5.1  Significance of the present work
The significance and innovation of the present work is that it proposes a sialic acid glycan binding function for the SARS-CoV-2 spike protein that has been largely neglected by other workers, apparently on the rationale that ACE-2 binding is the important first step in cell entry. Sites involved in the characteristic cap or knob of the spike protein appear partially persuasive in the light of their role as binding to host cells. There is a further possible site towards the base of the external part of the spike protein, which seems less likely by virtue of its position and weaker prediction. Interaction with sialic acid glycan with or without associated catalytic activity would be consistent with such functions observed in many respiratory and alimentary tract viruses, and not least in many or most other coronaviruses, and so such a function must be important to these viruses. On these grounds, it may be a target for therapeutic agents against SARS-CoV-2, particularly perhaps preventatives as well as means of impeding spread from lung cell to lung cell, and an exposed target for antibodies raised by synthetic vaccines. Although other authors have recently touched on such a glycan binding ability in SARS (as discussed in this paper above and particularly below), it has not been to the present author's knowledge analyzed in comparable detail and do not appear to relate to the same site. Nor do they propose a general prediction method for sialic acid glycan binding as described in the present paper. Of course, in the present paper this is still a prediction and not an experimental result, but it will hopefully encourage experimental researchers to investigate the glycan binding properties of SARS-CoV-2 more extensively. A further innovative feature is that predictive method, which is expected to be worthy of investigation for the proteins of other viruses and even of other organisms. Like many predictive methods in bioinformatics it is not perfect, i.e. there are false positives and false negatives in prediction, so it is actually conceivable that the method is useful even if it is not correct in the particular case of SARS-CoV-2. In that sense, it may emerge as the more important contribution.