Origin of diverse phosphorylation patterns in the ERBB system

シグナル伝達による多様な細胞応答の起源 --実験と理論の融合による反応特性の決定. 京都大学プレスリリース. 2022-01-21.Intercellular signals induce various cellular responses, including growth, proliferation, and differentiation, via the dynamic processes of signal transduction pathways. For cell fate decisions, ligand-binding induces the phosphorylation of ERBB receptors, which in turn activate downstream molecules. The ERBB family includes four subtypes, which diverged through two gene duplications from a common ancestor. Differences in the expression patterns of the subtypes have been reported between different organs in the human body. However, how these different expression properties influence the diverse phosphorylation levels of ERBB proteins is not well understood. Here we study the origin of the phosphorylation responses by experimental and mathematical analyses. The experimental measurements clarified that the phosphorylation levels heavily depend on the ERBB expression profiles. We developed a mathematical model consisting of the four subtypes as monomers, homodimers, and heterodimers and estimated the rate constants governing the phosphorylation responses from the experimental data. To understand the origin of the diversity, we analyzed the effects of the expression levels and reaction rates of the ERBB subtypes on the diversity. The difference in phosphorylation rates between ERBB subtypes showed a much greater contribution to the diversity than did the dimerization rates. This result implies that divergent evolution in phosphorylation reactions rather than in dimerization reactions after whole genome duplications was essential for increasing the diversity of the phosphorylation responses

Biotransformation of organic compounds in vivo using larvae of beetles (Allomyrina dichotoma) as biocatalysts

The biotransformation of organic compounds using the larvae of the Japanese rhinoceros beetle (Allomyrina dichotoma) as a biocatalyst is described. When phenyl alkanediones were administered by mouth (p.o) or subcutaneous injection (s.c) to the beetle, asymmetric reduction occurred to yield the corresponding diols in varying optical yields: 1-phenyl-1,2-propandione or 1-phenyl-1,3-butanedione reduced to (1R,2S)- and (1S,2S)-1,2-phenylpropanediols in high optical yields or (1R,3S)- and (1R,3R)-1-phenyl-1,3-butanediols in low to high optical yields, respectively. By administrating 1-phenyl-1-propanone, 1-phenyl-1-butanone or 4-phenyl-2-butanone, redox reactions occurred to give 1-phenyl-1,2-propanediols or 1-phenyl-1,3-butanediols in lower optical yields. The administrations of β-ionone and cinnamyl chloride resulted in regioselective allylic oxidations producing enone and cinnamic acid, respectively. However, when (R)-(-)-carvone was administered, regiospecific dihydroxylation at the isopropenyl group occurred to give (4R,8R)- and (4R,8S)-8,9-dihydroxy-8,9-dihydrocarvone as diastereoisomers. These results appear to demonstrate similar reaction tendency with the case of a microorganism. It is possible that these reactions were due in part to bacteria in the intestine of the larva: however, regio- and stereoselectivities of the reactions were sometimes unique. Thus, it is supposed that these biotransformations were accomplished by the ensemble of the larva׳s own enzymes with several bacteria. The results obtained in this study might show the possibility of using such enzymes derived from insects, including beetle larvae, as a biocatalyst

Single-molecule observation of the ligand-induced population shift of rhodopsin, a g-protein-coupled receptor.

Rhodopsin is a G-protein-coupled receptor, in which retinal chromophore acts as inverse-agonist or agonist depending on its configuration and protonation state. Photostimulation of rhodopsin results in a pH-dependent equilibrium between the active state (Meta-II) and its inactive precursor (Meta-I). Here, we monitored conformational changes of rhodopsin using a fluorescent probe Alexa594 at the cytoplasmic surface, which shows fluorescence increase upon the generation of active state, by single-molecule measurements. The fluorescence intensity of a single photoactivated rhodopsin molecule alternated between two states. Interestingly, such a fluorescence alternation was also observed for ligand-free rhodopsin (opsin), but not for dark-state rhodopsin. In addition, the pH-dependences of Meta-I/Meta-II equilibrium estimated by fluorescence measurements deviated notably from estimates based on absorption spectra, indicating that both Meta-I and Meta-II are mixtures of two conformers. Our observations indicate that rhodopsin molecules intrinsically adopt both active and inactive conformations, and the ligand retinal shifts the conformational equilibrium. These findings provide dynamical insights into the activation mechanisms of G-protein-coupled receptors

