Molecular Identification and Antifungal Susceptibility of Clinical Isolates of Sporothrix schenckii Complex in Medellin,Colombia

Background

Sporotrichosis is a subcutaneous mycosis that affects humans and other animals. Infection prevails in tropical and subtropical countries. Until a few years ago, it was considered that two varieties of Sporothrix schenckii caused this mycosis, but by applying molecular taxonomic markers, it has been demonstrated that there are several cryptic species within S. schenckii complex which varies in susceptibility, virulence, and geographic distribution.

Objective

This study aimed to identify the clinical isolates of Sporothrix spp. from patients with sporotrichosis in Medellin, Colombia, using two markers and to evaluate the in vitro susceptibility to itraconazole.

Methods

Thirty-four clinical isolates of Sporothrix spp. from Colombia, three from Mexico, and one from Guatemala were identified through sequencing of the noncoding region ITS-1?+?5.8SDNAr?+?ITS-2 and of the fragment containing exons 3 and 4 of the β-tubulin gene. Clinical isolate sequences were compared with GenBank reference sequences using the BLASTN tool, and then, phylogenetic analysis was performed. Besides, the in vitro susceptibility to itraconazole was evaluated by determining the minimum inhibitory concentrations according to the CLSI M38-A2 method.

Results

Clinical isolates were identified by morphology as Sporothrix spp. Using the molecular markers, ITS and β-tubulin, isolates were identified as S. schenckii sensu stricto (25) and Sporothrix globosa (13). Susceptibility to itraconazole was variable among clinical isolates.

Conclusion

This is the first scientific publication that identifies species that cause sporotrichosis in Colombia, along with the antifungal susceptibility to itraconazole.

     

Trivaline Molecular Complexes with Trinucleotides Form in Solution the Extended,about 1000 Å in Length Structures

Abstract

The fluorescence, flow linear dichroism and electron microscopy (EM) have shown the trivaline ability to interact in solution with certain molecules of trinucleotides. This interaction results in formation of extended structures up to several. thousand angstroms in length. Such structures were observed for trivaline complexes with homopurine, homopyrimidine or random sequences of deoxyribo- and ribonucleotides, independently of the presence or absence of the terminal 5′-phosphate residue. A model of such a structural organization is proposed. An elementary structural unit consists of a trivaline β-dimer and adsorbed trinucleotide. So, “dimeric” complex is formed. Two such “dimeric” complexes combine with each other by means of peptide-peptide contacts (as with β-sandwich). So, “tetrameric” complex is formed It has a dyad axis. Two such structural units combine with each other by means of Hoogsteen's hydrogen bonds. So, “octamreic” complex is formed. It has three mutually perpendicular dyad axes. The “octameric” complexes appear to be able to combine with each other by means of stacking interactions, and to form the regular organized aggregates consisting of many dozens of elementary units. So, “stacking” structure is formed. The “octameric” complex is the symmetry translational unit of such a stucture. The spatial position of the bases in all these structures is additionally fixed by the nucleo-peptide interactions. These aggregates have the appearance of extended structures on electron micrographs.     

Self-assembling systems comprising intrinsically disordered protein polymers like elastin-like recombinamers

Despite lacking cooperatively folded structures under native conditions, numerous intrinsically disordered proteins (IDPs) nevertheless have great functional importance. These IDPs are hybrids containing both ordered and intrinsically disordered protein regions (IDPRs), the structure of which is highly flexible in this unfolded state. The conformational flexibility of these disordered systems favors transitions between disordered and ordered states triggered by intrinsic and extrinsic factors, folding into different dynamic molecular assemblies to enable proper protein functions. Indeed, prokaryotic enzymes present less disorder than eukaryotic enzymes, thus showing that this disorder is related to functional and structural complexity. Protein-based polymers that mimic these IDPs include the so-called elastin-like polypeptides (ELPs), which are inspired by the composition of natural elastin. Elastin-like recombinamers (ELRs) are ELPs produced using recombinant techniques and which can therefore be tailored for a specific application. One of the most widely used and studied characteristic structures in this field is the pentapeptide (VPGXG)_n. The structural disorder in ELRs probably arises due to the high content of proline and glycine in the ELR backbone, because both these amino acids help to keep the polypeptide structure of elastomers disordered and hydrated. Moreover, the recombinant nature of these systems means that different sequences can be designed, including bioactive domains, to obtain specific structures for each application. Some of these structures, along with their applications as IDPs that self-assemble into functional vesicles or micelles from diblock copolymer ELRs, will be studied in the following sections. The incorporation of additional order- and disorder-promoting peptide/protein domains, such as α-helical coils or β-strands, in the ELR sequence, and their influence on self-assembly, will also be reviewed. In addition, chemically cross-linked systems with controllable order–disorder balance, and their role in biomineralization, will be discussed. Finally, we will review different multivalent IDPs-based coatings and films for different biomedical applications, such as spatially controlled cell adhesion, osseointegration, or biomaterial-associated infection (BAI).     

