Structural homology of the central conserved region of the attachment protein G of respiratory syncytial virus with the fourth subdomain of 55-kDa tumor necrosis factor receptor

The attachment protein G of respiratory syncytial virus (RSV) has a modular architecture. The ectodomain of the protein comprises a small folded conserved region which is bounded by two mucin-like regions. In this study, a sequence and structural homology is described between this central conserved region of RSV-G and the fourth subdomain of the 55-kDa tumor necrosis factor receptor (TNFr). The three-dimensional structures of RSV-G and human TNFr were previously determined with NMR spectroscopy and X-ray crystallography, respectively. The C-terminal part of both subdomains fold into a cystine noose connected by two cystine bridges with the same spacing between cysteine residues and the same topology. Although a general structural similarity is observed, there are differences in secondary structure and other structural features. Molecular Dynamics calculations show that the BRSV-G NMR structure of the cystine noose is stable and that the TNFr crystal structure of the cystine noose drifts towards the BRSV-G NMR structure in the simulated solution environment. By homology modelling a model was built for the unresolved N-terminal part of the central conserved region of RSV-G. The functions for both protein domains are not known but the structural similarity of both protein domains suggests a similar function. Although the homology suggests that the cystine noose of RSV-G may interfere with the antiviral and apoptotic effect of TNF, the biological activity remains to be proven.