Tomohiko Toyoda

Ribosome recycling factor (RRF), in concert with elongation factor EF-G, is required for disassembly of the posttermination complex of the ribosome after release of polypeptides. The crystal structure of Thermus thermophilus RRF was determined at 2.6 A resolution. It is a tRNA-like L-shaped molecule consisting of two domains: a long three-helix bundle (domain 1) and a three-layer beta/alpha/beta sandwich (domain 2). Although the individual domain structures are similar to those of Thermotoga maritima RRF (Selmer et al., Science, 1999, 286:2349-2352), the interdomain angle differs by 33 degrees in two molecules, suggesting that the hinge between two domains is potentially flexible and responsive to different conditions of crystal packing. The hinge connects hydrophobic junctions of domains 1 and 2. The structure-based genetic analysis revealed the strong correlation between the hinge flexibility and the in vivo function of RRF. First, altering the hinge flexibility by making alanine or serine substitutions for large-size residues conserved at the hinge loop and nearby in domain 1 frequently gave rise to gain of function except a Pro residue conserved at the hinge loop. Second, the hinge defect resulting from a too relaxed hinge structure can be compensated for by secondary alterations in domain 1 that seem to increase the hydrophobic contact between domain 1 and the hinge loop. These results show that the hinge flexibility is vital for the function of RRF and that the steric interaction between the hinge loop and domains 1 and 2 restricts the interdomain angle and/or the hinge flexibility. These results indicate that RRF possesses an architectural difference from tRNA regardless of a resemblance to tRNA shape: RRF has a "gooseneck" elbow, whereas the tRNA elbow is rigid, and the direction of flex of RRF and tRNA is at a nearly right angle to each other. Moreover, surface electrostatic potentials of the two RRF proteins are dissimilar and do not mimic the surface potential of tRNA or EF-G. These properties will add a new insight into RRF, suggesting that RRF is more than a simple tRNA mimic.

BACKGROUND: Fontan-associated liver disease (FALD) is an important late complication involving liver dysfunction, such as liver cirrhosis (LC) and hepatocellular carcinoma (HCC), in patients undergoing the Fontan procedure. However, the prevalence, clinical manifestation, and methods of diagnosis of FALD are still not well established. METHODS AND RESULTS: This study comprised 2 nationwide surveys in Japan. First, the prevalence of LC and/or HCC in patients undergoing the Fontan procedure was determined. Second, clinical manifestations in patients with LC and/or HCC were analyzed, along with data from blood tests, echocardiography, and right heart catheterization. In the 1st survey, of the 2,700 patients who underwent the Fontan procedure, 31 were diagnosed with LC and/or HCC (1.15%), and 5 died due to liver diseases (mortality: 0.19%). In the 2nd survey, data were collected from 17 patients (12 with LC, 2 with HCC, and 3 with LC+HCC. Of these 17 patients, 5 died (mortality: 29.4%). The mean age at diagnosis of LC and HCC was 23 and 31 years, respectively. Computed tomography followed by ultrasound was most frequently used for diagnosis. Blood tests revealed low platelet counts, increased hemoglobin, aspartate aminotransferase, γ-guanosine triphosphate, and total bilirubin levels, and an elevated international normalized ratio of prothrombin time. CONCLUSIONS: LC and/or HCC in patients undergoing the Fontan procedure were not rare late complications and were associated with high mortality rates.