Synthesis and Structural Studies of a Pentapeptide Sequence of Elastin. Poly (Val-Gly-Gly-Leu-Gly)

Abstract

Poly (Val-Gly-Gly-Leu-Gly), a polypeptide mimicking the physico-chemical properties of the glycine-rich regions of elastin, has been synthesized and studied both in solution and in the aggregated state. By comparison, also the conformation of different “monomeric” units has been investigated. The polymer showed increased disorder with respect to the “monomers”, the molecular conformation being accounted for by a more or less random collection of isolated β-turns. Nevertheless, in the solid state the polymer is able to adopt supramolecular structures reminiscent of those found for elastin.     

Molecular Simulation to Aid in the Understanding of the Aβ(1–42) Peptide of Alzheimer's Disease

Abstract

The Aβ(1–42) peptide of Alzheimer's disease was studied by molecular modeling. The coordinates of the peptide were experimentally generated from solution-NMR spectroscopy, and the conformations were energy minimized using a combination of connectivity-based iterative partial equalization of orbital electronegativity with the MM + force field.

There is a central folded domain in the Aβ peptide. This part is an apolar α-helix. The remaining residues form β-sheets. Aggregation requires that β-sheets interact by noncovalent bonding forces. The unsoluble, aggregated complexes are energetically stable and have ordered structures.

A perspective in drug research is to design compounds that inhibit the hydrophobic cores of the individual Aβ peptides, blocking so the associations between the β-strains.     

Unusual stability exhibited by (AT)XN12(AT)Y motif associated with high fetal hemoglobin levels

Abstract

Quasi-palindromic sequences (AT)_XN₁₂(AT)_Y present in HS2 (hypersensitive site 2) of the human β-globin locus are known to be significantly associated with increased fetal hemoglobin (HbF) levels. High HbF levels in some adults arise due to pathological conditions such as sickle cell disease and β-thalassemia. However, elevated levels of HbF are also associated with a reducing morbidity and mortality in patients with β-thalassemia and thus ameliorate the severity of the disease. Using gel-electrophoresis, ultraviolet (UV)-thermal denaturation, and circular dichroism (CD) techniques, we demonstrated that it exhibits a hairpin-duplex equilibrium. Intramolecular species (hairpin) were observed in both low and high salt concentrations in gel assay studies displaying the unusual stability of intramolecular species even at the high counter-ion concentration. The unusual stability of hairpin secondary structures was also demonstrated by the monophasic nature of the melting profiles for the oligonucleotides which persisted at low as well as high salt and oligomer concentrations. Change in CD spectra as a function of oligomer concentration indicates that the bimolecular duplex formation is selectively favored over monomolecular hairpin formation at and above 9 µM oligomer concentration. Thus, we hypothesize that imperfect inverted repeat sequence (AT)_XN₁₂(AT)_Y of HS2 of β-globin gene LCR forms the unusually stable hairpins which may result in the formation of a cruciform structure that may be recruited for binding by various nuclear proteins that could result in elevated HbF levels.

Communicated by Ramaswamy H. Sarma.     

Molecular Dynamics Study of Intrinsic Stability in Six RNA Terminal Loop Motifs

Abstract

Single stranded RNA molecules can assume a wide range of tertiary structures beyond the canonical A-form double helix. Certain sequences, termed motifs, are more common than a random distribution would suggest. The existence of such motifs can be rationalized in structural terms. In this study, we have investigated the intrinsic structural stability of RNA terminal loop motifs using multiple MD simulations in explicit water. Representative loops were chosen from the major tetraloop motifs, including also the U-turn motif. Not all loops retain their folded starting structure, but lowering the temperature to 277 K, or adding adjacent base pairs from the stem to which the motif is attached, helps stabilizing the folded loop structure.     

