The severe acute respiratory syndrome coronavirus (SARS-CoV) envelope spike (S) glycoprotein, a Class I viral fusion protein. is responsible for the fusion between the membranes of the virus and the target cell. In order to gain new insight into the protein membrane alteration leading to the viral fusion mechanism, a peptide pertaining to the putative pre-transmembrane domain (PTM) of the S glycoprotein has been studied by infrared and fluorescence spectroscopies regarding its structure, its ability to induce membrane leakage, aggregation, and fusion, as well as its affinity toward specific phospholipids. We demonstrate that the SARS-CoV PTM peptide binds to and interacts with phospholipid model membranes, and, at the same time, it adopts different conformations when bound to membranes of different compositions. As it has been already suggested for other viral fusion proteins such as HIV gp41, the region of the SARS-CoV protein where the PTM peptide resides could be involved in the merging of the viral and target cell membranes working synergistically with other membrane-active regions of the SARS-CoV S glycoprotein to heighten the fusion process and therefore might be essential for the assistance and enhancement of the viral and cell fusion process.