Francesc Rabanal - Academia.edu (original) (raw)

Papers by Francesc Rabanal

Encyclopedia of Reagents for Organic Synthesis, Oct 15, 2004

International journal of peptide & protein research, Jan 12, 2009

The synthesis of three hepatitis B surface antigens derived from S and pre-S proteins (adw S(140-... more The synthesis of three hepatitis B surface antigens derived from S and pre-S proteins (adw S(140-147), [Tyr148] adw S(139-148), and adw pre-S(120-145)) has been accomplished by the continuous flow Fmoc-polyamide solid phase method. The use of different scavengers and trimethylsilyl bromide (TMSBr) in trifluoroacetic acid as deprotecting procedures is discussed.

PubMed, Oct 1, 1996

Although volatile general anesthetics interact with several proteins, little is known about the l... more Although volatile general anesthetics interact with several proteins, little is known about the location or characteristics of the binding sites at the molecular level. A detailed structural description of how anesthetics associate with macromolecules is necessary for understanding anesthetic mechanisms of action. The recent introduction of designed synthetic proteins provides new opportunities for obtaining structural and functional information on anesthetic-protein interactions. A synthetic tetra-alpha-helix-bundle protein was used to examine the interaction of halothane with a designed protein interior. The tetra-alpha-helix-bundle comprises 124 residues in the form of two identical 62-residue di-alpha-helical peptides, held together in an all-parallel bundle by hydrophobic forces. Steady-state and time-resolved tryptophan fluorescence and circular dichroism spectroscopy were used to study the anesthetic-protein interaction. Halothane quenches bundle tryptophan fluorescence with a dissociation constant of 2.3 +/- 0.4 mM and a Hill number of 0.9 +/- 0.1. Tryptophan fluorescence decay analysis indicates that halothane quenches the protein fluorescence by a static mechanism. Circular dichroism spectroscopy revealed no change in protein secondary structure on exposure to halothane. Dissociation of the tetra-alpha-helix-bundle into 62-residue di-alpha-helical peptides by trifluoroethanol eliminated the halothane-protein interaction. The results suggest that halothane binds to the hydrophobic interior of the tetra-alpha-helix-bundle, close to the tryptophan residues. The protein tertiary and quaternary structures are required for anesthetic binding. This study demonstrates the feasibility of using synthetic tetra-alpha-helix-bundles as model anesthetic-binding proteins. The use of de novo designed bundle proteins should allow structural, energetic and functional descriptions of anesthetic-protein interactions.

Journal of Mass Spectrometry, Dec 13, 2018

In this work the extraction, structural analysis and identification as well as antimicrobial, ant... more In this work the extraction, structural analysis and identification as well as antimicrobial, anti-adhesive and anti-biofilm activities of lipopeptides produced by Enterobacter cloacae C3 strain were studied. A combination of chromatographic and spectroscopic techniques offers opportunities for a better characterization of the biosurfactant structure. Thin layer chromatography (TLC) and HPLC for amino acid composition determination are used. Efficient spectroscopic techniques have been utilized for investigations on the biochemical structure of biosurfactants, such as Fourier transform infrared (FT-IR) spectroscopy and mass spectrometry analysis. This is the first work describing the production of different isoforms belonging to kurstakin and surfactin families by E. cloacae strain. Three kurstakin homologues differing by the fatty acid chain length from C 10 to C 12 were detected. The spectrum of lipopeptides belonging to surfactin family contains various isoforms differing by the fatty acid chain length as well as the amino acids at positions four and seven. Lipopeptide C3 extract exhibited important antibacterial activity against Gram-positive and Gramnegative bacteria, antifungal activity and interesting anti-adhesive and disruptive properties against biofilm formation by human pathogenic bacterial strains: Salmonella typhimurium, Klebsiella pneumoniae, Staphylococcus aureus, Bacillus cereus and Candida albicans.

