Peptide derived from the lipid binding domain of Group IB human pancreatic phospholipase A2 possesses antibacterial activity

Group 1B human pancreatic secretory phospholipase A₂ (hp-sPLA₂), a digestive enzyme synthesized by pancreatic acinar cells and present in pancreatic juice, do not have antibacterial activity towards Escherichia coli. Our earlier results suggest that the N-terminal first ten amino acid residues of hp-sPLA₂ constitute major portion of the membrane binding domain of full-length enzyme and is responsible for the precise orientation of enzyme on the membrane surface by inserting into the lipid bilayers (Pande et al. (2006) Biochemistry, 45,12436–12447). In this study we report the antibacterial properties of a peptide (AVWQFRKMIK-CONH₂; N10 peptide), which corresponds to the N-terminal first ten amino acid residues of hp-sPLA₂, against E. coli. Full-length hp-sPLA₂, which contains this peptide sequence as N-terminal α-helix, did not showed detectable antibacterial activity. Presence of physiological concentration of salt or preincubation of N10 peptide with soluble anionic polymer inhibits the antibacterial activity indicating the importance of electrostatic interaction in binding of peptide to bacterial membrane. Addition of peptide resulted in destabilization of outer as well as inner cytoplasmic membrane of E. coli suggesting bacterial membranes to be the main target of action. N10 peptide exhibits strong synergism with lysozyme and potentiates the antibacterial activity of lysozyme. The peptide was inactive against human erythrocyte. Our result shows for the first time that a peptide fragment of hp-sPLA₂ possesses antibacterial activity towards E. coli and at subinhibitory concentration and can potentiate the antibacterial activity of membrane active enzyme. These observations suggest that N10 peptide may play an important role in the antimicrobial activity of pancreatic juice.     

The use of real-time PCR and species-specific primers for the identification and monitoring of Paecilomyces lilacinus

The Paecilomyces lilacinus is the most widely tested fungus for the control of root-knot and cyst nematodes. The fungus has also been implicated in a number of human and animal infections, difficulties in diagnosis often result in misdiagnosis or delays in identification leading to a delay in treatment. Here, we report the development of species-specific primers for the identification of P. lilacinus based on sequence information from the ITS gene, and their use in identifying P. lilacinus isolates, including clinical isolates of the fungus. The primer set generated a single PCR fragment of 130 bp in length that was specific to P. lilacinus and was also used to detect the presence of P. lilacinus from soil, roots and nematode eggs. Real-time PCR primers and a TaqMan probe were also developed and provided quantitative data on the population size of the fungus in two field sites. PCR, bait and culture methods were combined to investigate the presence and abundance of the fungus from two field sites in the United Kingdom where potato cyst nematode populations were naturally declining, and results demonstrated the importance of using a combination of methods to investigate population size and activity of fungi.     

Phylloplane bacteria increase seedling emergence, growth and yield of field-grown groundnut (Arachis hypogaea L.)

AIM: To isolate and characterize groundnut-associated bacterial isolates for growth promotion of groundnut in field. METHODS AND RESULTS: Three hundred and ninety-three groundnut-associated bacteria, representing the geocarposphere, phylloplane and rhizosphere, and endophytes were applied as seed treatment in greenhouse. Maximum increase in plant biomass (up to 26%) was observed following treatment with a rhizosphere isolate identified as Bacillus firmis GRS 123, and two phylloplane isolates Bacillus megaterium GPS 55 and Pseudomonas aeruginosa GPS 21. There was no correlation between the production of L-tryptophan-derived auxins and growth promotion by the test isolates. Actively growing cells and peat formulations of GRS 123 and GPS 55, and actively growing cells of GPS 21, significantly increased the plant growth and pod yield (up to 19%) in field. Rifampicin-resistant mutants of GRS 123 and GPS 21 colonized the ecto- and endorhizospheres of groundnut, respectively, up to 100 days after sowing (DAS), whereas GPS 55 was recovered from both the habitats at 100 DAS. CONCLUSION: Seed bacterization with phylloplane isolates promoted groundnut growth indicating the possibility of isolating rhizosphere beneficial bacteria from different habitats. SIGNIFICANCE AND IMPACT OF THE STUDY: Identification of phylloplane bacteria as effective plant growth-promoting rhizobacteria (PGPR) broadens the spectrum of PGPR available for field application.     

