Comprehensive Analysis of the Chemical and Structural Transformations of Mg-Al-CO3 Layered Double Hydroxides with Different Mg/Al Ratios at Elevated Temperatures.

Mg-Al layered double hydroxides (LDHs) with CO32- interlayer anions are promising CO2 adsorbents. Here, we analyzed the quantitative gas evolution behaviors of Mg-Al LDH particles with different Mg/Al ratios during the multistep chemical/structural transformations at elevated temperatures. The Mg/Al molar ratio strongly affects the behavior: the transformation changes from two apparent steps to three steps depending on the Mg/Al ratio. The transformation occurs in essentially the same way as that observed for large Mg-Al LDH crystals: (1) release of the interlayer water, (2) partial dehydroxylation of the hydroxyl layers followed by coordination of carbonate ions to the metals, and (3) collapse of the layered structure. We provide a molecular/atomic level picture of the structure in each step of the transformation by first-principles density functional theory (DFT) calculation. The structurally optimized model and reexamination of experimental data showed that step (1) results in a large decrease in the interlayer distance of the LDH from ∼7.6 to ∼6.7 Å (a decrease of ∼0.9 Å) and the possible explanation is the waving of the metal hydroxide layers. This study provides a comprehensive understanding of the structural changes of LDHs with various Mg/Al ratios to resolve the various interpretations in the literature.

Synthetic Ubiquinones Specifically Bind to Mitochondrial Voltage-Dependent Anion Channel 1 (VDAC1) in Saccharomyces cerevisiae Mitochondria.

The role of the voltage-dependent anion channel (VDAC) as a metabolic gate of the mitochondrial outer membrane has been firmly established; however, its involvement in the regulation of mitochondrial permeability transition (PT) remains extremely controversial. Although some low-molecular-weight chemicals have been proposed to modulate the regulatory role of VDAC in the induction of PT, direct binding between these chemicals and VDAC has not yet been demonstrated. In the present study, we investigated whether the ubiquinone molecule directly binds to VDAC in Saccharomyces cerevisiae mitochondria through a photoaffinity labeling technique using two photoreactive ubiquinones (PUQ-1 and PUQ-2). The results of the labeling experiments demonstrated that PUQ-1 and PUQ-2 specifically bind to VDAC1 and that the labeled position is located in the C-terminal region Phe221-Lys234, connecting the 15th and 16th ß-strand sheets. Mutations introduced in this region (R224A, Y225A, D228A, and Y225A/D228A) hardly affected the binding affinity of PUQ-1. PUQ-1 and PUQ-2 both significantly suppressed the Ca2+-induced mitochondrial PT (monitored by mitochondrial swelling) at the one digit µM level. Thus, the results of the present study provided, for the first time to our knowledge, direct evidence indicating that the ubiquinone molecule specifically binds to VDAC1 through its quinone-head ring.

Hetero-oligomeric interactions of an ELOVL4 mutant protein: implications in the molecular mechanism of Stargardt-3 macular dystrophy.

PURPOSE: Stargardt disease 3 (STGD3) is a juvenile macular dystrophy caused by mutations in the elongase of very long-chain fatty acids-like 4 (ELOVL4) gene, which encodes an elongase involved in the production of extremely long-chain fatty acids. The STGD3-related mutations cause production of C-terminally truncated proteins (ELOVL4ΔC). STGD3 is transmitted in an autosomal dominant manner. To date, molecular mechanisms of this pathology have been proposed based solely on the interaction between wild-type ELOVL4 and ELOVL4ΔC. However, analyses of Elovl4ΔC knockin mice revealed reduced levels of not only ELOVL4 substrates, but also of fatty acids with a broad spectrum of chain lengths. Therefore, we investigated the molecular mechanisms responsible for ELOVL4ΔC affecting the entire very long-chain fatty acid (VLCFA) elongation pathway. METHODS: The ELOVL4ΔC protein was expressed in HEK 293T cells, and its effect on elongase activities toward several acyl-CoAs were examined. We also investigated the homo- and hetero-oligomerization of ELOVL4ΔC with other elongases (ELOVL1-7) or with other enzymes involved in VLCFA elongation using coimmunoprecipitation experiments. RESULTS: We found that ELOVL4ΔC forms a homo-oligomer more strongly than wild-type ELOVL4. ELOVL4ΔC also interacts strongly with other elongases, although similar interactions for wild-type ELOVL4 were observed as only weak. In addition, ELOVL4ΔC is able to form an elongase complex by interacting with other components of the VLCFA elongation machinery, similar to wild-type ELOVL4. CONCLUSIONS: We propose that not only the ELOVL4-ELOVL4ΔC homo-oligomeric interaction, but also several hetero-oligomeric interactions, may contribute to the pathology of STGD3.

Characterization of HACD1 K64Q mutant found in arrhythmogenic right ventricular dysplasia patients.

Arrhythmogenic right ventricular dysplasia (ARVD) is an autosomal dominant heart disease. A K64Q mutation was found in ARVD-affected individuals in the HACD1 gene, which encodes an enzyme involved in very long-chain fatty acid (VLCFA) elongation, although any relationship between mutation and pathology remained unclear. Here, we demonstrate that HACD1 (K64Q) exhibits normal enzyme activity, intracellular localization and interaction with other VLCFA enzymes, with no dominant negative effect on VLCFA elongation. Thus, it appears unlikely that this mutation is ARVD-causative. Moreover, through these analyses we found that HACD1 interacts with KAR and TER, the reductase enzymes involved in the second and fourth VLCFA elongation cycle, respectively. This finding indicates that the enzymes responsible for the VLCFA elongation cycle form an elongase complex.