Proceedings of the National Academy of Sciences of the United States of America, Sep 1, 1998

We report the construction of a synthetic f lavo-heme protein that incorporates two major physiol... more We report the construction of a synthetic f lavo-heme protein that incorporates two major physiological activities of f lavoproteins: light activation of f lavin analogous to DNA photolyase and rapid intramolecular electron transfer between the f lavin and heme cofactors as in several oxidoreductases. The functional tetra-␣-helix protein comprises two 62-aa helix-loop-helix subunits. Each subunit contains a single cysteine to which f lavin (7-acetyl-10-methylisoalloxazine) is covalently attached and two histidines appropriately positioned for bis-his coordination of heme cofactors. Both f lavins and hemes are situated within the hydrophobic core of the protein. Intramolecular electron transfer from f lavosemiquinone generated by photoreduction from a sacrificial electron donor in solution was examined between protoporphyrin IX and 1-methyl-2-oxomesoheme XIII. Laser pulseactivated electron transfer from f lavin to meso heme occurs on a 100-ns time scale, with a favorable free energy of approximately ؊100 meV. Electron transfer from f lavin to the lower potential protoporphyrin IX, with an unfavorable free energy, can be induced after a lag phase under continuous light illumination. Thus, the supporting peptide matrix provides an excellent framework for the positioning of closely juxtaposed redox groups capable of facilitating intramolecular electron transfer and begins to clarify in a simplified and malleable system the natural engineering of f lavoproteins.

Ecotoxicology and Environmental Safety, 2019

This work aimed to study the potential of a newly marine bacterium, Bacillus stratosphericus FLU5... more This work aimed to study the potential of a newly marine bacterium, Bacillus stratosphericus FLU5, to produce an efficient surface active agent BS-FLU5. Biosurfactant production was examined on different carbon sources using the surface tension measurement and the oil displacement test. Strain FLU5 showed its capacity to produce biosurfactants on the most of tested substrates and in particular the residual frying oil, which is an alternative, cheap and renewable carbon source, thus minimizing the high cost of producing surfactants. MALDI-TOF MS/MS analyses confirmed the presence of lipopeptides identified as members of surfactin and pumilacidin isomers. The critical micellar concentration of the purified lipopeptides produced by strain FLU5 was 50 mg/l and, at this concentration, the surface tension of the water was reduced from 72 to 28 mN/m. Furthermore, the crude lipopeptides showed interest stability against a broad range of pH (2.1-12), temperature (10-121 °C) and salinity (0-120 g/l NaCl). The biosurfactant BS-FLU5 demonstrated negligible cytotoxic effect against mammalian cells (HEK293 human embryonic kidney cell line) at all of tested concentration (125-1000 µg/ml). The application of BS-FLU5 in oil recovery from soil contaminated by hydrocarbons (used motor oil) showed that it was more effective on the hydrocarbon-remobilization than some tested synthetic surfactants. These results highlight the applicability of the lipopeptides produced by the new marine Bacillus stratosphericus strain FLU5 in different fields, especially in environmental remediation processes. Production of lipopeptides is a characteristic of several Bacillus species, but to the best of our knowledge, this is the first report showing the potential of Bacillus stratosphericus for efficient production of biosurfactants or lipopeptides.

Journal of Polymers and the Environment

Springer eBooks, 2016

The emergence of pathogens which are resistant or multi-drug resistant to most of the currently a... more The emergence of pathogens which are resistant or multi-drug resistant to most of the currently available antibiotics is posing an immense burden to the healthcare systems throughout the world. The development of new classes of antibiotics has also suffered a decline since many pharmaceutical companies have gradually abandoned the field. Fortunately, several public–private initiatives to spur the development of new antibiotics have been recently launched. Antimicrobial peptides are thus attracting a renewed interest as potential therapeutic antibiotic candidates. In fact, some of the oldest available antibiotics in the market are cyclic antimicrobial peptides, such as polymyxin B, colistin, gramicidin or bacitracin. However, pharmacological and toxicological problems associated with the systemic use of antimicrobial peptides are slowing their development and drug approval. An overview of the advantages and drawbacks of antimicrobial peptides as antibiotic drugs and a report of compounds that are in development are described.

