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The entry of the SARS-CoV2 virus in human cells is mediated by the binding of its surface spike protein to the human Angiotensin-Converting Enzyme 2 (ACE2) receptor. A 23 residues long helical segment (SBP1) at the binding interface of human ACE2 interacts with viral spike protein and therefore, has generated considerable interest as a recognition element for virus detection. Unfortunately, emerging reports indicate that the affinity of SBP1 to the receptor-binding domain (RBD) of the spike protein is much lower than that of the ACE2 receptor itself. Here, we examine the biophysical properties of SBP1 to reveal factors leading to its low affinity for the spike protein. While SBP1 shows good solubility (solubility > 0.8 mM), CD spectroscopy shows that it is mostly disordered with some anti-parallel beta-sheet content, and no helicity. The helicity is substantial (> 20%) only upon adding high concentrations (≥ 20% v/v) of 2,2,2-trifluoroethanol, a helix-promoter. Fluorescence correlation spectroscopy and single molecule photobleaching studies show that the peptide oligomerizes at concentrations > 50 nM. We hypothesized that mutating the hydrophobic residues (F28, F32, and F40) of SBP1 which do not directly interact with the spike protein to alanine would reduce peptide oligomerization without affecting its spike binding affinity. While the mutant peptide (SBP1 mod ) shows substantially reduced oligomerization propensity, it does not show improved helicity. Our study shows that the failure of efforts so far to produce a short SBP1 mimic with a high affinity for the spike protein is not only due to the lack of helicity, but also due to the heretofore unrecognized problem of oligomerization.

Cyclin-dependent-kinases (CDKs) are essential for cell cycle progression. While dependence of CDK activity on Cyclin levels is established, molecular mechanisms that regulate their binding are less studied. Here, we show that CDKl:Cyclin-B interactions are regulated by acetylation, which was hitherto unknown. We demonstrate that cell cycle dependent acetylation of the evolutionarily conserved catalytic lysine in CDK1 or eliminating its charge state abrogates Cyclin-B binding. Opposing activities of SIRT1 and P300 regulate acetylation, which marks a reserved pool of CDK1. Our high resolution structural analyses into the formation of kinase competent CDK1: Cyclin-B complex have unveiled long-range effects of catalytic lysine in configuring the CDK1 interface for Cyclin-B binding. Cells expressing acetylation mimic mutant of Cdc2 in yeast are arrested in G2 and fail to divide. Thus, by illustrating cell cycle dependent deacetylation as a determinant of CDK1:Cyclin-B interaction, our results redefine the current model of CDK1 activation and cell cycle progression.

Onkaramurthy et al.: Herbal Formulations for the Management of Varicose VeinsVaricose vein is one of the common vascular diseases, in which veins become widened, bulged and twisted. Development of drug to combat varicose vein is a challenging task due to complex nature of the disease and non-availability of specific animal model system. In this context, relevant experimental models were developed and polyherbal formulations HVVL-041702 a liniment intended for topical use (200 µl/ animal) and HVVT-041701 a granule intended for oral use (250 mg/kg body weight, orally) were evaluated. In vitro elastase inhibition assay was carried out using the human leukocyte elastase enzyme. Ex vivo venotonic activity was performed in isolated rat vena cava. In vivo anti-inflammatory, analgesic and anti-edemagenic activity were carried out in Wistar rats. Along with the aforementioned activities, HVVT-041701 was also evaluated for chronic venous insufficiency. Both the formulations showed elastase inhibition, venotonic, antiinflammatory, analgesic and anti-edemagenic activities. HVVT-041701 was also effective in ameliorating chronic venous insufficiency by decreasing the venous pressure. Both the formulations showed beneficial effects in the management of varicose veins by improving the tonicity, venous insufficiency and vascular hyper permeability which are the pathologic hallmark of varicose veins.

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