Coronavirus- An Overview


Coronaviruses are a large group of viruses that can infect humans and animals. They are named after the crown-like spikes that protrude from their surface, which are called spike (S) proteins. These proteins are responsible for attaching to and entering host cells.

Coronaviruses belong to the family Coronaviridae, which is divided into four genera: alpha, beta, gamma, and delta. Human coronaviruses (HCoVs) are mainly classified into alpha and beta genera. Some examples of HCoVs are 229E, NL63, OC43, HKU1, SARS-CoV, MERS-CoV, and SARS-CoV-2.

Coronaviruses have a spherical shape and a diameter of about 120 to 160 nanometers. They have an envelope made of a lipid bilayer that surrounds a nucleocapsid. The nucleocapsid is a helical structure that contains the viral genome and a protein called nucleocapsid (N) protein.

The viral genome is a single-stranded positive-sense RNA molecule that ranges from 27 to 32 kilobases in length. It encodes several proteins that are involved in viral replication, transcription, and assembly. The most important ones are the replicase gene products, which form a complex that synthesizes new viral RNA molecules.

The viral envelope also contains two other proteins: membrane (M) protein and envelope (E) protein. The M protein is the most abundant one and serves as a matrix that supports the shape of the virus and interacts with the nucleocapsid. The E protein is a small protein that plays a role in virus assembly and release.

Some coronaviruses, such as OC43 and HKU1, have a fourth protein on their envelope called hemagglutinin-esterase (HE) protein. This protein has two functions: it binds to sialic acid receptors on host cells and it cleaves ester bonds on the surface of host cells.

The structure of coronaviruses is important for understanding how they infect and cause disease in humans. The S protein determines the tropism and specificity of the virus for different cell types and organs. The N protein protects the viral RNA from degradation and regulates its transcription. The M and E proteins facilitate the assembly and release of new virions. The HE protein enhances the attachment and entry of some coronaviruses into host cells.