Screening coronavirus and human proteins for sialic acid binding sites using a docking approach

The initial step of interaction of some pathogens with the host is driven by the interaction of glycoproteins of either side via endcaps of their glycans. These end caps consist of sialic acids or sugar molecules. Coronaviruses (CoVs), including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), are found to use this route of interaction. The strength and spatial interactions on the single molecule level of sialic acids with either the spike (S) protein of SARS coronaviruses, or human angiotensin-converting enzyme 2 (ACE2) and furin are probed and compared to the binding modes of those sugar molecules which are present in glycans of glycoproteins. The protocol of using single molecules is seen as a simplified but effective mimic of the complex mode of interaction of the glycans. Averaged estimated binding energies from a docking approach result in preferential binding of the sialic acids to a specific binding site of the S protein of human coronavirus OC43 (HCoV-OC43). Furin is proposed to provide better binding sites for sialic acids than ACE2, albeit outweighed by sites for other sugar molecules. Absolute minimal estimated binding energies indicate weak binding affinities and are indifferent to the type of sugar molecules and the proteins. Neither the proposed best binding sites of the sialic acids nor those of the sugar molecules overlap with any of the cleavage sites at the S protein and the active sites of the human proteins. © 2021, AIMS Biophysics. All rights reserved.

Sequence-function correlation of the transmembrane domains in NS4B of HCV using a computational approach

An algorithm is applied to propose a sequence-function correlation of the transmembrane domains (TMDs) of the non-structural protein 4B (NS4B) of hepatitis C virus (HCV). The putative sequence of the TMDs is obtained using 20 available secondary structure prediction programs (SSPPs) with different lengths of the overall amino acid sequence of the protein as input. The results support the notion of four helical TMDs. Whilst the region of the first TMDs leaves room for speculation about an additional TMD, the other three TMDs are consistently predicted. Structural features and the role of each of the TMDs is proposed by applying pairwise sequence alignment using BLAST on the level (i) protein sequence alignment and consequent (ii) function-related alignment. Sequence identity with those TMDs of proteins involved in Ca-homeostasis and generation of replication vesicles, such as Nsp3 of corona viruses, murine coronavirus especially mouse hepatitis virus (MEW), middle east respiratory syndrome coronavirus (MERS), severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2, are suggested. Focusing the search on those proteins in particular and their TMDs playing an active role in their mechanism of function, such as transporters, pumps, viral channel forming protein Vpu of human immunodeficiency virus type 1 (HIV-1) and mediators, suggests TMDs 2 and 4 to have functional roles in NS4B, as well as additionally TMD1 and 3 in case of vesicle formation.