Radical-induced purine lesion formation is dependent on DNA helical topology

Abstract

Herein we report the quantification of purine lesions arising from gamma-radiation sourced hydroxyl radicals (HO^?) on tertiary dsDNA helical forms of supercoiled (SC), open circular (OC), and linear (L) conformation, along with single-stranded folded and non-folded sequences of guanine-rich DNA in selected G-quadruplex structures. We identify that DNA helical topology and folding plays major, and unexpected, roles in the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and 8-oxo-7,8-dihydro-2'-deoxyadenosine (8-oxo-dA), along with tandem-type purine lesions 5′,8-cyclo-2′-deoxyguanosine (5′,8-cdG) and 5′,8-cyclo-2′-deoxyadenosine (5′,8-cdA). SC, OC, and L dsDNA conformers together with folded and non-folded G-quadruplexes d[TGGGGT]₄ (TG4T), d[AGGG(TTAGGG)₃] (Tel22), and the mutated tel24 d[TTGGG(TTAGGG)₃A] (mutTel24) were exposed to HO^? radicals and purine lesions were then quantified via stable isotope dilution LC-MS/MS analysis. Purine oxidation in dsDNA follows L?>?OC???SC indicating greater damage towards the extended B-DNA topology. Conversely, G-quadruplex sequences were significantly more resistant toward purine oxidation in their unfolded states as compared with G-tetrad folded topologies; this effect is confirmed upon comparative analysis of Tel22 (～50% solution folded) and mutTel24 (～90% solution folded). In an effort to identify the accessibly of hydroxyl radicals to quadruplex purine nucleobases, G-quadruplex solvent cavities were then modeled at 1.33?Å with evidence suggesting that folded G-tetrads may act as potential oxidant traps to protect against chromosomal DNA damage.     

Strong Binding of Single-stranded DNA by Stem-loop Oligonucleotides

Abstract

We report that oligodeoxynucleotides which form stem-loop hairpin structures and which have pyrimidine-rich loops can form strong complexes with complementary single-stranded DNA sequences. Stem-loop oligonucleotides were constructed with a 25-nt T-rich loop and with variable Watson-Crick stems. The complexes of these oligomers with the sequence dA_gwere studied by thermal denaturation. Evidence is presented that the complexes are one-to-one, bimolecular complexes in which the pyrimidine loop bases comprise the outer strands in a pyr · pur · pyr triplex, in effect chelating the purine strand in the center of the loop. Melting temperatures for the loop complexes are shown to be up to 29 °C higher than Watson- Crick duplex of the same length. It is shown that the presence of a stem increases stability of the triplex relative to an analogous oligomer without a stem. The effect of stem length on the stability of such a complex is examined. Such hairpin oligomers represent a new approach to the sequence-specific binding of single-stranded RNA and DNA. In addition, the finding raises the possibility that such a complex may exist in natural RNA folded sequences.     

Nuclear Overhauser Effect and Computational Characterization of the β-Spiral of the Polypentapeptide of Elastin

Abstract

The structure of the elastin polypentapeptide, poly(VPGVG), was studied by nuclear Overhauser effect experiments using perdeuterated Val¹ and Val⁴ samples under the condition where intermolecular interactions are absent. More extensive interaction was found between the Val¹ γCH and Pro² βCH protons than between the Val⁴ γCH and Pro² βCH protons. The Val¹ γCH₃—Pro² βCH interaction does not occur within the same pentamer as previously shown experimentally and as expected from steric considerations. The results are incompatible with the presence of a random chain network in poly(VPGVG) at room temperature but are readily explicable in terms of interturn interactions in a β-spiral structure. More specifically, the results indicate that the β-spiral conformation with 2.9 pentamers/turn is more prevalent than that with 2.7 pentamers/turn. Using conformations developed by molecular mechanics calculations, molecular dynamics simulations were carried out to compare the relative energies of these two variants of this class of β-spiral structures. It was found in vacuo that the structure with 2.9 pentamers/turn is indeed more stable than that of 2.7 pentamers/turn by ~ 1 kcal/mole-pentamer.     

Morphology and fine structure of the gravid uterus of three hymenolepidid tapeworm species (Platyhelminthes: Cestoda)

Summary

The ultrastructure of the uterus in gravid proglottids of Hymenolepis citelli, Vampirolepis nana and Vampirolepis microstoma was examined using transmission and scanning electron microscopy. The cellular and subcellular structures were similar in all three species, consisting basically of a syncytial layer attached to a basal extracellular matrix. All nuclei were juxtaluminal and each contained a single large centrally located nucleolus and prominent masses of central and peripheral heterochromatin. The cytoplasm showed evidence suggesting a high level of protein synthesis and secretion. It consisted primarily of granular endoplasmic reticulum with moderately dilated cisternae; most cisternae were completely filled with an electron-lucent flocculent material, but others contained electrondense granules. Free ribosomes and mitochondria were also present. The apical plasma membrane and a small amount of enclosed cytoplasm were folded into long microlamellae that extended into the uterine lumen. Larger epithelial folds and villi consisting of folded portions of the entire epithelium projected into the uterine lumen. The uterine epithelium along with its basul extracellular matrix and underlying cellular parenchyma were folded into the lumen at several points, forming epitheliomesenchymal folds and villi that closely apposed many of the eggs.     

