Biophysical studies of the interaction of hRSV Non-Structural 1 protein with natural flavonoids and their acetylated derivatives by spectroscopic techniques and computational simulations.

Human respiratory syncytial virus (hRSV) infections are one of the most causes of acute lower respiratory tract infections in children and elderly. The development of effective antiviral therapies or preventive vaccines against hRSV is not available yet. Thus, it is necessary to search for protein targets to combat this viral infection, as well as potential ways to block them. Non-Structural 1 (NS1) protein is an important factor for viral replication success since reduces the immune response by interacting with proteins in the type I interferon pathway. The influence of NS1 on the cell's immune response denotes the potential of its inhibition, being a possible target of treatment against hRSV infection. Here, it was studied the interaction of hRSV NS1 with natural flavonoids chrysin, morin, kaempferol, and myricetin and their mono-acetylated chrysin and penta-acetylated morin derivatives using spectroscopic techniques and computational simulations. The fluorescence data indicate that the binding affinities are on the order of 105 M-1, which are directly related to the partition coefficient of each flavonoid with Pearson's correlation coefficients of 0.76-0.80. The thermodynamic analysis suggests that hydrophobic interactions play a key role in the formation of the NS1/flavonoid complexes, with positive values of enthalpy and entropy changes. The computational approach proposes that flavonoids bind in a region of NS1 formed between the C-terminal α3-helix and the protein core, important for its biological function, and corroborate with experimental data revealing that hydrophobic contacts are important for the binding. Therefore, the present study provides relevant molecular details for the development of a possible new strategy to fight infections caused by hRSV.

Biophysical and flavonoid-binding studies of the G protein ectodomain of group A human respiratory syncytial virus.

The human Respiratory Syncytial Virus (hRSV) is the major causative agent of lower respiratory tract diseases in infants, young children and elderly. The membrane protein G is embedded in the viral lipid envelope and plays an adhesion function of the virus to host cells. The present study reports the production of the group A hRSV recombinant G protein ectodomain (edG) and its characterization of secondary structure and thermal unfolding by circular dichroism (CD), as well as the binding investigation of flavonoids quercetin and morin to this protein by fluorescent quenching. CD data reveal that edG is composed mostly of ß-structure and its melting temperature is of 325 K. Fluorescence quenching experiments of hRSV edG show that the dissociation constants for the flavonoids binding are micromolar and the binding affinity for the edG/quercetin complex is inversely dependent on rising temperature while is directly dependent for the edG/morin interaction. The thermodynamic parameters suggest that hydrophobic contacts are important for the edG/morin association while van der Waals forces and hydrogen bonds contribute to the stabilization of the edG/quercetin complex. Thus, data reported herein may contribute to the development of new treatment strategies that prevent the viral infection by hRSV.

Seasonality of viral respiratory infections in Southeast of Brazil: the influence of temperature and air humidity

Viruses are the major cause of lower respiratory tract infections in childhood and the main viruses involved are Human Respiratory Syncytial Virus (HRSV), Human Metapneumovirus (HMPV), Influenzavirus A and B (FLUA and FLUB), Human Parainfluenza Virus 1, 2 and 3 (HPIV1, 2 and 3) and Human Rhinovirus (HRV). The purposes of this study were to detect respiratory viruses in hospitalized children younger than six years and identify the influence of temperature and relative air humidity on the detected viruses. Samples of nasopharyngeal washes were collected from hospitalized children between May/2004 and September/2005. Methods of viral detection were RT-PCR, PCR and HRV amplicons were confirmed by hybridization. Results showed 54% (148/272) of viral positivity. HRSV was detected in 29% (79/272) of the samples; HRV in 23.1% (63/272); HPIV3 in 5.1% (14/272); HMPV in 3.3% (9/272); HPIV1 in 2.9% (8/272); FLUB in 1.4% (4/272), FLUA in 1.1% (3/272), and HPIV2 in 0.3% (1/272). The highest detection rates occurred mainly in the spring 2004 and in the autumn 2005. It was observed that viral respiratory infections tend to increase as the relative air humidity decreases, showing significant association with monthly averages of minimal temperature and minimal relative air humidity. In conclusion, viral respiratory infections vary according to temperature and relative air humidity and viral respiratory infections present major incidences it coldest and driest periods.