Efficient Fusion at Neutral pH by Human Immunodeficiency Virus gp41 Trimers Containing the Fusion Peptide and Transmembrane Domains

Human immunodeficiency virus (HIV) is membrane-enveloped, and an initial infection step is joining/fusion of viral and cell membranes. This step is catalyzed by gp41, which is a single-pass integral viral membrane protein. The protein contains an ∼170-residue ectodomain located outside the virus that is important for fusion and includes the fusion peptide (FP), N-helix, loop, C-helix, and viral membrane-proximal external region (MPER). The virion initially has noncovalent complexes between three gp41 ectodomains and three gp120 proteins. A gp120 contains ∼500 residues and functions to identify target T-cells and macrophages via binding to specific protein receptors of the target cell membrane. gp120 moves away from the gp41 ectodomain, and the ectodomain is thought to bind to the target cell membrane and mediate membrane fusion. The secondary and tertiary structures of the ectodomain are different in the initial complex with gp120 and the final state without gp120. There is not yet imaging of gp41 during fusion, so the temporal relationship between the gp41 and membrane structures is not known. This study describes biophysical and functional characterization of large gp41 constructs that include the ectodomain and transmembrane domain (TM). Significant fusion is observed of both neutral and anionic vesicles at neutral pH, which reflects the expected conditions of HIV/cell fusion. Fusion is enhanced by the FP, which in HIV/cell fusion likely contacts the host membrane, and the MPER and TM, which respectively interfacially contact and traverse the HIV membrane. Initial contact with vesicles is made by protein trimers that are in a native oligomeric state that reflects the initial complex with gp120 and also is commonly observed for the ectodomain without gp120. Circular dichroism data support helical structure for the N-helix, C-helix, and MPER and nonhelical structure for the FP and loop. Distributions of monomer, trimer, and hexamer states are observed by size-exclusion chromatography (SEC), with dependences on solubilizing detergent and construct. These SEC and other data are integrated into a refined working model of HIV/cell fusion that includes dissociation of the ectodomain into gp41 monomers followed by folding into hairpins that appose the two membranes, and subsequent fusion catalysis by trimers and hexamers of hairpins. The monomer and oligomer gp41 states may therefore satisfy dual requirements for HIV entry of membrane apposition and fusion.

The long-term outcomes of a cohort of Sri Lankan patients with ulcerative colitis: a retrospective study at two national referral centers and review of literature

BACKGROUND

Inflammatory bowel disease, especially ulcerative colitis, is increasing in many "non-Western" countries, including Sri Lanka. The aim was to evaluate long-term outcomes of ulcerative colitis in a Sri Lankan population.

METHODS

A retrospective cohort study was conducted at the gastroenterology clinics of the Colombo North Teaching Hospital, Ragama and the National Hospital of Sri Lanka, Colombo; the two major referral centers for ulcerative colitis. All cases had histological confirmation of ulcerative colitis. Three outcomes: colectomy, development of colorectal carcinoma, and death were assessed. Patients not attending the clinic during the previous 4 weeks, or their families, were contacted to obtain clinical details and survival status. In those who had died, the cause of death was confirmed from clinical records and death certificates.

RESULTS

Details of 348/425 (81.9%) patients with ulcerative colitis (mean age 45.6 [standard deviation {SD} 14.3] years, male/female ratio = 1.00:1.03) were available. The mean follow-up was 6.8 (SD 6.5) years. The cumulative colectomy rates at 1, 5, 10, and 15 years were 1.5%, 4.0%, 5.5%, and 9.3% respectively. The cumulative probability of colorectal cancer in this cohort after 10 and 15 years was 0.47% and 2.36% respectively. The cumulative survival rate after 1, 5, 10, and 15 years was 99.7%, 98.9%, 98.1%, and 94.5% respectively. Patients with pancolitis were more likely to have disease-related death (P = 0.05). Multivariate analysis (Cox proportional hazards model) showed that an older age at diagnosis was associated with long-term mortality (hazard ratio, 1.11; P = 0.001).

CONCLUSION

In this cohort, colectomy, colorectal carcinoma, and death rates were low, suggesting a relatively benign disease course for ulcerative colitis.

Clinically helpful rickettsial disease diagnostic IgG titers in relation to duration of illness in an endemic setting in Sri Lanka

Background

Although an initial IFA-IgG titer greater or equal to 1/64 or 1/128 is considered positive in presumptive diagnosis, in clinical practice in an endemic setting for rickettsioses in Sri Lanka, some patients with IFA-IgG titer of 1/128 for either spotted fever group (SFG) or scrub typhus (ST) did not respond to treatment.

