A fluorogenic peptide containing the processing site of human SARS corona virus S-protein: kinetic evaluation and NMR structure elucidation

A review on the cleavage priming of the spike protein on coronavirus by angiotensin-converting enzyme-2 and furin

The widespread antigenic changes lead to the emergence of a new type of coronavirus (CoV) called as severe acute respiratory syndrome (SARS)-CoV-2 that is immunologically different from the previous circulating species. Angiotensin-converting enzyme-2 (ACE-2) is one of the most important receptors on the cell membrane of the host cells (HCs) which its interaction with spike protein (SP) with a furin-cleavage site results in the SARS-CoV-2 invasion. Hence, in this review, we presented an overview on the interaction of ACE-2 and furin with SP. As several kinds of CoVs, from various genera, have at their S1/S2 binding site a preserved site, we further surveyed the role of furin cleavage site (FCS) on the life cycle of the CoV. Furthermore, we discussed that the small molecular inhibitors can limit the interaction of ACE-2 and furin with SP and can be used as potential therapeutic platforms to combat the spreading CoV epidemic. Finally, some ongoing challenges and future prospects for the development of potential drugs to promote targeting specific activities of the CoV were reviewed. In conclusion, this review may pave the way for providing useful information about different compounds involved in improving the effectiveness of CoV vaccine or drugs with minimum toxicity against human health.Communicated by Ramaswamy H. Sarma.

LDL-R promoting activity of peptides derived from human PCSK9 catalytic domain (153-421): design, synthesis and biochemical evaluation

BACKGROUND

High level of Low Density Lipoprotein-Cholesterol (LDL-C) in circulation in the blood is associated with an elevated risk of cardiovascular disease (CVD) and stroke. Currently the statin drugs which inhibit the enzyme HMG-CoA reductase responsible for cholesterol synthesis in the liver are very effective in lowering LDL-cholesterol. However these drugs are often associated with serious side effects particularly for ∼10-12% of cases. Therefore there is a need to develop non-statin based cholesterol reducing agents. Recently it was revealed that the secreted Proprotein Convertase Subtilisin Kexin 9 (PCSK9) binds with LDL-receptor (LDL-R) causing its degradation in the lysosome with the result of LDL-C accumulating in the blood. Thus PCSK9 has become an alternative target for development of non-statin cholesterol reducing agents. It is established that the catalytic domain of PCSK9 (aa153-421) and the EGF-A domain of LDL-R (aa314-355) are involved in the above bind leading to the reduction of LDL-R level and accumulation of LDL-C.

OBJECTIVE

The major goal of this study is to identify peptide/s from the catalytic domain of hPCSK9 that can block the binding of hPCSK9 and LDL-R and therefore can reduce LDL-R degradation leading to the clearance of LDL-C from the plasma.

RESULTS

Using 51 synthetic linear peptides (P1-P51) of 15aa long with 10 amino acids overlapping sequences spanning the entire catalytic segment of hPCSK9 (aa153-421), we identified two domains of hPCSK9 namely (aa323-358) and (aa365-384) that exhibited strong binding affinity towards synthetic EGF-A peptide. The results were based on mass spectrometry, fluorescence spectroscopy and native gel electrophoresis. Thus peptides containing the above segments in part (P35-P39 and P42-P47) exhibited LDL-R promoting activity when added exogenously to culture medium of growing human hepatic cells like HepG2 and HuH7. The effects were particularly significant with peptides P36, P37, P46 and P47. Interestingly, the first two peptides are present within the disulphide loop Cys(323)-Cys(358) and contain the key gain of function mutation D(374)/Y site while the last two peptides contain another disulphide bridge loop Cys(375)-Cys(378) and the second most potent gain of function mutation R(357)/H. Further studies revealed that S-S bridged cyclic loop peptide hPCSK9(365-384) exhibited the highest (∼3.5-fold) LDL-R promoting activity in both HepG2 and HuH7 when applied at 5 μM concentration level. This effect is completely abrogated when one of the Cys residues is substituted by Ala thereby preventing any S-S bond formation. This suggested its critical role in the bioactivity. It is proposed that LDL-R promoting activity of this and other selected PCSK9 catalytic peptides such as P36, P37, P46 and P47 are most likely mediated via intervention of PCSK9:LDL-R complex formation. Our findings may find useful application in future development of small molecule PCSK9 inhibitors for intervention of hypercholesterolemia and associated cardiovascular disease.

Dynamic cell patterning of photoresponsive hyaluronic acid hydrogels

Techniques to pattern cells on biocompatible hydrogels allow for the creation of highly controlled cell microenvironments within materials that mimic the physicochemical properties of native tissues. Such technology has the potential to further enhance our knowledge of cell biology and to play a role in the development of novel tissue engineering devices. Light is an ideal stimulus to catalyze pattern formation since it can be controlled spatially as well as temporally. Herein, we have developed and enhanced a hydrogel cell patterning strategy. It is based on photoactive caged RGDS peptides incorporated into a hyaluronic acid (HA) hydrogel, which can be subsequently activated with near-UV light to create cell-adhesive regions within an otherwise non-adhesive hydrogel. With this strategy, we have been able to pattern multiple cell populations-either in contact with one another or held apart-on an underlying chemically patterned HA hydrogel. Furthermore, the hydrogel cell pattern could be altered with time, even 2 weeks after initial seeding, to create additional adhesive regions to regulate the direction of cell growth and migration. These dynamic hydrogel cell patterns, created with a standard fluorescence microscope, were shown to be robust and lasted at least 3 weeks in vitro.