Process Biochemistry, Sep 1, 2022

Pharmaceutics, Apr 21, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Luminescence, 2005

We have designed synthetic peptides that mimic the primary and secondary structure of the cationi... more We have designed synthetic peptides that mimic the primary and secondary structure of the cationic lipopeptide antibiotic polymyxin B (PxB) in order to determine the structural requirements for membrane action and to assess possible therapeutic potential. Two analogues with related sequences to that of PxB, but including synthetic simplifications (disulphide bridge between two cysteines in positions 4 and 10, N‐terminal nonanoic acid), have been synthesized. Peptide–lipid interactions have been studied by fluorescence resonance energy transfer between pyrene and 4,4‐difluoro‐5‐methyl‐4‐bora‐3α,4α‐diaza‐s‐indacene‐3‐dodecanoyl (BODIPY®) probes covalently linked to phospholipids, and the possibility of membrane disruption or permeabilization has been assessed by light scattering and fluorescence quenching assays. The synthetic peptide sP‐B, which closely mimics the primary and secondary structures of PxB, binds to vesicles of anionic 1‐palmitoyl‐2‐oleoylglycero‐sn‐3‐phosphoglycerol (POPG) or of lipids extracted from Escherichia coli membranes, and induces apposition of the vesicles and selective lipid exchange without permeabilization of the membrane. We conclude that sP‐B forms functional vesicle–vesicle contacts that are selective, as previously described for PxB. The second analogue, sP‐C, has a permutation of two amino acids that breaks the hydrophobic patch formed by d‐Phe and Leu residues on the cyclic part of the sequence. sP‐C lipopeptide is more effective than sP‐B in inducing lipid mixing, but shows no selectivity for the lipids that exchange through the vesicle–vesicle contacts, and at high concentrations has a membrane‐permeabilizing effect. The deacylated and non‐antibiotic derivative PxB‐nonapeptide (PxB‐NP) does not induce the formation of functional intervesicle contacts in the range of concentrations studied. Copyright © 2005 John Wiley & Sons, Ltd.

Journal of Nanobiotechnology, Oct 31, 2020

Infectious diseases kill over 17 million people a year, among which bacterial infections stand ou... more Infectious diseases kill over 17 million people a year, among which bacterial infections stand out. From all the bacterial infections, tuberculosis, diarrhoea, meningitis, pneumonia, sexual transmission diseases and nosocomial infections are the most severe bacterial infections, which affect millions of people worldwide. Moreover, the indiscriminate use of antibiotic drugs in the last decades has triggered an increasing multiple resistance towards these drugs, which represent a serious global socioeconomic and public health risk. It is estimated that 33,000 and 35,000 people die yearly in Europe and the United States, respectively, as a direct result of antimicrobial resistance. For all these reasons, there is an emerging need to find novel alternatives to overcome these issues and reduced the morbidity and mortality associated to bacterial infectious diseases. In that sense, nanotechnological approaches, especially smart polymeric nanoparticles, has wrought a revolution in this field, providing an innovative therapeutic alternative able to improve the limitations encountered in available treatments and capable to be effective by theirselves. In this review, we examine the current status of most dangerous human infections, together with an in-depth discussion of the role of nanomedicine to overcome the current disadvantages, and specifically the most recent and innovative studies involving polymeric nanoparticles against most common bacterial infections of the human body.

Annals of Microbiology, Apr 10, 2015

Biopolymers, Dec 6, 1998

The interaction of the immunogenic peptide of human hepatitis B virus (HBV) preS(120-145), includ... more The interaction of the immunogenic peptide of human hepatitis B virus (HBV) preS(120-145), including B and T epitopes, with phospholipid vesicles has been studied by fluorescence techniques and CD. In addition, interaction of three lipopeptides derived from preS(120-145) containing stearoyl, cholanoyl, and tripalmitoyl-S-glyceryl-cysteine (Pam3C) SS moieties with dipalmitoylphosphatidylcholine (DPPC) has been investigated by polarization fluorescence spectroscopy. Fluorescence experiments showed an increase in fluorescence intensity and a blue shift of the maximum emission wavelength upon interaction of preS(120-145) with DPPC vesicles below the transition temperature (Tc), indicating that the tryptophan moiety enters a more hydrophobic environment. Moreover, fluorescence polarization experiments showed that the peptide decreased the membrane fluidity at the hydrophobic core, increasing the Tc of the lipid and decreasing the amplitude of the change of fluorescence polarization associated with the cooperative melting of 1,6-diphenyl-1,3,5-hexatriene labeled vesicles. The absence of leakage of vesicle-entrapped carboxyfluorescein indicates that the peptide did not promote vesicle lysis. Besides, the three lipopeptides derived from preS(120-145) showed a more pronounced rigidifying effect at the hydrophobic core of the bilayer, with a significative increase in the Tc. Stearoyl- and cholanoyl-preS(120-145) restricted the motion of lipids also at the polar surface, whereas Pam3CSS-preS(120-145) did not alter the polar head group order. Finally, CD studies in 2,2,2-trifluoroethanol or in presence of vesicles suggested that the bound peptide adopted amphiphilic alpha-helical and beta-sheet structures, with an important contribution of the beta-turn. It is concluded that preS(120-145) can interact with the lipid membrane through the formation of an amphipathic structure combination of beta-sheet and alpha-helix aligned parallel to the membrane surface, involving the N-terminal residues, and penetrating only a short distance into the hydrophobic core. The C-terminal part, with a combination of beta-turn and beta-sheet structure, remains at the outer part of the bilayer, being potentially accessible to immunocompetent cells. Furthermore, coupling of an hydrophobic moiety to the N-terminal part of the peptide favors anchoring to the membrane, probably facilitating interaction of the peptide with the immunoglobulin receptor. These results are in agreement with the induction of immune response by preS(120-145) and with the enhanced immunogenicity found in general for lipid-conjugated immunopeptides.

