Publications

Angiotensin converting enzyme 2 (ACE2) works in the renin angiotensin aldosterone system to decrease circulating levels of angiotensin II by removing the C-terminal phenylalanine and converting it to angiotensin (1-7). In addition, ACE2 has received increased interest in research due to its role in COVID-19 pathogenesis, as the binding site and cell entry gate for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While ACE2 inhibitors have been primarily used as pharmacological tools to study the renin-angiotensin system, small molecule ACE2 enhancers (aka activators) are highly desired because of their hypothesized therapeutic potential. This study was designed to identify peptide-based enhancers of ACE2. First, binding of human recombinant ACE2 to all possible tripeptides composed of the 20 proteinogenic amino acids, was evaluated using a proprietary immunofluorescence-based peptide microarray. Binding of 6xHis-tagged ACE2 to the 8000 tripeptides immobilized on a microchip was evaluated at 10 µg/ml and 100 µg/ml concentrations of the peptidase using a DyLight680-conjugated anti-6xHis-tag antibody. Hemagglutinin (HA) immobilized on the microchip served as a positive control peptide in the microarray and it was tracked using a DyLight800-conjugated anti-HA antibody. The read-out was performed with an Innopsys InnoScan 710-IR Microarray Scanner at scanning gains of 50/10 (red/green). In the result of the microarray a number of tripeptides were identified as potential ACE2 binders. Among them, 22 tripeptides were selected to represent several the most pronounced binders as well as a number of structurally similar tripeptides that did not show appreciable binding to ACE2 to serve as negative control. The effect of the selected peptides (at 1, 10 and 100 µM) on activity of human recombinant ACE2 was tested in a continuous enzymatic assay using a fluorogenic substrate. Contrary to our expectation, none of the peptides affected the activity of ACE2 in a significant manner. These results suggest that the selected peptides do not alter activity of ACE2, but they do not exclude the possibility that some of the peptides may still bind to the peptidase. Our subsequent experiments will apply differential scanning fluorometry (DSF) to determine whether these peptides physically interact with recombinant ACE2.

While aggregation-prone proteins are known to accelerate aging and cause age-related diseases, the cellular mechanisms that drive their cytotoxicity remain unresolved. The orthologous proteins MOAG-4, SERF1A, and SERF2 have recently been identified as cellular modifiers of such proteotoxicity. Using a peptide array screening approach on human amyloidogenic proteins, we found that SERF2 interacted with protein segments enriched in negatively charged and hydrophobic, aromatic amino acids. The absence of such segments, or the neutralization of the positive charge in SERF2, prevented these interactions and abolished the amyloid-promoting activity of SERF2. In protein aggregation models in the nematode worm Caenorhabditis elegans, protein aggregation and toxicity were suppressed by mutating the endogenous locus of MOAG-4 to neutralize charge. Our data indicate that MOAG-4 and SERF2 drive protein aggregation and toxicity by interactions with negatively charged segments in aggregation-prone proteins. Such charge interactions might accelerate primary nucleation of amyloid by initiating structural changes and by decreasing colloidal stability. Our study points at charge interactions between cellular modifiers and amyloidogenic proteins as potential targets for interventions to reduce age-related protein toxicity.

Multiple starvation-induced, high-affinity nutrient transporters in yeast function as receptors for activation of the protein kinase A (PKA) pathway upon re-addition of their substrate. We now show that these transceptors may play more extended roles in nutrient regulation. The Gap1 amino acid, Mep2 ammonium, Pho84 phosphate and Sul1 sulfate transceptors physically interact in vitro and in vivo with the PKA-related Sch9 protein kinase, the yeast homolog of mammalian S6 protein kinase and protein kinase B. Sch9 is a phosphorylation target of TOR and well known to affect nutrient-controlled cellular processes, such as growth rate. Mapping with peptide microarrays suggests specific interaction domains in Gap1 for Sch9 binding. Mutagenesis of the major domain affects the upstart of growth upon the addition of L-citrulline to nitrogen-starved cells to different extents but apparently does not affect in vitro binding. It also does not correlate with the drop in L-citrulline uptake capacity or transceptor activation of the PKA target trehalase by the Gap1 mutant forms. Our results reveal a nutrient transceptor–Sch9–TOR axis in which Sch9 accessibility for phosphorylation by TOR may be affected by nutrient transceptor–Sch9 interaction under conditions of nutrient starvation or other environmental challenges.