Mitochondrial presequences can induce aggregation of unfolded proteins

AbstractWe have studied the interactions between various synthetic peptides and two model unfolded proteins, reduced α-lactalbumin and reduced and carboxymethylated α-lactalbumin. We found that mitochondrial presequences could induce aggregation of the unfolded α-lactalbumins but not of the native α-lactalbumin. The presequence-induced aggregation of unfolded α-lactalbumin was dependent on electrostatic interactions and on the amphiphilicity of the presequences. Since positive charge and amphiphilicity are necessary for the targeting function of mitochondrial presequences, presequence-induced aggregation may be responsible for the instability of mitochondrial precursor proteins and may need to be inhibited by binding factors in the cytosol

Effects of tooth bleaching on shear bond strength of brackets rebonded with a self-etching adhesive system

The purpose of this study was to ascertain the effects of tooth bleaching on the shear bond strength of orthodontic brackets rebonded with a self-etching adhesive system. A total of 39 premolars were collected and divided into three equal groups: in group 1 bracket bonding was performed without bleaching treatment; Specimens in group 2 were bonded immediately after bleaching; and group 3 teeth were bleached, then immersed in artificial saliva and left for 7 days before bonding. The shear bond strength was measured, with the bonding/debonding procedures repeated once after the first debonding, and the bracket/adhesive failure modes were evaluated by the adhesive remnant index after each debonding. Excepting the mean shear bond strength for group 2 after the first debonding, the overall mean values reached the minimum clinical requirement of 6MPa. The mean values at the first and second debondings were significantly higher in groups 1 and 3 than in group 2. Between groups 1 and 3, significant differences were noted at the first debonding, but not at the second debonding. Group 2 showed significant differences in mean shear bond strength between the first and second debondings. Bond failure at the enamel-adhesive interface occurred more frequently in group 2 than in groups 1 and 3 after the first debonding. The bracket-rebonding procedure can recover the reduced shear bond strength caused by immediate bonding after bleaching to a clinically acceptable level, but not to the prebleaching level

Demonstration of chondroitin sulfates degrading endo-β-glucuronidase activity in rabbit liver

AbstractReduced chondroitin sulfate was incubated with rabbit liver extracts followed by reduction once more with sodium [3H]borohydride, and then passed through a Sephadex G-100 column. Chondroitin sulfate obtained from the incubation medium at pH 4 was only slightly depolymerized and was highly radioactive. Paper Chromatographic analyses showed that glucuronic acid residues became exposed at the reducing terminal of chondroitin sulfate after incubation with the liver extracts. These results suggest that endo-β-glucuronidase activity which degrades chondroitin sulfate is present in the rabbit liver

TIM23-mediated insertion of transmembrane alpha-helices into the mitochondrial inner membrane

While overall hydrophobicity is generally recognized as the main characteristic of transmembrane (TM) alpha-helices, the only membrane system for which there are detailed quantitative data on how different amino acids contribute to the overall efficiency of membrane insertion is the endoplasmic reticulum (ER) of eukaryotic cells. Here, we provide comparable data for TIM23-mediated membrane protein insertion into the inner mitochondrial membrane of yeast cells. We find that hydrophobicity and the location of polar and aromatic residues are strong determinants of membrane insertion. These results parallel what has been found previously for the ER. However, we see striking differences between the effects elicited by charged residues flanking the TM segments when comparing the mitochondrial inner membrane and the ER, pointing to an unanticipated difference between the two insertion systems. Keywords: CoxVa , membrane protein , Mgm1p , mitochondria , TIM2

NMR analyses on the interactions of the yeast Tim50 C-terminal region with the presequence and Tim50 core domain

AbstractThe mitochondrial targeting signal in the presequence of mitochondrial precursor proteins is recognized by Tom20 and subsequently by Tim50 in mitochondria. Yeast Tim50 contains two presequence binding sites in the conserved core domain and in the fungi-specific C-terminal presequence binding domain (PBD). We report the NMR analyses on interactions of a shorter variant of PBD (sPBD), a shorter variant of PBD, with presequences. The presequence is recognized by sPBD in a similar manner to Tom20. sPBD can also bind to the core domain of Tim50 through the presequence binding region, which could promote transfer of the presequence from sPBD to the core domain in Tim50

Two novel proteins in the mitochondrial outer membrane mediate β-barrel protein assembly

Mitochondrial outer and inner membranes contain translocators that achieve protein translocation across and/or insertion into the membranes. Recent evidence has shown that mitochondrial β-barrel protein assembly in the outer membrane requires specific translocator proteins in addition to the components of the general translocator complex in the outer membrane, the TOM40 complex. Here we report two novel mitochondrial outer membrane proteins in yeast, Tom13 and Tom38/Sam35, that mediate assembly of mitochondrial β-barrel proteins, Tom40, and/or porin in the outer membrane. Depletion of Tom13 or Tom38/Sam35 affects assembly pathways of the β-barrel proteins differently, suggesting that they mediate different steps of the complex assembly processes of β-barrel proteins in the outer membrane

Shear bond strength of rebonded brackets after removal of adhesives with Er,Cr:YSGG laser

This study was conducted to examine the bond strength of rebonded orthodontic brackets after adhesive residuals on the surface of the bracket bases were removed by Er,Cr:YSGG lasers. Seventy-six brackets bonded to premolars with a self-etching primer adhesive system were equally divided into four groups after the first debonding with the bracket bases (Group 1) untreated, and treated by (Group 2) Er,Cr:YSGG laser, (Group 3) sandblaster, and (Group 4) Er,Cr:YSGG laser/sandblaster. The treated brackets were rebonded to the new premolars in the same manner as the first-stage experiment. The shear bond strengths were measured, with the bonding/debonding procedures repeated once after the first debonding, and the bracket/adhesive failure modes were evaluated after each debonding. The treated bracket base surfaces were observed under a scanning electron microscopy (SEM). The mean rebond strengths were significantly lower in group 1 than in other groups, and that there were no significant differences between the other groups. The mean initial bond strength was significantly higher than the mean rebond strength in group 1 but there was no significant difference between the two in the other three groups. Failures at the bracket-adhesive interface occurred frequently at second debonding in group 1. Under the SEM, residual adhesive was removed from the bracket bases by Er,Cr:YSGG laser, while adhesive remnant was seen underneath the meshwork of the bracket bases and microroughness appeared on the meshwork after sandblasting. Er,Cr:YSGG laser certainly could serve the purpose of promoting the use of recycled orthodontic brackets