The binding of HIV-1 gp41 membrane proximal domain to its mucosal receptor, galactosyl ceramide, is structure-dependent

The peptide of HIV-1 envelope gp41 (a.a 628-683), referred to herein as P5, contains P1, a conserved galactose-specific lectin domain for binding the mucosal HIV-1-receptor, galactosyl ceramide (GalCer), as shown earlier, and a potential calcium-binding site (a.a 628-648). P1 contains contiguous epitopes recognized by the broadly neutralizing antibodies 2F5, 4E10, Z13. However, similar neutralizing antibodies could not be raised in animal model using immunogens based on these epitopes. We now show that the structure of both P5 and P1 peptides, as measured by circular dichroism, differs according to their environment: aqueous or lipidic, and as a function of calcium concentration. P5, but not P1, binds to calcium with a low binding affinity constant in the order of 2.5x10(4). Calcium binding results in a conformational change of P5, leading in turn to a decrease in affinity for GalCer. Hence, the affinity of the gp41-lectin site for the galactose harbored by the mucosal HIV-1 receptor GalCer is modulated by the peptide secondary and tertiary structure and the local environment. Therefore, definition of the conformation of this novel extended gp41 membrane proximal region, containing the conserved peptide P1 and the Ca(2+) binding site, could help designing an immunogen efficient at inducing neutralizing anti-HIV-1 antibodies.     

Influence of the position of the double bond in steroid substrates on the efficiency of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Δ4–Δ5-isomerase

Studies of the proton-transfer reaction by Pseudomonas testosteroni 3-oxo steroid Delta(4)-Delta(5)-isomerase with Delta(5(6))- and Delta(5(10))-steroid substrates demonstrate the importance of the position of the double bond for the efficiency of the isomerization process. Thus 3-oxo-Delta(5(6))-substrates have markedly high k(cat.) values, whereas those of 3-oxo-Delta(5(10))-substrates are very low and their apparent K(m) values approach equilibrium dissociation constants. The first step in the isomerization process is: [Formula: see text] which is governed by the k(-1)/k(+1) ratio and is shown to be very similar for the two classes of substrates (3-oxo-Delta(5(6))- and -Delta(5(10))-steroids). They therefore differ in the steps distal to the initial formation of the Michaelis-Menten complex. The use of the deuterated androst-5(6)-ene-3,17-dione substrate enabled us to calculate individual rate constants k(+1) and k(-1) as well as to determine the apparent rate-limiting step in the isomerization process. With the deuterated oestr-5(10)-ene-3,17-dione substrate, no significant isotope effect was observed suggesting that a different rate-limiting step may be operative in this isomerization process. Data are presented that indicate that under optimal concentrations of the efficient androst-5(6)-ene-3,17-dione substrate, the forward reaction for ES complex formation (as defined by k(+1)) is limited only by diffusion and the apparent K(m) does not approach the equilibrium constant, suggesting that the evolution of this enzyme has proceeded close to ;catalytic perfection'.     

Survival after intratumoral interleukin-2 treatment of 72 melanoma patients and response upon the first chemotherapy during follow-up

Systemic high-dose interleukin-2 (IL-2) treatment achieves long-term survival in a subset of advanced patients with melanoma. As we reported previously, intratumoral IL-2 induced complete local responses in more than 60% of melanoma patients. This study aimed to analyze the long-term outcome of 72 patients treated in two prior trials. Melanoma patients (49 stage III, 23 stage IV) with injectable metastases received intratumoral IL-2 injections thrice weekly at individually escalated doses (median duration, 6.5 weeks; median total IL-2 dose, 72 MIU; median number of injected metastases, 10). The observed 2-year overall survival rates were 95.5% for stage III patients with cutaneous metastases only (stage IIIB), 72% for those with combined cutaneous and lymph node involvement (stage IIIC), 66.7% for stage IV patients with disease limited to distant soft-tissue metastases (stage IV M1a), and 9.1% for those with visceral metastases (stage IV M1b and stage IV M1c). Thirty patients who reported recurrence of unresectable distant metastases subsequently received chemotherapy in the further course of disease and showed an overall response rate of 36.7% (16.7% complete responses, 20% partial responses). A high total dose of IL-2 and a dacarbazine/temozolomide-based chemotherapy regimen were variables correlated with a clinical response. In conclusion, patients with cutaneous metastasis without lymph node involvement in stage III and with soft-tissue metastasis without visceral involvement in stage IV showed unexpected favorable survival rates after intratumoral treatment with IL-2. Furthermore, the intratumoral IL-2 treatment seemed to be associated with increased complete and partial responses in subsequent chemotherapies.     

