was almost always combined with a cytotoxic effect on the Vero cells. Overall, our results suggest that targeted chemical modification of some natural products might provide compounds effective against HSV-1 infection.

Effect of antimicrobial apomyoglobin 56-131 peptide on liposomes and planar lipid bilayer membrane

The horse apomyoglobin 56-131 peptide is a convenient object for studies on the recently discovered antimicrobial activities of haem-binding protein fragments called haemocidins. The purpose of this study was to determine the effect of this peptide on planar lipid bilayer membranes and on liposomes of different lipid compositions. Micromolar concentrations of the apomyoglobin 56-131 fragment disrupt phosphatidylserine/phosphatidylethanolamine planar lipid bilayers without discrete conductance changes. The observed detergent-like action is dependent on peptide concentration; the lower amount of peptide resulted in longer bilayer lifetime. The cholesterol has an inhibitory effect on peptide-induced liposome lysis as shown by calcein release from liposomes. Additionally, there was considerable lytic activity on liposomes formed from anionic lipids of the sort found in bacterial membranes. Circular dichroism (CD) experiments showed that the peptide had a disordered structure in aqueous solutions and folds gradually to form helices in both membrane-mimetic trifluoroethanol solutions as well as in liposome suspensions. The features of the apomyoglobin 56-131 fragment that are similar to the cationic antimicrobial peptides acting in a 'carpet-like' manner are discussed.

A protease inhibitor of the Kunitz family from skin secretions of the tomato frog, Dyscophus guineti (Microhylidae)

Norepinephrine-stimulated skin secretions of the tomato frog, Dyscophus guineti, contained a trypsin inhibitor whose primary structure was established as: SPAEVCF LPK(10) ESGLCRARAL(20) RYYYDRGDGK(30) CEEFIYGGCG(40) GNGNNY KSLL(50) TCKISCE. This amino acid sequence identifies the peptide as a member of the Kunitz/bovine pancreatic trypsin inhibitor (BPTI) family and demonstrates that selective evolutionary pressure has acted to conserve those domains in the molecule (corresponding to positions 12-18 and 34-39 in BPTI) that interact with trypsin. Extracellular proteases produced by pathogenic microorganisms play important roles in facilitating invasion of the host and broad spectrum antimicrobial activity of BPTI has been described. Cationic, amphipathic alpha-helical antimicrobial peptides of the magainin type, important in the defense strategy of several species of frog, were not detected in the skin secretions. We speculate, therefore, that synthesis of a proteinase inhibitor in the skin of the tomato frog may be a component of an alternative strategy of this animal to defend itself against microorganisms.

Design of synthetic bactericidal peptides derived from the bactericidal domain P(18-39) of aprotinin

A bactericidal domain, P(18-39), of the proteinase inhibitor aprotinin, possesses the structural feature of two antiparallel beta-sheets connected by a short turn. In order to understand the structural requirements for antibacterial activity, two peptides, each having the sequence corresponding to a single beta-sheet structure of P(18-39), were synthesized and their antibacterial properties investigated. One peptide, P(18-28), with the sequence IIRYFYNAKAG, was active against almost all the bacterial strains investigated. However, the bactericidal activity of P(18-28) was reduced compared to the parent molecule, P(18-39). The other peptide, P(29-39), with the sequence LCQTFVYGGCR, was only weakly bactericidal against Pseudomonas aeruginosa. A peptide, P(18-26), devoid of the C-terminus dipeptide Ala-Gly of P(18-28), retained the bactericidal activity of P(18-28) against most of the bacterial strains investigated. Only Klebsiella pneumoniae, P. aeruginosa and Staphylococcus aureus were resistant to P(18-26). Replacement of lysine 26 by arginine in P(18-26) (IIRYFYNAR) improved the bactericidal activity. The retropeptide, RANYFYRII, retained the antibacterial activity of IIRYFYNAR toward Gram-negative bacteria, but it was less active against Gram-positive bacteria. The random peptide, IANRIYRYF, was as bactericidal as IIRYFYNAR. Moreover, the random peptide possessed, in contrast to IIRYFYNAR, a strong antifungal activity against Candida albicans. Elimination of the N-hydrophobic terminal Ile-Ile from P(18-26) (RYFYNAK) strongly reduced the bactericidal potency of the peptide. Attaching the hydrophobic peptide, FFVAP, to the C-terminal of P(18-26) (IIRYFYNAKFFVAP) increased the bactericidal potency of the peptides considerably. We concluded that the order of the amino acids in the sequence of the peptides is not, per se, a critical feature for bactericidal activity. Hydrophobic interaction between peptide and bacterial membrane is probably the most important feature involved in the bactericidal mechanism of the antibiotic peptides.

Different modes of inhibition of human adenovirus proteinase, probably a cysteine proteinase, by bovine pancreatic trypsin inhibitor

The type of proteinase and the nature of the active site of the human adenovirus proteinase are unknown. For these reasons we produced an inhibitor profile of the enzyme. Enzyme activity in disrupted virions was inhibited by several serine-specific as well as cysteine-specific proteinase inhibitors. Of the inhibitors that worked, the most useful potentially in illuminating the nature of the active site was bovine pancreatic trypsin inhibitor (BPTI), and for this reason we extensively characterized the interaction with BPTI. In disrupted virions, the enzyme is irreversibly inhibited by BPTI with a Ki of 35 nM and a ki of 6.2 x 10(-4) s(-1). One reason enzyme activity is inhibited is that BPTI, a basic protein, precipitates the viral DNA, a cofactor of enzyme activity. In vitro with purified components, BPTI acts as a competitive inhibitor (Ki 2 microM) of the recombinant proteinase complexed with its 11-amino-acid cofactor pVIc. The recombinant endoproteinase is beat labile whereas its 11-amino-acid cofactor is heat stable. We estimate there are about 50 molecules of proteinase per virus particle.