**3. Molecular biology of** *SARS-CoV-2*

*SARS-CoV-2* belongs to beta coronaviruses and has a round or elliptic form, with an approximate diameter of 60–140 nm. The virus genome is an around 30 Kb positive-sense, single-stranded RNA, which encodes four structural proteins including S protein (Spike), E protein (Envelope), M protein (Membrane), and N protein (Nucleocapsid), and several accessory proteins or nonstructural proteins, namely, NSP1 to NSP16 [11]. S protein is 150 kDa, acts as an anchor on the virus envelope, and consists of three domains including the outer N-terminal domain having unit S1 and S2, a cytoplasmic C-terminal domain, and a transmembrane domain. M protein is 25–35 kDa, a transmembrane glycoprotein type III and the most abundant protein on the surface of the virus. Based on the bioinformatics analysis, the protein can play a role in the virus entry into the host cell and its RNA maturation.


*Evaluation of Drug Repositioning by Molecular Docking of Pharmaceutical Resources… DOI: http://dx.doi.org/10.5772/intechopen.101395*

#### **Table 1.**

*Description of various roles of non-structural proteins from SARS-CoV-2.*

N protein is a 43–50 kDa nucleocapsid structural protein and has a vital role in attaching and assembling the virus genome to the matrix of the ribonucleoprotein. The E protein is 8.4–109 kDa and is recognized as a small hydrophobic protein. The protein contributes to viroporin activity, virus assembling, and the virus budding process. Based on the results of several studies, the nonstructural proteins encoded by genes positioned within the 5′-region of the virus genome, have a wide range of roles from host translation inhibition by NS1 to viral replication-transcription NS4 [12, 13]. The main roles of the known nonstructural proteins of *SARS-CoV-2* are summarized in **Table 1**.