Epidermal RANKL controls regulatory T-cell numbers via activation of dendritic cells

Regulatory CD4(+)CD25(+) T cells are important in suppressing immune responses. The requirements for the maintenance of peripheral CD4(+)CD25(+) T cells remain incompletely understood. Receptor activator of NF-kappaB (RANK) and its ligand (RANKL; also known as CD254, OPGL and TRANCE) are key regulators of bone remodeling, mammary gland formation, lymph node development and T-cell/dendritic cell communication. Here we report that RANKL is expressed in keratinocytes of the inflamed skin. RANKL overexpression in keratinocytes resulted in functional alterations of epidermal dendritic cells and systemic increases of regulatory CD4(+)CD25(+) T cells. Thus, epidermal RANKL expression can change dendritic cell functions to maintain the number of peripheral CD4(+)CD25(+) regulatory T cells. Epidermal RANKL mediated ultraviolet-induced immunosuppression and overexpression of epidermal RANKL suppressed allergic contact hypersensitivity responses and the development of systemic autoimmunity. Therefore, environmental stimuli at the skin can rewire the local and systemic immune system by means of RANKL.     

Effect of peripherally administered ghrelin on gastric emptying and acid secretion in the rat

Ghrelin is a gut peptide that is secreted from the stomach and stimulates food intake. There are ghrelin receptors throughout the gut and intracerebroventricular ghrelin has been shown to increase gastric acid secretion. The aim of the present study was to examine the effects of peripherally administered ghrelin on gastric emptying of a non-nutrient and nutrient liquid, as well as, basal and pentagastrin-stimulated gastric acid secretion in awake rats. In addition, gastric contractility was studied in vitro. Rats equipped with a gastric fistula were subjected to an intravenous infusion of ghrelin (10-500 pmol kg(-1) min(-1)) during saline or pentagastrin (90 pmol kg(-1) min(-1)) infusion. After administration of polyethylene glycol (PEG) 4000 with 51Cr as radioactive marker, or a liquid nutrient with (51)Cr, gastric retention was measured after a 20-min infusion of ghrelin (500 pmol kg(-1) min(-1)). In vitro isometric contractions of segments of rat gastric fundus were studied (10(-9) to 10(-6) M). Ghrelin had no effect on basal acid secretion, but at 500 pmol kg(-1) min(-1) ghrelin significantly decreased pentagastrin-stimulated acid secretion. Ghrelin had no effect on gastric emptying of the nutrient liquid, but significantly increased gastric emptying of the non-nutrient liquid. Ghrelin contracted fundus muscle strips dose-dependently (pD2 of 6.93+/-0.7). Ghrelin IV decreased plasma orexin A concentrations and increased plasma somatostatin concentrations. Plasma gastrin concentrations were unchanged during ghrelin infusion. Thus, ghrelin seems to not only effect food intake but also gastric motor and secretory function indicating a multifunctional role for ghrelin in energy homeostasis.     

Expressed protein ligation. Method and applications.

The introduction of noncanonical amino acids and biophysical probes into peptides and proteins, and total or segmental isotopic labelling has the potential to greatly aid the determination of protein structure, function and protein-protein interactions. To obtain a peptide as large as possible by solid-phase peptide synthesis, native chemical ligation was introduced to enable synthesis of proteins of up to 120 amino acids in length. After the discovery of inteins, with their self-splicing properties and their application in protein synthesis, the semisynthetic methodology, expressed protein ligation, was developed to circumvent size limitation problems. Today, diverse expression vectors are available that allow the production of N- and C-terminal fragments that are needed for ligation to produce large amounts and high purity protein(s) (protein alpha-thioesters and peptides or proteins with N-terminal Cys). Unfortunately, expressed protein ligation is still limited mainly by the requirement of a Cys residue. Of course, additional Cys residues can be introduced into the sequence by site directed mutagenesis or synthesis, however, those mutations may disturb protein structure and function. Recently, alternative ligation approaches have been developed that do not require Cys residues. Accordingly, it is theoretically possible to obtain each modified protein using ligation strategies.     