Dimerization of the p53 oligomerization domain: identification of a folding nucleus by molecular dynamics simulations

Dimerization of the p53 oligomerization domain involves coupled folding and binding of monomers. To examine the dimerization, we have performed molecular dynamics (MD) simulations of dimer folding from the rate-limiting transition state ensemble (TSE). Among 799 putative transition state structures that were selected from a large ensemble of high-temperature unfolding trajectories, 129 were identified as members of the TSE via calculation of a 50% transmission coefficient from at least 20 room-temperature simulations. This study is the first to examine the refolding of a protein dimer using MD simulations in explicit water, revealing a folding nucleus for dimerization. Our atomistic simulations are consistent with experiment and offer insight that was previously unobtainable.     

Role of third extracellular domain of plasma membrane Ca2+-Mg2+-ATPase based on the novel inhibitor caloxin 3A1

The plasma membrane Ca2+ pump (PMCA) is a Ca2+-Mg2+-ATPase that expels Ca2+ from cells to help them maintain low concentrations of cytosolic Ca2+ ([Ca2+]i). It contains five putative extracellular domains (PEDs). Earlier we had reported that binding to PED2 leads to PMCA inhibition. Mutagenesis of residues in transmembrane domain 6 leads to loss of PMCA activity. PED3 connects transmembrane domains 5 and 6. PED3 is only five amino acid residues long. By screening a phage display library, we obtained a peptide sequence that binds this target. After examining a number of peptides related to this original sequence, we selected one that inhibits the PMCA pump (caloxin 3A1). Caloxin 3A1 inhibits PMCA but not the sarcoplasmic reticulum Ca2+-pump. Caloxin 3A1 did not inhibit formation of the 140 kDa acylphosphate intermediate from ATP or its degradation. Thus, PEDs play a role in the reaction cycle of PMCA even though sites for binding to the substrates Ca2+ and Mg-ATP2-, and the activator calmodulin are all in the cytosolic domains of PMCA. In endothelial cells exposed to low concentration of a Ca2+-ionophore, caloxin 3A1 caused a further increase in [Ca2+]i proving its ability to inhibit PMCA pump extracellularly. Thus, even though PED3 is the shortest PED, it plays key role in the PMCA function.     

Molecular recognition of 15-deoxy-delta(12,14)-prostaglandin J2 by nuclear factor-kappa B and other cellular proteins

15-Deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2), a dehydration product of prostaglandin D2, is an important pharmacological molecule, which with the virtue of its electrophilicity, has been reported to covalently modify some cellular proteins (such as nuclear factor-kappa B (NF-kappaB), AP-1, p53, and thioredoxin) and elicit its physiological effects. The aim of the present computational study is to understand the role molecular recognition plays in the association of 15d-PGJ2 with NF-kappaB and other proteins. Another aim is to characterize whether p53 is a direct target for covalent modification by 15d-PGJ2. A docking strategy is applied along with calculation of ab initio electrostatic potential maps to analyze the mode of binding of prostaglandin molecule with critical cysteine-containing sites in each protein. The results provide identification of important sites in the target proteins, which provide recognition and stability to the prostaglandin molecule. Fit of shape and complementarity of electrostatic interactions are derived as significant determinants of molecular recognition of 15d-PGJ2. Further, comparative results indicate that p53 protein may also be a target for direct modification by 15d-PGJ2. The molecular models obtained should allow the rational design of more specific analogs of 15d-PGJ2.     

