Protein Synthesis and Degradation
An Unbiased Mass Spectrometry Approach Identifies Glypican-3 as an Interactor of Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) and Low Density Lipoprotein Receptor (LDLR) in Hepatocellular Carcinoma CellsThe mechanism of LDL receptor (LDLR) degradation mediated by the proprotein convertase subtilisin/kexin type 9 (PCSK9) has been extensively studied; however, many steps within this process remain unclear and still require characterization. Recent studies have shown that PCSK9 lacking its Cys/His-rich domain can still promote LDLR internalization, but the complex does not reach the lysosome suggesting the presence of an additional interaction partner(s). In this study we carried out an unbiased screening approach to identify PCSK9-interacting proteins in the HepG2 cells' secretome using co-immunoprecipitation combined with mass spectrometry analyses.
Amyloid Precursor-like Protein 2 and Sortilin Do Not Regulate the PCSK9 Convertase-mediated Low Density Lipoprotein Receptor Degradation but Interact with Each OtherBackground It was reported that amyloid precursor-like protein 2 (APLP2) increases PCSK9-mediated low-density lipoprotein receptor (LDLR) degradation, and sortilin facilitates PCSK9 secretion. Results APLP2 or sortilin deficiency/overexpression in cells/mice did not affect LDLR degradation by PCSK9. However, APLP2 binds sortilin, and PCSK9 enhances their degradation. Conclusion APLP2/sortilin are not required for PCSK9 activity on LDLR, but their interaction may modulate APLP2 functions. Significance APLP2 and sortilin do not affect LDLR levels.
Isolation and Characterization of a Thionin Proprotein-processing Enzyme from BarleyBackground Thionins are produced as preproproteins, implicating the existence of a protease responsible for proteolytic processing. Results The barley subtilase BAJ93208 was found to be a strong candidate for the barley leaf thionin-processing enzyme. Conclusion A candidate processing enzyme for barley thionin proproteins has been identified. Significance The three-dimensional structure of the antimicrobial peptide protects it against proteolysis during processing.