**Structural Characterization of Ectodomain G Protein of Respiratory Syncytial Virus and Its Interaction with Heparan Sulfate: Multi-Spectroscopic and In Silico Studies Elucidating Host-Pathogen Interactions**

**Abu Hamza <sup>1</sup> , Abdus Samad <sup>1</sup> , Md. Ali Imam <sup>1</sup> , Md. Imam Faizan <sup>2</sup> , Anwar Ahmed <sup>3</sup> , Fahad N. Almajhdi 3,4 , Tajamul Hussain <sup>3</sup> , Asimul Islam 1,\* and Shama Parveen 1,\***


**Citation:** Hamza, A.; Samad, A.; Imam, M.A.; Faizan, M.I.; Ahmed, A.; Almajhdi, F.N.; Hussain, T.; Islam, A.; Parveen, S. Structural Characterization of Ectodomain G Protein of Respiratory Syncytial Virus and Its Interaction with Heparan Sulfate: Multi-Spectroscopic and In Silico Studies Elucidating Host-Pathogen Interactions. *Molecules* **2021**, *26*, 7398. https://doi.org/ 10.3390/molecules26237398

Academic Editors: Tanveer A. Wani, Seema Zargar and Afzal Hussain

Received: 11 November 2021 Accepted: 2 December 2021 Published: 6 December 2021

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**Abstract:** The global burden of disease caused by a respiratory syncytial virus (RSV) is becoming more widely recognized in young children and adults. Heparan sulfate helps in attaching the virion through G protein with the host cell membrane. In this study, we examined the structural changes of ectodomain G protein (edG) in a wide pH range. The absorbance results revealed that protein maintains its tertiary structure at physiological and highly acidic and alkaline pH. However, visible aggregation of protein was observed in mild acidic pH. The intrinsic fluorescence study shows no significant change in the λmax except at pH 12.0. The ANS fluorescence of edG at pH 2.0 and 3.0 forms an acid-induced molten globule-like state. The denaturation transition curve monitored by fluorescence spectroscopy revealed that urea and GdmCl induced denaturation native (N) ↔ denatured (D) state follows a two-state process. The fluorescence quenching, molecular docking, and 50 ns simulation measurements suggested that heparan sulfate showed excellent binding affinity to edG. Our binding study provides a preliminary insight into the interaction of edG to the host cell membrane via heparan sulfate. This binding can be inhibited using experimental approaches at the molecular level leading to the prevention of effective host–pathogen interaction.

**Keywords:** RSV; ectodomain G protein; heparan sulfate; protein–ligand interaction; fluorescence quenching; molecular docking; molecular dynamic simulation