Plasma membrane calcium pumps in smooth muscle: from fictional molecules to novel inhibitors

Plasma membrane Ca2+ pumps (PMCA pumps) are Ca2+-Mg2+ ATPases that expel Ca2+ from the cytosol to extracellular space and are pivotal to cell survival and function. PMCA pumps are encoded by the genes PMCA1, -2, -3, and -4. Alternative splicing results in a large number of isoforms that differ in their kinetics and activation by calmodulin and protein kinases A and C. Expression by 4 genes and a multifactorial regulation provide redundancy to allow for animal survival despite genetic defects. Heterozygous mice with ablation of any of the PMCA genes survive and only the homozygous mice with PMCA1 ablation are embryolethal. Some PMCA isoforms may also be involved in other cell functions. Biochemical and biophysical studies of PMCA pumps have been limited by their low levels of expression. Delineation of the exact physiological roles of PMCA pumps has been difficult since most cells also express sarco/endoplasmic reticulum Ca2+ pumps and a Na+-Ca2+-exchanger, both of which can lower cytosolic Ca2+. A major limitation in the field has been the lack of specific inhibitors of PMCA pumps. More recently, a class of inhibitors named caloxins have emerged, and these may aid in delineating the roles of PMCA pumps.     

Oligomerization and phase transitions in aqueous solutions of native and truncated human beta B1-crystallin

Human betaB1-crystallin is a major eye-lens protein that undergoes in vivo truncation at the N-terminus with aging. By studying native betaB1 and truncated betaB1DeltaN41, which mimics an age-related in vivo truncation, we have determined quantitatively the effect of truncation on the oligomerization and phase transition properties of betaB1 aqueous solutions. The oligomerization studies show that the energy of attraction between the betaB1DeltaN41 proteins is about 10% greater than that of the betaB1 proteins. We have found that betaB1DeltaN41 aqueous solutions undergo two distinct types of phase transitions. The first phase transition involves an initial formation of thin rodlike assemblies, which then evolve to form crystals. The induction time for the formation of rodlike assemblies is sensitive to oligomerization. The second phase transition can be described as liquid-liquid phase separation (LLPS) accompanied by gelation within the protein-rich phase. We refer to this process as heterogeneous gelation. These two phase transitions are not observed in the case of betaB1 aqueous solutions. However, upon the addition of poly(ethylene glycol) (PEG), we observe heterogeneous gelation also for betaB1. Our PEG experiments allow us to estimate the difference in phase separation temperatures between betaB1 and betaB1DeltaN41. This difference is consistent with the increase in energy of attraction found in our oligomerization studies. Our work suggests that truncation is a cataractogenic modification since it favors protein condensation and the consequent formation of light scattering elements, and highlights the importance of the N-terminus of betaB1 in maintaining lens transparency.     

Modulation of human 5-lipoxygenase activity by membrane lipids

Mammalian 5-lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid (AA) to leukotrienes, potent inflammatory mediators. 5-LO is activated by a Ca(2+)-mediated translocation to membranes, and demonstrates the characteristic features of interfacially activated enzymes, yet the mechanism of membrane binding of 5-LO is not well understood. In an attempt to understand the mechanism of lipid-mediated activation of 5-LO, we have studied the effects of a large set of lipids on human recombinant 5-LO activity, as well as mutual structural effects of 5-LO and membranes. In the presence of 0.35 mM phosphatidylcholine (PC) and 0.2 mM Ca(2+), there was substrate inhibition at >100 microM AA. Data analysis at low AA concentrations yielded the following: K(m) approximately 103 microM and k(cat) approximately 56 s(-1). 5-LO activity was supported by PC more than by any other lipid tested except for a cationic lipid, which was more stimulatory than PC. Binding of 5-LO to zwitterionic and acidic membranes was relatively weak; the extent of binding increased 4-8 times in the presence of Ca(2+), whereas binding to cationic membranes was stronger and essentially Ca(2+)-independent. Polarized attenuated total reflection infrared experiments implied that 5-LO binds to membranes at a defined orientation with the symmetry axis of the putative N-terminal beta-barrel tilted approximately 45 degrees from the membrane normal. Furthermore, membrane binding of 5-LO resulted in dehydration of the membrane surface and was paralleled with stabilization of the structures of both 5-LO and the membrane. Our results provide insight into the understanding of the effects of membrane surface properties on 5-LO-membrane interactions and the interfacial activation of 5-LO.