Structure and function of SARS-CoV spike glycoprotein fusion peptides

Abstract

The S2 domain of the spike (S) glycoprotein from Severe Acute Respiratory Syndrome (SARS)-coronavirus (CoV) is directly responsible for driving viral and host cell membrane fusion. Fusion peptides (FP), relatively hydrophobic segments located near the S2 domain N-terminus, play a crucial role in the fusion process. Although much information has been obtained in recent years on membrane fusion, many aspects of the molecular mechanism behind virus-host cell membrane fusion are not totally understood yet. In particular, many questions concerning the exact location and sequence of coronavirus fusion peptides as well as regarding the structure, dynamics, and topology of these molecules in lipid membranes still remain to be answered. In this project, we intend therefore to employ a wide variety of experimental and computational techniques to address these questions from different perspectives. Particularly, we are interested in a comparative structural and functional study of three membranotropic sequences, originally suggested as the putative fusion peptides of SARS-CoV S protein, and its corresponding non-fusogenic mutants to understand the role of each segment to the fusion reaction. It is also our interest to obtain a complete thermodynamic characterization of the interaction of the wild type peptides and their respective mutants with model membranes. Such information may also be determined via advanced molecular dynamics techniques, in which the free energy of binding, insertion, and peptide folding into lipid bilayers can be obtained. Knowledge of the structure and topology of these important membrane protein segments as well as the nature of the phospholipids-membrane peptides interactions are important to elucidate some of the steps of the complex and orchestrated membrane fusion mechanism mediated by viral glycoproteins. Additionally, besides being relevant to the stabilization and oligomerization of the S2 subunit, the transmembrane domain of the SARS-CoV S protein also plays an essential role in the fusion process. However, no structural explanation has been provided yet to elucidate the precise function of this domain. So, the additional purpose of this research proposal is to determine the structure, orientation, and oligomeric state of this peptide segment embedded into lipid model membranes. Thus, we aim to map out all the relevant regions of the S protein for the membrane fusion process at a molecular level, thereby building a detailed and comprehensive description of that phenomenon.