3.4. Envelope protein (E protein)
The E proteins of SARS-CoV-2, SARS-CoV, and BatCoV RaTG13 are consisted of 75, 76, and 75 amino acids, respectively (Table 1). The identity and similarity percentages of the E protein of SARS-CoV-2 and SARS-CoV are 94.7 and 96.1 compared to 94.7 and 97.4 of Yashimito (2020) [12] (Table.2). The E proteins of the SARS-CoV-2 and the BatCoV RaTG13 are 100% identical and similar. The results strongly favor the bat origin of SARS-CoV-2 over the SARS-CoV origin. The E protein contains three domains; C-terminal, N- terminal, and trans-membrane with different functions for the virus and in the host cells [30].
The E protein plays different functions for the viral replication and for the interaction of the virus with the host organisms and cells such as the assembly of the virion envelope; suppression of the host cells stress responses; facilitation of the viral replication and vitality; and acting as ion channel to induce the release of the virions from the host cells [31-35].