The pandemic COVID-19 was caused by a novel Coronavirus-2 (SARS-CoV-2) that infects humans through the binding of glycosylated SARS-CoV-2 spike 2 protein to the glycosylated ACE2 receptor. The spike 2 protein recognizes the N-terminal helices of the glycosylated metalloprotease domain in the human ACE2 receptor. To understand the susceptibility of animals for infection and transmission, we did sequence and structure-based molecular interaction analysis of 16 ACE2 receptors from different mammalian species with SARS-CoV-2 spike 2 receptor binding domain. Our comprehensive structure analysis revealed that the natural substitution of amino acid residues Gln24, His34, Phe40, Leu79 and Met82 in the N-terminal α1 and α2 helices of the ACE2 receptor results in loss of crucial network of hydrogen-bonded and hydrophobic interactions with receptor binding domain of SARS-CoV-2 spike protein. Another striking observation is the absence of N-glycosylation site Asn103 in all mammals and many species, lack more than one N-linked glycosylation site in the ACE2 receptor. Based on the loss of crucial interactions and the absence of N-linked glycosylation sites we categorized Felis catus, Equus caballus, Panthera tigris altaica, as highly susceptible while Oryctolagus cuniculus, Bos Tauras, Ovis aries and Capra hircus as moderately susceptible species for infection. Similarly, the E. asinus, Bubalus bubalis, Canis lupus familiaris, Ailuropoda melaleuca and Camelus dromedarius are categorized as low susceptible with Loxodonta Africana, Mus musculus, Sus scrofa and Rattus rattus as least susceptible species for SARS-CoV-2 infection.
The pandemic COVID-19 caused by a novel coronavirus SARS-CoV-2 spread worldwide as a new public health emergency. The SARS-CoV-2 infects humans by binding to glycosylated ACE2 receptor present in the inner lining of the lungs, heart, intestine and kidney. The COVID spike 2 protein recognizes the ACE2 receptor at the N-terminal helices of the metalloprotease domain. The residues Gln24, Thr27, Lys31, His34, Glu37, Asp38, Tyr41, Gln42 from helix α1; Leu79, Met82, Tyr83 from helix α2 and Gln325, Glu329, Asn330, Lys353 from loop connecting β4 and β5 strands form a concave surface surrounded by four glycosylation sites Asn53, Asn90, Asn103 and Asn322 form interactions with the spike protein. However, no significant data on the susceptibility of animals for infection or transmission. Therefore, we performed the comparative protein-protein docking analysis using the crystal structure of spike protein and homology models of the ACE2 receptor from 16 commonly found mammalian species to understand the potential mode of spike binding. Our comprehensive sequence and structure-based interaction analysis revealed the natural substitution of amino acid residues Gln24, His34, Phe40 and Met82 in the N-terminal α1 and α2 helices results in loss of crucial network of hydrogen-bonded and hydrophobic interactions with spike 2 RBD domain. Besides, the absence of N-linked glycosylation site Asn103 in other mammals further reduces the binding affinity between spike and ACE2 receptor. Hence, these changes explain the differences in the susceptibility and host pathogenesis in other mammalian species.
Vibrio cholerae experiences a highly hostile environment at human intestine which triggers the induction of various heat shock genes. The hchA gene product of V. cholerae O395, referred to a hypothetical intracellular protease/amidase VcHsp31, is one such stress-inducible homodimeric protein. Our current study demonstrates that VcHsp31 is endowed with molecular chaperone, amidopeptidase and robust methylglyoxalase activities. Through site directed mutagenesis coupled with biochemical assays on VcHsp31, we have confirmed the role of residues in the vicinity of the active site towards amidopeptidase and methylglyoxalase activities. VcHsp31 suppresses the aggregation of insulin in vitro in a dose dependent manner. Through crystal structures of VcHsp31 and its mutants, grown at various temperatures, we demonstrate that VcHsp31 acquires two (Type-I and Type-II) dimeric forms. Type-I dimer is similar to EcHsp31 where two VcHsp31 monomers associate in eclipsed manner through several intersubunit hydrogen bonds involving their P-domains. Type-II dimer is a novel dimeric organization, where some of the intersubunit hydrogen bonds are abrogated and each monomer swings out in the opposite directions centering at their P-domains, like twisting of wet cloth. Normal mode analysis (NMA) of Type-I dimer shows similar movement of the individual monomers. Upon swinging, a dimeric surface of ~400Å2, mostly hydrophobic in nature, is uncovered which might bind partially unfolded protein substrates. We propose that, in solution, VcHsp31 remains as an equilibrium mixture of both the dimers. With increase in temperature, transformation to Type-II form having more exposed hydrophobic surface, occurs progressively accounting for the temperature dependent increase of chaperone activity of VcHsp31.
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