Nmr analyses of conformations of linear peptides in solution

Important aspects in detailed nmr analyses of the conformations of linear peptides are discussed using enkephalin and the α-mating factor of Saccharomyces cerevisiae as examples. The cationic, dipolar, and anionic forms in dimethyl sulfoxide solution may be identified by ir analyses. Because of the electrostatic interaction between the N- and C-terminal groups, the dipolar form of enkephalin takes the folded conformation, as well as extended conformation(s), in dimethyl sulfoxide solution. Such conformational equilibrium is responsible for anomalous temperature dependences and solvent-composition dependences of the amide and C^α proton chemical shifts. Active analogs, enkephalinamide and enkephalinol, take extended conformation(s) in solution. These opioid peptides probably take a specific active conformation upon binding with a receptor. For the α-mating factor and active peptide analogs in aqueous solution, a folded conformation with two βturn structures is responsible for the biological activity.     

The μ-selective Heptapeptide Opioid Dermorphin has Two Conformations Around Phe3 Ψ with no Head-to-tail Interaction. A Quantitative 2-D NMR and Molecular Modeling Analysis

Abstract

The μ opioid heptapeptide Dermorphin (DRM) is under 70% of trans forms for the Tyr⁵-Pro⁶ peptide bond in solution (CDC1₃/DMSO-d₆ 1/1 vol/vol). Variations of NOE integrals at 5 temperatures show apparent correlation times of 0.8 to 0.9 ns (at 280 K) in that mixed solvent. Four NOE between non-adjacent residues reveal a large population of folded structures. However, in trans DRM, 4 adjacent NOE Phe³/Gly⁴ can only be explained by an equilibrium between folded (ψ³ < 0) and extended (ψ³ > 0) conformations. Simulated annealing modeling gave about 60% (ψ³ < 0) and 40% (ψ³ > 0) of these conformer populations.

Trans DRM study and previous studies on the heptapeptide opioids, dermenkephalin (DREK) and deltorphin-I (δ selective), and DREK(1–4)-DRM(5–7) hybrid (μ selective), show in folded structures more backbone bending of the first 4 residues in the μ opioids than in the δ peptides. Also, the main difference between μ- and δ-opioid peptides is a large fraction of extended conformations in μ heptapeptides. Either bending of the N-terminus, or extension of the C-terminal part in μ-opioid heptapeptides prevent the head-to-tail interactions which allow δ-opioid peptides to bind selectively to the δ-opioid receptor.     

A Molecular Mechanics and Dynamics Study of Alternate Triple-Helices Involving the Integrase-Binding Site of the HIV-1 Virus and Oligonucleotides Having a 3′-3′ Internucleotide Junction

Abstract

Triple helix formation by oligonucleotides can be extended beyond polypurine tracts with the help of specially designed linkers. In this paper we focus our attention on the integrase- binding site of the HIV-1 virus located on the U5 LTR end which contains two adjacent purine tracts on opposite strands. Two alternate triple helices with a 3′-3′ junction in the third strand are considered:

5′-GGTTTTp3′-3′pTGTGT-5′ and 5′-GGAAAAp3′-3′pAGAGA-5′

The structural plausibility of these triplexes is investigated using molecular mechanics and dynamics simulations, both in vacuo and in aqua.

The non-isomorphism of the triplets in the GpT steps in the first sequence, gives rise to non canonical conformations in the torsion angles, hydration appears to be crucial for this triplex. Sugar puckers are predominantly South during in vacuo simulations while they tum East in aqua. In the simulation in aqua the triplexes are shrouded by an hydration shell, however, we have not been able to detect any permanent hydrogen bond bridge between DNA and water.

The solvation of ions as well as their radial distribution, appear to be relatively well behaved despite the artifacts known to be generated by the simulation procedure. The experimental feasibility of these structures is discussed.     

