title: LDL-R promoting activity of peptides derived from human PCSK9 catalytic domain (153-421): design, synthesis and biochemical evaluation.
abstract: 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.
authors: Interdisciplinary School of Health Sciences Unit, Faculty of Health Science, U Ottawa, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada.
authors: Rasha H
authors: RH
authors: Alghamdi
authors: Interdisciplinary School of Health Sciences Unit, Faculty of Health Science, U Ottawa, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada.
authors: Paul
authors: P
authors: O'Reilly
authors: Interdisciplinary School of Health Sciences Unit, Faculty of Health Science, U Ottawa, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada.
authors: Chunyu
authors: C
authors: Lu
authors: Interdisciplinary School of Health Sciences Unit, Faculty of Health Science, U Ottawa, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada.
authors: James
authors: J
authors: Gomes
authors: Lipoprotein Receptor Biology Laboratory, Department of Pathology and Laboratory Medicine, University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, ON K1Y 4W7, Canada.
authors: Thomas A
authors: TA
authors: Lagace
authors: Interdisciplinary School of Health Sciences Unit, Faculty of Health Science, U Ottawa, 451 Smyth Road, Ottawa, ON K1H 8M5, Canada; Chronic Disease Program, Ottawa Hospital Research Institute, U Ottawa, 725 Parkdale Ave, Ottawa, ON K1Y4E9, Canada. Electronic address: abasa2@uottawa.ca.
authors: Ajoy
authors: A
authors: Basak
mesh_terms: D055162:Biocatalysis; D020134:Catalytic Domain; D015195:Drug Design; D056945:Hep G2 Cells; D006801:Humans; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism*; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000737:chemistry / Q000378:metabolism*; D011973:Receptors, LDL / Q000097:blood / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D010455:Peptides; D011973:Receptors, LDL; C472125:PCSK9 protein, human; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases
keywords: Cholesterol lowering agents; Epidermal Growth Factor-A (EGF-A); Fluorescence quenching; Low Density Lipoprotein receptor (LDL-R); PCSK9 inhibitors; Proprotein Convertase Subtilisin Kexin 9 (PCSK9)