Biomedical subjects

Yoshiko Usami

Publications and source records attributed to Yoshiko Usami.

4 recordsLinked to original sources

PubMed2006

Release of autoinhibition converts ESCRT-III components into potent inhibitors of HIV-1 budding.

The endosomal sorting complex ESCRT-III, which is formed by the structurally related CHMP proteins, is engaged by HIV-1 to promote viral budding. Here we show that progressive truncations into the C-terminal acidic domains of CHMP proteins trigger an increasingly robust anti-HIV budding activity. Together with biochemical evidence for specific intramolecular interactions between the basic and acidic halves of CHMP3 and CHMP4B, these results suggest that the acidic domains are autoinhibitory. The acidic half of CHMP3 also interacts with the endosome-associated ubiquitin isopeptidase AMSH, and the coexpression of AMSH or its CHMP3-binding domain converts wild-type CHMP3 into a potent inhibitor of HIV-1 release. Point mutations in CHMP3 that prevent binding to AMSH abrogate this effect, suggesting that binding to AMSH relieves the autoinhibition of CHMP3. Collectively, our results indicate that CHMP proteins are regulated through an autoinhibitory switch mechanism that allows tight control of ESCRT-III assembly.

Acids↗

PubMed2006

Structural basis for budding by the ESCRT-III factor CHMP3.

The vacuolar protein sorting machinery regulates multivesicular body biogenesis and is selectively recruited by enveloped viruses to support budding. Here we report the crystal structure of the human ESCRT-III protein CHMP3 at 2.8 A resolution. The core structure of CHMP3 folds into a flat helical arrangement that assembles into a lattice, mainly via two different dimerization modes, and unilaterally exposes a highly basic surface. The C terminus, the target for Vps4-induced ESCRT disassembly, extends from the opposite side of the membrane targeting region. Mutations within the basic and dimerization regions hinder bilayer interaction in vivo and reverse the dominant-negative effect of a truncated CHMP3 fusion protein on HIV-1 budding. Thus, the final steps in the budding process may include CHMP protein polymerization and lattice formation on membranes by employing different bilayer-recognizing surfaces, a function shared by all CHMP family members.

Amino Acid Sequence↗

PubMed2004

Pharmacokinetics of lopinavir after administration of Kaletra in healthy Japanese volunteers.

The pharmacokinetic parameters of lopinavir (LPV) were examined by administering Kaletra (LPV+ritonavir) to 8 healthy Japanese volunteers both in the fasting and postprandial conditions. LPV showed a biphasic decline, which was slower in the initial phase and became more rapid in the later phase. The behavior of LPV in the initial phase could be modeled using a one-compartment model with first-order absorption. In the fasting study, calculations based on the pharmacokinetic model revealed that the time to reach the maximum concentration (T(max)), maximum concentration (C(max)), half-life (T(1/2)), lag time, apparent volume of distribution (Vd/F) and oral clearance (Cl/F) were 3.2+/-1.0 h, 6.9+/-1.9 microg/ml, 10.0+/-3.7 h, 0.71+/-0.32 h, 51.0+/-12.4 l and 4.2+/-2.6 l/h, respectively. On the other hand, in the postprandial study, the calculated T(max), C(max), T(1/2), lag time, Vd/F and Cl/F were 5.6+/-2.0 h, 7.6+/-1.8 microg/ml, 16.7+/-7.0 h, 2.35+/-0.78 h, 48.0+/-15.9 l and 2.1+/-0.6 l/h, respectively. The values for the area under the curve for data collected over a 24-h period (AUC(24 h)) in the fasting and postprandial studies were 86.0+/-27.7 and 102.1+/-31.0 microg.h/ml, respectively. The T(1/2) had a tendency to be prolonged after food intake, but there were 2 cases with shortened T(1/2). Food intake prolonged the lag time 3-fold and as a result, the postprandial T(max) was 2 times longer.

Administration, Oral↗

PubMed2003

A simple HPLC method for simultaneous determination of lopinavir, ritonavir and efavirenz.

We developed a simple HPLC method for the simultaneous determination of lopinavir (LPV), ritonavir (RTV) and efavirenz (EFV) to evaluate the efficiency of co-administration of LPV/RTV and EFV in Japanese patients enrolled in a clinical study. The monitoring of LPV plasma concentration is important because co-administration of LPV/RTV with EFV sometimes decreases plasma concentrations of LPV caused by EFV activation of cytochrome P-450 3A. A solution of acetonitrile, methanol and tetramethylammonium perchlorate (TMAP) in dilute aqueous trifluoroacetic acid (TFA) has been used as the mobile phase in a HPLC method to elute LPV and RTV. We found that a solvent ratio of 45 : 5 : 50 (v/v/v) of acetonitrile/methanol/0.02 M TMAP in 0.2% TFA optimized separation of LPV, RTV and EFV. A column temperature of 30 degrees C was necessary for the reproducibility of the analyses. Standard curves were linear in the range 0.060 to 24.06 micro g/ml for LPV, 0.010 to 4.16 micro g/ml for RTV, and 0.047 to 37.44 micro g/ml for EFV. Coefficients of variation (CVs) of LPV, RTV and EFV in intraday and interday assays ranged from 1.5 to 4.0%, 2.5 to 16.8% and 1.0 to 7.7%, respectively. Accuracies ranged from 100 to 110%, 101 to 116% and 99 to 106% for LPV, RTV and EFV, respectively. The extraction recoveries were 77-87, 77-83 and 81-91% for LPV, RTV and EFV, respectively.

Alkynes↗