Reverse Relationship between α-Carbon Chirality and Helix Handedness in (αMe)Phe Peptides

Abstract

The crystal-state preferred conformations of two tripeptides, one tetrapeptide, and one pen- tapeptide, each containing a single residue of the chiral, C^α,α-disubstituted glycine C^α-methyl, C^α-benzylglycine [(αMe)Phe], have been determined by X-ray diffraction. The tripeptides are Z-L-(αMe)Phe-(Aib)₂-OH dihydrate and Z-Aib-D-(αMe)Phe-Aib-OtBu, the tetrapeptide is Z-(Aib)₂-D-(αMe)Phe-Aib-OtBu, and the pentapeptide is pBrBz-(Aib)₂-DL-(αMe)Phe-(Aib)₂-OtBu. While the two tripeptides are folded in a β-bend conformation, two such conformations are consecutively formed by the tetrapeptide. The pentapeptide adopts a regular 3₁₀-helix promoted by three consecutive β-bends. This study confirms the strong propensity of short peptides containing C^α-methylated α-aminoacids to fold into β-bends and 3₁₀-helical structures. Since Aib is achiral, the handedness of the observed bends and helices is dictated by the presence of the (αMe)Phe residue. In general, we have found that the relationship between (αMe)Phe chirality and helix handedness is opposite to that exhibited by protein aminoacids. A comparison with the preferred conformation of other extensively investigated C^α-methylated aminoacids is made.     

Protein Structures and Neutral Theory of Evolution

Abstract

The neutral theory of evolution is extended to the origin of protein molecules. Arguments are presented which suggest that the amino acid sequences of many globular proteins mainly represent “memorized” random sequences while biological evolution reduces to the “editing” these random sequences. Physical requirements for a functional globular protein are formulated and it is shown that many of these requirements do not involve strategical selection of amino acid sequences during biological evolution but are inherent also for typical random sequences. In particular, it is shown that random sequences of polar and unpolar amino acid residues can form α-helices and β-strands with lengths and arrangement along the chain similar to those in real globular proteins. These α- and β-regions in random sequences can form three-dimensional folding patterns also similar to those in real proteins. The arguments are presented suggesting that even the tight packing of side groups inside protein core do not require very strong biological selection of amino acid sequences either. Thus many structural features of real proteins can exist also in random sequences and the biological selection is needed mainly for the creation of active sites of proteins and for their stability under physiological conditions.     

Discrete analyses of protein dynamics

Abstract

Protein structures are highly dynamic macromolecules. This dynamics is often analysed through experimental and/or computational methods only for an isolated or a limited number of proteins. Here, we explore large-scale protein dynamics simulation to observe dynamics of local protein conformations using different perspectives. We analysed molecular dynamics to investigate protein flexibility locally, using classical approaches such as RMSf, solvent accessibility, but also innovative approaches such as local entropy. First, we focussed on classical secondary structures and analysed specifically how β-strand, β–turns, and bends evolve during molecular simulations. We underlined interesting specific bias between β–turns and bends, which are considered as the same category, while their dynamics show differences. Second, we used a structural alphabet that is able to approximate every part of the protein structures conformations, namely protein blocks (PBs) to analyse (i) how each initial local protein conformations evolve during dynamics and (ii) if some exchange can exist among these PBs. Interestingly, the results are largely complex than simple regular/rigid and coil/flexible exchange. Abbreviations N_eq number of equivalent

PB Protein Blocks

PDB Protein DataBank

RMSf root mean square fluctuations

Communicated by Ramaswamy H. Sarma     

Solid State and Solution Structure and Conformation of The Antiviral Acyclonucleoside 9-[4-Hydroxy-2-(hydroxymethyl)-butyl]guanine

Abstract

The title compound, 9-[4-hydroxy-2-(hydroxymethyl)-butyl]guanine (2HM-HBG), crystallizes in the triclinic space group P1 with two independent molecules and one water molecule in the asymmetric unit. The acyclic chain of one molecule is in the fully extended form, and the other partially folded. The orientation of this chain with respect to the base corresponds to the conformation syn in natural nucleosides. The conformations of the two molecules were compared with the solution conformation from an analysis of the ¹H-¹H vicinal coupling constants. The comportment of some acyclonucleosides in several enzyme systems is examined in relation to their existence in folded or extended forms.     

Human α-elastins: lipid-induced conformational changes

α-Elastins from young and old human aortas have been prepared and the interaction of these modified proteins with taurocholate, oleate, linoleate and palmitoleate has been studied by means of circular dichroism. Multiple conformational transitions were observed possibly involving, in addition to the aperiodic form, structures such as the β-bend and β-like forms. At the molecular level, a correlation between the aging of elastin and its interaction with lipids has been found that could be extended, at the macroscopic scale, to processes such as atherosclerosis and aging of the arterial wall.