Retrieval of a Micra transcatheter pacing system in a heart with a preexisting lead

We report the case of a 74-year-old man with a previously implanted pacemaker lead. He had undergone Medtronic™ Micra Transcatheter Pacing System (TPS, Medtronic plc, MN, USA) implantation because of lead fracture. We implanted a new TPS and retrieved the dislodged one. We used a multiple-loop snare (EN snare®) and an 8.5F steerable sheath (Agilis NXT; St. Jude Medical, St Paul, MN, USA). The TPS was obstructed by the chordae tendineae of the tricuspid valve and the pacemaker lead. We pushed the TPS to the apex site; this enabled us to move the TPS away from the chordae tendineae and pacemaker lead. The TPS body was caught in the inferior vena cava and was successfully retrieved. To our knowledge, this is the first case reporting TPS retrieval in a heart with preexisting lead. Keywords: Dislodgement, Transcatheter pacing system, TPS retrieva

Radiofrequency ablation of ventricular premature contraction originating from a native coronary cusp after transcatheter aortic valve replacement

We describe a case of radiofrequency ablation of ventricular premature contraction (VPC) originating from the left ventricular outflow tract after transcatheter aortic valve replacement. The VPC origin was the native aortic valve annulus between the left and right coronary cusps. Radiofrequency ablation was successfully performed by manipulating the ablation catheter from the gap between the sinotubular junction and implanted valve. Keywords: Radiofrequency ablation, Transcatheter aortic valve replacement, Ventricular premature contraction, Ventricular arrhythmi

Comparative Analysis of Single-Molecule Dynamics of TRPV1 and TRPV4 Channels in Living Cells

TRPV1 and TRPV4, members of the transient receptor potential vanilloid family, are multimodal ion channels activated by various stimuli, including temperature and chemicals. It has been demonstrated that TRPV channels function as tetramers; however, the dynamics of the diffusion, oligomerization, and endocytosis of these channels in living cells are unclear. Here we undertook single-molecule time-lapse imaging of TRPV1 and TRPV4 in HEK 293 cells. Differences were observed between TRPV1 and TRPV4 before and after agonist stimulation. In the resting state, TRPV4 was more likely to form higher-order oligomers within immobile membrane domains than TRPV1. TRPV1 became immobile after capsaicin stimulation, followed by its gradual endocytosis. In contrast, TRPV4 was rapidly internalized upon stimulation with GSK1016790A. The selective loss of immobile higher-order oligomers from the cell surface through endocytosis increased the proportion of the fast-diffusing state for both subtypes. With the increase in the fast state, the association rate constants of TRPV1 and TRPV4 increased, regenerating the higher-order oligomers. Our results provide a possible mechanism for the different rates of endocytosis of TRPV1 and TRPV4 based on the spatial organization of the higher-order structures of the two TRPV channels

Shift in Conformational Equilibrium Induces Constitutive Activity of G-Protein-Coupled Receptor, Rhodopsin

Constitutively active mutants (CAMs) of G-protein-coupled receptors (GPCRs) cause various kinds of diseases. Rhodopsin, a light-absorbing GPCR in animal retinas, has retinal as an endogenous ligand; only very low levels of activation of G-protein can be obtained with the ligand-free opsin. However, the CAM of opsin activates G-protein much more efficiently than the wild type, but the mechanism underlying this remains unclear. The present work revisits the constitutive activity of rhodopsin from the standpoint of conformational dynamics. Single-molecule observation of the M257Y mutant of bovine rhodopsin demonstrated that the switch between active and inactive conformations frequently occurred in M257Y opsin, and frequent generation of the active state results in the population shift toward the active state, which accounts for the constitutive activity of M257Y opsin. Our findings demonstrate that the protein function has a direct connection with the structural dynamics