The article from Minnesota/North Carolina continues:
'Third, residues 455, 486 and 494 are leucine, phenylalanine and serine in 2019-nCoV RBD, respectively (corresponding to residues 442, 472, and 480 in SARS-CoV, respectively). Based on our previous structural analysis, these three residues in SARS-CoV RBD play significant roles, albeit not as dramatic as residues 479 and 487, in ACE binding. More specifically, Tyr442 of human and civet SARS-CoV RBDs provides unfavorable interactions with hotspot-31 on human ACE2 (this residue has been mutated to Phe442 in the optimized RBD); Leu455 of 2019-nCoV RBD provides favorable interactions with hotspot-31, hence enhancing viral binding to human ACE2. Leu472 of human and civet SARS-CoV RBDs provides favorable support for hotspot-31 on human ACE2 through hydrophobic interactions with ACE2 residu Met82 and several other hydrophobic residues (this residue has been mutated to Phe472 in the optimized RBD); Phe486 of 2019-nCoV RBD provides even more support for hotspot-31, hence also enhancing viral binding to human ACE2. Asp480 of human and civet SARS-CoV Rbds provides favorable support for hotspot-353 on human ACE2 through a neighboring tyrosine (this residue remains as an aspartate in the optimized RBD); Ser494 in 2019-nCoV still provides positive support for hotspot-353, but the support is not as favorable as provided by Asp480. Overall, Leu455, Phe486 and Ser494 of 2019-nCoV RBD support that 2019-nCoV recognizes human ACE2 and infects human cells.
Last, having analyzed the interactions between 2019-nCoV RBD and human ACE2, how does 2019-nCoV RBD interact with putative ACE2 receptor orthologues from other animal species? Compared to human ACE2, both hotspot-31 and hotspot-353 on civet ACE2 have changed significantly (Fig.4). Specifically, residue 31 of civet ACE2 becomes a threonine, which can no longer form a salt bridge with Glu35; residue 38 of civet ACE2 becomes a glutamate, which forms a strong bifurcated salt bridge with Lys353 and no longer needs strong support from neighboring residues. A previously designed SARS-CoV RBD is optimal for binding to civet ACE2 (Fig 1B, 4B). In this designed RBD, Tyr442 forms a hydrogen bond with Thr31 of civet ACE2, and Gly480 does not provide unneeded support for hotspot-353. Furthermore, in the designed RBD, Thr487 provides limited but helpful support for hotspot-353. Here we constructed a structural model for the complex of 2019-nCoV RBD and civet ACE2. Based on this model, Phe486 of 2019-nCoV RBD forms moderately unfavorable interaction with the polar side chain of Thr82 of civet ACE2, and Leu455 and Gln493 would lose favorable interactions with civet ACE2 but they would be still compatible with civet ACE2. Thus, 2019-nCoV likely still uses civet ACE2 as its receptor, although it appears that 2019-nCoV RBD has not evolved adaptively for civet ACE2 binding.
Moreover, 2019-nCoV likely does not use mouse or rat ACE2 as its receptor because mouse or rat ACE2 contains a histidine at position 353, which does not fit into the virus-receptor interact as well as a lysine does. 2019-nCoV RBD likely recognizes ACE2 from pigs, ferrets, cats, orangutans, monkeys and humans with similar efficiency, because these ACE2 molecules are identical or similar in the critical virus-binding residues. The situation involving bat ACE2 is complex because of the diversity of bat species. Based on the sequence of ACE2 from Rhinolophus sinicus bats (which can be recognized by bat SARS-CoV strain Rs3367), 2019-nCoV RBD likely also recognizes bat ACE2 as it receptor. Overall, 2019-nCoV likely recognizes ACE2 orthologues from a diversity of species, except for mouse and rat ACE2 (which should be poor receptors fo 2019-nCoV).
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Thus, 2019-nCoV evolution in patients should be closely monitored for the emergence of novel mutations at the 501 position (to a lesser extent, also the 494 position).'
