Aptamer-, heparin- or cocktail-based inhibition of S1-ACE2 protein complexes.

The Spike protein (S1) from the Severe acute respiratory syndrome 2 virus binds to angiotensin converting enzyme 2 (ACE2) receptor to initiate infection. Hence, antiviral therapeutic targeting the S1-ACE2 interface is of interest. Herein, we compare the inhibition efficacy of an aptamer to heparin or their cocktail, against wild-type (WT), Omicron, Delta, and Lambda S1-ACE2 complexes. The aptamer-protein complexes had the dissociation constant KD values in the 2-13 nM range. The aptamer half-maximal inhibitory concentration against WT S1-ACE was 17 nM, with the % inhibition in the 12-35% range. Several aptamer-S1 protein complexes were also stable at low pH with 60% inhibition. Despite the similarity in S1 sequences, the extent of inhibition (2-27%) with heparin was highly dependent on the type of S1 protein. More importantly, heparin did not inhibit the WT S1-ACE2 complex but was effective with mutants. The aptamer-heparin cocktail was less effective compared to aptamer or heparin, individually. Modelling data show that either a direct or proximal binding to RBD sites by aptamer or heparin prevents the ACE2 binding. Overall, heparin was as an effective inhibitor as aptamer against certain variants, and represents the more cost-effective neutralizing agent against emerging coronaviruses.

Electrochemical detection of the Fc-STAT3 phosphorylation and STAT3-Fc-STAT3 dimerization and inhibition.

Signal transducer and activator of transcription 3 (STAT3) protein is involved in regulatory functions in cell proliferation, differentiation and survival, and is linked to cancer phenotype and tumorigenesis. Towards developing new methodologies for screening STAT3 interactions, the electrochemical method based on the use of redox active protein was proposed. The electrochemical signal, due to the redox (ferrocene)-labeled STAT3 protein immobilized on a gold surface, was modulated due to protein dimerization with the unlabeled STAT3 molecule. The dramatic decrease in current density from 2.7 µA cm(-2) to 0.5 µA cm(-2) was observed following the STAT3-ferrocene-STAT3 dimerization. The electrochemical approach was further extended for screening the potential dimerization inhibitors. Previously published potent salicylic acid derivatives were the most promising candidates for inhibition of STAT3 dimerization in this assay. We expect that other SH2-containing proteins may be monitored by the proposed electrochemical method.