Accessory proteins: a type of protein that cannot be neglected in coronaviruses

Abstract:

Coronaviruses (CoVs) are a group of positive-sense, single-stranded RNA viruses with the largest genome, most of which can spread across species and infect humans. Some of the pathogens in the group are causing major public health problems and seriously threatening human health. The full-length genome of the viruses is about 25—31 kb in length, encoding multiple nonstructural, structural proteins (S, E, M, and N) and accessory proteins. For most coronaviruses, their accessory proteins are not indispensable for viral replication, but they are often involved in pathogenesis in hosts and act as functional proteins. These accessory protein genes are located at the 3' end of the viral genomes. Expression of these genes can be regulated at transcription level by the transcription regulating sequence (TRS) which locates at the beginning of the genes or at translation level by the codon usage bias of the protein-coding sequences. The accessory proteins belong to trans-membrane protein and carry unique protein transport motifs. These characters play decisive role for the formation of unique topological structures and intracellular transport of the proteins, thus directly affect their functions. A summary of the latest classification and genome structure of coronaviruses was made in the beginning of the article; then roles, categorization, protein transport motifs, topological structures and codon usage bias of the accessory proteins were discussed individually and prospects of research in the field were foreseen as well, aiming to help understand the biological characteristics of this category of proteins.