Indene bioconversion by a toluene inducible dioxygenase of Rhodococcus sp. I24

Rhodococcus sp. I24 can oxygenate indene via at least three independent enzyme activities: (i) a naphthalene inducible monooxygenase (ii) a naphthalene inducible dioxygenase, and (iii) a toluene inducible dioxygenase (TID). Pulsed field gel analysis revealed that the I24 strain harbors two megaplasmids of 340 and 50 kb. Rhodococcus sp. KY1, a derivative of the I24 strain, lacks the 340 kb element as well as the TID activity. Southern blotting and sequence analysis of an indigogenic, I24-derived cosmid suggested that an operon encoding a TID resides on the 340 kb element. Expression of the tid operon was induced by toluene but not by naphthalene. In contrast, naphthalene did induce expression of the nid operon, encoding the naphthalene dioxygenase in I24. Cell free protein extracts of Escherichia coli cells expressing tidABCD were used in HPLC-based enzyme assays to characterize the indene bioconversion of TID in vitro. In addition to 1-indenol, indene was transformed to cis-indandiol with an enantiomeric excess of 45.2% of cis-(1S,2R)-indandiol over cis-(1R,2S)-indandiol, as revealed by chiral HPLC analysis. The K_m of TID for indene was 380 M. The enzyme also dioxygenated naphthalene to cis-dihydronaphthalenediol with an activity of 78% compared to the formation of cis-indandiol from indene. The K_m of TID for naphthalene was 28 M. TID converted only trace amounts of toluene to 1,2-dihydro-3-methylcatechol after prolonged incubation time. The results indicate the role of the tid operon in the bioconversion of indene to 1-indenol and cis-(1S,2R)-indandiol by Rhodococcus sp. I24.     

The voltage-gated calcium channel UNC-2 is involved in stress-mediated regulation of tryptophan hydroxylase

Migraine is an episodic pain disorder whose pathophysiology is related to deficiency of serotonin signaling and abnormal function of the P/Q-type calcium channel, CACNA1A. Because the relationship of the CACNA1A channel to serotonin signaling is unknown and potentially of therapeutic interest we have used genetic analysis of the Caenorhabditis elegans ortholog of this calcium channel, UNC-2, to help identify candidate downstream effectors of the human channel. By genetic dissection of the lethargic mutant phenotype of unc-2, we have established an epistasis pathway showing that UNC-2 function antagonizes a transforming growth factor (TGF)-beta pathway influencing movement rate. This same UNC-2/TGF-beta pathway is required for accumulation of normal serotonin levels and stress-induced modulation of tryptophan hydroxylase (tph) expression in the serotonergic chemosensory ADF neurons, but not the NSM neurons. We also show that transgenic expression of the migraine-associated Ca2+ channel, CACNA1A, in unc-2 animals can functionally substitute for UNC-2 in stress-activated regulation of tph expression. The demonstration that these evolutionarily related channels share a conserved ability to modulate tph expression through their effects on TGF-beta signaling provides the first specific example of how CACNA1A function may influence levels of the critical migraine neurotransmitter serotonin.     

Influenza A H5N1 clade 2.3.4 virus with a different antiviral susceptibility profile replaced clade 1 virus in humans in northern Vietnam

Background

Prior to 2007, highly pathogenic avian influenza (HPAI) H5N1 viruses isolated from poultry and humans in Vietnam were consistently reported to be clade 1 viruses, susceptible to oseltamivir but resistant to amantadine. Here we describe the re-emergence of human HPAI H5N1 virus infections in Vietnam in 2007 and the characteristics of the isolated viruses.

Methods and Findings

Respiratory specimens from patients suspected to be infected with avian influenza in 2007 were screened by influenza and H5 subtype specific polymerase chain reaction. Isolated H5N1 strains were further characterized by genome sequencing and drug susceptibility testing. Eleven poultry outbreak isolates from 2007 were included in the sequence analysis. Eight patients, all of them from northern Vietnam, were diagnosed with H5N1 in 2007 and five of them died. Phylogenetic analysis of H5N1 viruses isolated from humans and poultry in 2007 showed that clade 2.3.4 H5N1 viruses replaced clade 1 viruses in northern Vietnam. Four human H5N1 strains had eight-fold reduced in-vitro susceptibility to oseltamivir as compared to clade 1 viruses. In two poultry isolates the I117V mutation was found in the neuraminidase gene, which is associated with reduced susceptibility to oseltamivir. No mutations in the M2 gene conferring amantadine resistance were found.

Conclusion

In 2007, H5N1 clade 2.3.4 viruses replaced clade 1 viruses in northern Vietnam and were susceptible to amantadine but showed reduced susceptibility to oseltamivir. Combination antiviral therapy with oseltamivir and amantadine for human cases in Vietnam is recommended.