My road to Damascus: how I converted to the prohormone theory and the proprotein convertases

My desire as a young endocrinologist to improve my clinical skills through a better knowledge of hormone chemistry led me to serendipitous discoveries and unexpected horizons. The first discovery, published in 1967, revealed that peptide hormones are derived from endoproteolytic cleavages of larger precursor polypeptides. It was the foundation of the prohormone theory. Initially thought to apply to a few hormones, the theory rapidly extended to many proteins, including neuropeptides, neurotrophins, growth and transcription factors, receptors, extracellular matrix proteins, bacterial toxins, and viral glycoproteins. Its endoproteolytic activation mechanism has become a fundamental cellular process, affecting many biological functions. It implied the existence of specific endoproteolytic enzymes. These proprotein convertases were discovered in 1990. They have been shown to play a wide range of important roles in health and disease. They have opened up novel therapeutic avenues. Inactivation of PCSK9 to reduce plasma cholesterol is currently the most promising. To make this good thing even better, I recently discovered in a French Canadian family a potent PCSK9 (Gln152His) mutation that significantly lowers plasma cholesterol and should confer cardiovascular longevity. The discovery helped me to complete the loop: "From the bedside to the bench and back to the bedside."

Secretoneurin stimulates the production and release of luteinizing hormone in mouse L{beta}T2 gonadotropin cells

Secretoneurin (SN) is a functional secretogranin II (SgII)-derived peptide that stimulates luteinizing hormone (LH) production and its release in the goldfish. However, the effects of SN on the pituitary of mammalian species and the underlying mechanisms remain poorly understood. To study SN in mammals, we adopted the mouse LβT2 gonadotropin cell line that has characteristics consistent with normal pituitary gonadotrophs. Using radioimmunoassay and real-time RT-PCR, we demonstrated that static treatment with SN induced a significant increment of LH release and production in LβT2 cells in vitro. We found that GnRH increased cellular SgII mRNA level and total SN-immunoreactive protein release into the culture medium. We also report that SN activated the extracellular signal-regulated kinases (ERK) in either 10-min acute stimulation or 3-h chronic treatment. The SN-induced ERK activation was significantly blocked by pharmacological inhibition of MAPK kinase (MEK) with PD-98059 and protein kinase C (PKC) with bisindolylmaleimide. SN also increased the total cyclic adenosine monophosphate (cAMP) levels similarly to GnRH. However, SN did not activate the GnRH receptor. These data indicate that SN activates the protein kinase A (PKA) and cAMP-induced ERK signaling pathways in the LH-secreting mouse LβT2 pituitary cell line.

A novel enediynyl peptide inhibitor of furin that blocks processing of proPDGF-A, B and proVEGF-C

Background

Furin represents a crucial member of secretory mammalian subtilase, the Proprotein Convertase (PC) or Proprotein Convertase Subtilisin/Kexin (PCSK) superfamily. It has been linked to cancer, tumorgenesis, viral and bacterial pathogenesis. As a result it is considered a major target for intervention of these diseases.

Methodology/Principal Findings

Herein, we report, for the first time, the synthesis and biological evaluation of a newly designed potent furin inhibitor that contains a highly reactive beta-turn inducing and radical generating “enediynyl amino acid” (Eda) moiety. “Eda” was inserted between P1 and P1′ residues of hfurin^98–112 peptide, derived from the primary cleavage site of furin's own prodomain. The resulting hexadecapeptide derivative inhibited furin in vitro with IC₅₀ ∼40 nM when measured against the fluorogenic substrate Boc-RVRR-MCA. It also inhibited furin-mediated cleavage of a fluorogenic peptide derived from hSARS-CoV spike protein with IC₅₀ ∼193 nM. Additionally it also blocked furin-processing of growth factors proPDGF-A, B and VEGF-C that are linked to tumor genesis and cancer. Circular dichroism study showed that this inhibitor displayed a predominantly beta-turn structure while western blots confirmed its ability to protect furin protein from self degradation.

Conclusion/Significance

These findings imply its potential as a therapeutic agent for intervention of cancer and other furin-associated diseases.

Proteolytic processing of a precursor protein for a growth-promoting peptide by a subtilisin serine protease in Arabidopsis

Phytosulfokines (PSKs) are secreted, sulfated peptide hormones derived from larger prepropeptide precursors. Proteolytic processing of one of the precursors, AtPSK4, was demonstrated by cleavage of a preproAtPSK4-myc transgene product to AtPSK4-myc. Cleavage of proAtPSK4 was induced by placing root explants in tissue culture. The processing of proAtPSK4 was dependent on AtSBT1.1, a subtilisin-like serine protease, encoded by one of 56 subtilase genes in Arabidopsis. The gene encoding AtSBT1.1 was up-regulated following the transfer of root explants to tissue culture, suggesting that activation of the proteolytic machinery that cleaves proAtPSK4 is dependent on AtSBT1.1 expression. We also demonstrated that a fluorogenic peptide representing the putative subtilase recognition site in proAtPSK4 is cleaved in vitro by affinity-purified AtSBT1.1. An alanine scan through the recognition site peptide indicated that AtSBT1.1 is fairly specific for the AtPSK4 precursor. Thus, this peptide growth factor, which promotes callus formation in culture, is proteolytically cleaved from its precursor by a specific plant subtilase encoded by a gene that is up-regulated during the process of transferring root explants to tissue culture.