Journal of Physical Chemistry B, Feb 7, 2006

Scientific Reports, Mar 25, 2015

Hydrophobic mismatch is a well-recognized principle in the interaction of transmembrane proteins ... more Hydrophobic mismatch is a well-recognized principle in the interaction of transmembrane proteins with lipid bilayers. This concept was extended here to amphipathic membranolytic a-helices. Nine peptides with lengths between 14 and 28 amino acids were designed from repeated KIAGKIA motifs, and their helical nature was confirmed by circular dichroism spectroscopy. Biological assays for antimicrobial activity and hemolysis, as well as fluorescence vesicle leakage and solid-state NMR spectroscopy, were used to correlate peptide length with membranolytic activity. These data show that the formation of transmembrane pores is only possible under the condition of hydrophobic matching: the peptides have to be long enough to span the hydrophobic bilayer core to be able to induce vesicle leakage, kill bacteria, and cause hemolysis. By correlating the threshold lengths for biological activity with the biophysical results on model vesicles, the peptides could be utilized as molecular rulers to measure the membrane thickness in different cells. M embrane-active antimicrobial peptides (AMPs) are found in almost all types of organisms and constitute a host defense system against microorganisms 1. Over 2000 AMPs are known 2 and can be classified according to origin, activity or structure 1-3. Linear cationic amphipathic a-helices are the most common AMPs and also have the widest antimicrobial activity spectrum, some well-known examples being magainins from frogs 4 and LL-37 from humans 5. Besides exploring natural AMPs from a wide variety of organisms, much effort has also been spent to obtain new peptides with improved activities. One approach is to modify natural sequences, while another strategy is based on the design of amphipathic sequences from scratch, as in the case of MSI-103 with the regular repeat (KIAGKIA) 3-NH 2 3. This heptameric motif was based on the sequence of PGLa, a member of the magainin family of antimicrobial peptides from the African frog Xenopus laevis 6. The full-length peptide was optimized by simplifying the sequence to contain only four types of amino acid, and by increasing the positive charge while maintaining the overall amphipathic character 3. MSI-103 was found to have a higher antimicrobial activity than the parent peptide, while hemolytic side effects were reduced 3,7. The parent peptide of MSI-103, PGLa, as well as magainin 2 from the same family, have been proposed to permeabilize membranes by forming pores across the lipid bilayer 8-10. Pores are attributed to peptides in a transmembrane orientation, forming either a so-called ''barrel-stave'' as described for alamethicin 11 , or a ''toroidal wormhole'' that includes lipid head groups as reported, e.g., for melittin 12. For melittin, there is strong indication of membranous pores from X-ray studies, but the orientation of the peptide is not visible from these experiments 12. Complementary methods, such as solid-state NMR and oriented circular dichroism, have been used to monitor directly the alignment of helical peptides and thereby discriminate a surface-bound state from a stable transmembrane alignment and from any tilted state in between 13-19. This way, MSI-103 was shown to selfassemble and start to insert into lipid bilayers in a similar manner to its parent peptide PGLa, but at a lower threshold concentration 7,15,20-24. The same kind of solid-state NMR studies have also been instrumental in deciphering the phenomenon of hydrophobic matching, which is known to affect the tilt angle and assembly of fully inserted transmembrane protein segments 25-29. It is generally recognized that long membrane-spanning helices can become tilted to match