Display omitted •Only few ACE2 residues are strongly bound to Corona virus spike RBDs.•SARS-CoV-2 RBDs have strong attractive interactions with just two ACE2 residues.•Pull off force for SARS-CoV RBD from ACE2 is higher than that for SARS-CoV-2.•Attachment of ACE2 with both Corona viruses result in increased stiffness of ACE2.•Change in stiffness of ACE2 is six times higher for SARS-CoV-2 than SARS-CoV. The SARS-CoV-2 coronavirus (COVID-19) that is causing the massive global pandemic exhibits similar human cell invasion mechanism as the coronavirus SARS-CoV, which had significantly lower fatalities. The cell membrane protein Angiotensin-converting enzyme 2 (ACE2) is the initiation point for both the coronavirus infections in humans. Here, we model the molecular interactions and mechanical properties of ACE2 with both SARS-CoV and COVID-19 spike protein receptor-binding domains (RBD). We report that the COVID-19 spike RBD interacts with ACE2 more strongly and at only two protein residues, as compared to multi-residue interaction of the SARS-CoV. Although both coronaviruses stiffen the ACE2, the impact of COVID-19 is six times larger, which points towards differences in the severity of the reported respiratory distress. The recognition of specific residues of ACE2 attachments to coronaviruses is important as the residues suggest potential sites of intervention to inhibit attachment and subsequent entry of the COVID-19 into human host cells