Browsing by Subject "Hydrolase"

Now showing 1 - 2 of 2
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    Lysosomal Acid Lipase Hydrolyzes Retinyl Ester and Affects Retinoid Turnover
    (American Society for Biochemistry & Molecular Biology, 2016-08-19) Grumet, Lukas; Eichmann, Thomas O.; Taschler, Ulrike; Zierler, Kathrin A.; Leopold, Christina; Moustafa, Tarek; Radovic, Branislav; Romauch, Matthias; Yan, Cong; Du, Hong; Haemmerle, Guenter; Zechner, Rudolf; Fickert, Peter; Kratky, Dagmar; Zimmermann, Robert; Lass, Achim; Department of Pathology and Laboratory Medicine, IU School of Medicine
    Lysosomal acid lipase (LAL) is essential for the clearance of endocytosed cholesteryl ester and triglyceride-rich chylomicron remnants. Humans and mice with defective or absent LAL activity accumulate large amounts of cholesteryl esters and triglycerides in multiple tissues. Although chylomicrons also contain retinyl esters (REs), a role of LAL in the clearance of endocytosed REs has not been reported. In this study, we found that murine LAL exhibits RE hydrolase activity. Pharmacological inhibition of LAL in the human hepatocyte cell line HepG2, incubated with chylomicrons, led to increased accumulation of REs in endosomal/lysosomal fractions. Furthermore, pharmacological inhibition or genetic ablation of LAL in murine liver largely reduced in vitro acid RE hydrolase activity. Interestingly, LAL-deficient mice exhibited increased RE content in the duodenum and jejunum but decreased RE content in the liver. Furthermore, LAL-deficient mice challenged with RE gavage exhibited largely reduced post-prandial circulating RE content, indicating that LAL is required for efficient nutritional vitamin A availability. In summary, our results indicate that LAL is the major acid RE hydrolase and required for functional retinoid homeostasis.
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    Switch‐1 instability at the active site decouples ATP hydrolysis from force generation in myosin II
    (Wiley, 2021-01) Walker, Benjamin C.; Walczak, Claire E.; Cochran, Jared C.; Medicine, School of Medicine
    Myosin active site elements (i.e., switch-1) bind both ATP and a divalent metal to coordinate ATP hydrolysis. ATP hydrolysis at the active site is linked via allosteric communication to the actin polymer binding site and lever arm movement, thus coupling the free energy of ATP hydrolysis to force generation. How active site motifs are functionally linked to actin binding and the power stroke is still poorly understood. We hypothesize that destabilizing switch-1 movement at the active site will negatively affect the tight coupling of the ATPase catalytic cycle to force production. Using a metal-switch system, we tested the effect of interfering with switch-1 coordination of the divalent metal cofactor on force generation. We found that while ATPase activity increased, motility was inhibited. Our results demonstrate that a single atom change that affects the switch-1 interaction with the divalent metal directly affects actin binding and productive force generation. Even slight modification of the switch-1 divalent metal coordination can decouple ATP hydrolysis from motility. Switch-1 movement is therefore critical for both structural communication with the actin binding site, as well as coupling the energy of ATP hydrolysis to force generation.