Anti-CLINT1 polyclonal antibody

Soluble NSF attachment protein receptors (SNAREs) are type II transmembrane proteins that have critical roles in providing the specificity and energy for transport-vesicle fusion and must therefore be correctly partitioned between vesicle and organelle membranes(1-3). Like all other cargo, SNAREs need to be sorted into the forming vesicles by direct interaction with components of the vesicles' coats. Here we characterize the molecular details governing the sorting of a SNARE into clathrin-coated vesicles, namely the direct recognition of the three-helical bundle H-abc domain of the mouse SNARE Vti1b by the human clathrin adaptor epsinR (EPNR, also known as CLINT1). Structures of each domain and of their complex show that this interaction ( dissociation constant 22 mu M) is mediated by surface patches composed of approximately 15 residues each, the topographies of which are dependent on each domain's overall fold. Disruption of the interface with point mutations abolishes the interaction in vitro and causes Vti1b to become relocalized to late endosomes and lysosomes. This new class of highly specific, surface-surface interaction between the clathrin coat component and the cargo is distinct from the widely observed binding of short, linear cargo motifs by the assembly polypeptide (AP) complex and GGA adaptors(4) and is therefore not vulnerable to competition from standard motif-containing cargoes for incorporation into clathrin-coated vesicles. We propose that conceptually similar but mechanistically different interactions will direct the post-Golgi trafficking of many SNAREs.

Angular-type pyranocoumarins (APs) show attractive prospects in anti- hypertension, chemotherapy and anti-HIV treatment. Previous studies revealed extensive hepatic metabolisms of several APs following similar pathways. This study investigated the enzyme kinetics and the main CYP450 isozyme(s) involved in metabolism of (+)-praeruptorin A (dPA), an AP with significant cardio-protective activities, in human liver microsomes (HLMs) using ultra high-performance liquid chromatography coupled with a hybrid quadrupole-linear ion trap mass spectrometry (UHPLC-QT-MS/MS). dPA produced 6 metabolites via hydrolysis (M1-M3), oxidation (M4-M6), and hydrolysis followed by acyl migration (M2 or M3). Oxidation at the C-3' side chain instead of the coumarin ring was consolidated with the aromatic proton signal in NMR spectra. The major metabolite (-)-cis-khellactone (M1) followed biphasic kinetics in HLMs with high affinity (K-m1 0.02 mu M) and intrinsic clearance (CLint1, (in vitro) 1.29 mL/min/mg protein), whereas other metabolites (M2-M6) fitted typical Michaelis-Menten kinetics with lower affinity (K-m 3.85-39.13 mu M). Recombinant human CYP3A4 showed the highest activity toward M1 and M4 formation, while it was CYP2C19 for M2/M3 and M5 and CYP2B6 for M6. Principal component analysis of the metabolite formation profile of dPA also revealed the highest similarity between CYP3A4 and HLMs. Both quercetin (CYP2C8 inhibitor) and ketoconazole (CYP3A4 inhibitor) showed 60-100% inhibition of M1-M4 and M6 formations in HLMs, while M5 formation was mainly inhibited by alpha-naphthoflavone (CYP1A2 inhibitor, 70-80%) and quercetin (90%). Moreover, formations of all metabolites were predominantly inhibited by CYP3A4 antibody (37-68%). These findings shed a light on main involvement of CYP3A4 in human hepatic elimination of APs, indicating potential drug interactions. (c) 2013 Elsevier B.V. All rights reserved.