Findings

To determine a clinically helpful diagnostic algorithm, IFA-IgG results of serologically confirmed treatment responders were analyzed in relation to duration of illness at sampling. Of 146 suspected SFG, 3 responders of 25 patients had titers ≤1/128 with < 7 days of illness while all 9 with titers ≥1/256 responded (false negative with 1/256 cutoff was 12%, false positive was 0%). For illness > 7 days, the false negative and positive rates were 4.3% (3/59) and 11.3% (6/53). Of 115 suspected ST, false negative and positive rates with ≥1/256 cutoff at <7 days of illness were 14.2% (2/14) and 0% (0/8) respectively while > 7 days, false negative and positive rates were 2% (1/51) and 0% (0/42).

Conclusions

For clinical decision making, duration of illness at sampling is important in interpreting serology results in an endemic setting. If sample is obtained ≤7 day of illness, an IgG titer of ≤1/128 requires a follow up sample in the diagnosis and > 7 days of illness, a single ≥1/256 titer is diagnostic for all ST and 90% of SFG.

Gluconeogenesis from glycerol by ketotic sheep pregnant with twins

The concentrations of glycerol and glucose in plasma, the entry rates of glycerol and glucose into the plasma pool and the production of glucose from glycerol were measured in four normal sheep pregnant with twins and in the same sheep after the induction of ketosis and after the oral administration of 3 ml/kg body-weight of glycerol in two doses six hours apart. After starvation there was a significant fall in the concentration of glucose and a rise in that of ketone bodies in the plasma. The rise in the concentration of glycerol was not significant. The divided oral dose of glycerol was followed by significant increases in the concentrations of glycerol and glucose and a significant fall in that of ketone bodies in plasma. After starvation, glucose and glycerol entry rates fell significantly from 42.0 +/- 3.5 to 18.1 +/- 1.4 mmol per hour and from 28.1 +/- 4.6 to 13.5 +/- 2.9 mmol per hour respectively. The amount of glucose formed from glycerol decreased from 5.4 +/- 1.2 to 3.0 +/- 0.5 mmol per hour. After a divided oral dose of glycerol, glycerol entry in the ketotic sheep rose significantly from 13.5 +/- 2.9 to 320 +/- 24.1 mmol per hour and glucose entry rate rose significantly from 18.1 +/- 1.4 to 71.5 +/- 10.1 mmol per hour. The amount of glucose produced from glycerol increased from 3.0 +/- 0.5 to 62.1 +/- 9.2 mmol per hour after the administration of glycerol. The oral dose of glycerol had no obvious effect on the clinical signs of induced ketosis.

The utilisation of glycerol by sheep

Increased but steady concentrations of glycerol and glucose in carotid, jugular and portal plasma of sheep were obtained between 2.5 and 3.5 h after the second of two oral doses of glycerol (2 and a ml/kg body weight with a 6 h interval between) and the concentration of glycerol in portal plasma was greater than in the other vessels. During the last hour of a 3.5 h continuous infusion of [14C]glycerol and [3H]glucose, ie, between 2.5 and 3.5 h after the second dose of glycerol, specific radioactivity(SRA) of glycerol and of [14C] an [3H] glucose were measured in plasma obtained from the three previously mentioned sites in dosed and undosed sheep. Although in dosed sheep the SRA of glycerol in portal plasma was lower than that in jugular plasma, the difference was such that the SRA in jugular plasma could be used to calculate entry rates and the rate of production of glucose from glycerol. Mean (+/- SE) glycerol entry rate in four fed sheep increased from 9.2 +/- 1.2 to 62.7 +/- 0.9 mg C/min after a divided oral dose of glycerol. Mean glucose entry rate increased from 29.0 +/0 3.4 to 58.3 +/- 7.6 mg C/min. The amount of glucose which was derived from glycerol increased from 5.4 +/- 1.6 to 35.5 +/- 3.7 mg C/min. This increase accounted for the increase in total glucose entry.

The effect of triamcinolone acetonide on plasma glucose and ketone concentration and on the total entry rate of glucose in twin pregnant hypoglycaemic ketotic sheep

Hypoglycaemic ketosis clinically resembling pregnancy toxaemia was induced by starvation in Clun Forest sheep pregnant with twins. Total glucose entry was measured by the continuous infusion of trace amounts of (2-3H) glucose before and after the induction of ketosis and 24 h after the intramuscular injection of the ketotic sheep with triamcinolone acetonide (0.5 mg/kg). The concentration of glucose in plasma fell significantly after the induction of ketosis and rose significantly after the injection of steroid. The total entry rate of glucose fell significantly after the induction of ketosis and rose, but no significantly, after steroid injection. It is suggested that the dose of steroid which was used may inhibit glucose utilisation by peripheral tissues. The induction of ketosis significantly reduced the duration of pregnancy but the steroid injection did not produce a significant additional effect.