l-Malate (-2) Protonation State is Required for Efficient Decarboxylation to l-Lactate by the Malolactic Enzyme of Oenococcus oeni

Malolactic fermentation (MLF) is responsible for the decarboxylation of l-malic into lactic acid in most red wines and some white wines. It reduces the acidity of wine, improves flavor complexity and microbiological stability. Despite its industrial interest, the MLF mechanism is not fully understood. The objective of this study was to provide new insights into the role of pH on the binding of malic acid to the malolactic enzyme (MLE) of Oenococcus oeni. To this end, sequence similarity networks and phylogenetic analysis were used to generate an MLE homology model, which was further refined by molecular dynamics simulations. The resulting model, together with quantum polarized ligand docking (QPLD), was used to describe the MLE binding pocket and pose of l-malic acid (MAL) and its l-malate (−1) and (−2) protonation states (MAL⁻ and MAL²⁻, respectively). MAL²⁻ has the lowest ∆G_binding, followed by MAL⁻ and MAL, with values of −23.8, −19.6, and −14.6 kJ/mol, respectively, consistent with those obtained by isothermal calorimetry thermodynamic (ITC) assays. Furthermore, molecular dynamics and MM/GBSA results suggest that only MAL²⁻ displays an extended open conformation at the binding pocket, satisfying the geometrical requirements for Mn²⁺ coordination, a critical component of MLE activity. These results are consistent with the intracellular pH conditions of O. oeni cells—ranging from pH 5.8 to 6.1—where the enzymatic decarboxylation of malate occurs.

Isolation of WDR and bHLH genes related to flavonoid synthesis in grapevine (Vitis vinifera L.)

Anthocyanins and tannins are two of the most abundant flavonoids found in grapevine, and their synthesis is derived from the phenylpropanoid pathway. As described for model species such as Arabidopsis thaliana, maize and petunia, the end-point branches of this pathway are tightly regulated by the combinatorial interaction of three families of regulatory factors; MYB, bHLH (also known as MYC) and WDR proteins. Among these, only MYB genes have been previously identified in grapes. Here, we report the isolation of the first members from the WDR and bHLH families found in Vitis vinifera, named WDR1, WDR2 and MYCA1. WDR1 contributed positively to the accumulation of anthocyanins when it was overexpressed in A. thaliana, although it was not possible to determine the function of WDR2 by ectopic expression. The sub-cellular localizations of WDR1 and MYCA1 were observed by means of GFP-fusion proteins, indicating both cytoplasm and nuclear localization, in contrast to the localization of a MYB factor exclusively in the nucleus. The expression patterns of these genes were quantified in coloured reproductive organs throughout development, and correlated with anthocyanin accumulation and the expression profiles of the flavonoid-related MYBA1-2, UFGT, and ANR genes. In vitro grapevine plantlets grown under high salt concentrations showed a cultivar-dependent response for anthocyanin accumulation, which correlated with the expression of MYBA1-2, MYCA1 and WDR1 genes. These results suggest that MYCA1 may regulate ANR and UFGT and that this last control is easier to distinguish whenever MYBA genes are absent or in low abundance. Future studies should address the specific interactions of these proteins and their quantitative contribution to flavonoid synthesis in grape berries.

Isolation of WDR and bHLH genes related to flavonoid synthesis in grapevine (Vitis vinifera L.)

Anthocyanins and tannins are two of the most abundant flavonoids found in grapevine, and their synthesis is derived from the phenylpropanoid pathway. As described for model species such as Arabidopsis thaliana, maize and petunia, the end-point branches of this pathway are tightly regulated by the combinatorial interaction of three families of regulatory factors; MYB, bHLH (also known as MYC) and WDR proteins. Among these, only MYB genes have been previously identified in grapes. Here, we report the isolation of the first members from the WDR and bHLH families found in Vitis vinifera, named WDR1, WDR2 and MYCA1. WDR1 contributed positively to the accumulation of anthocyanins when it was overexpressed in A. thaliana, although it was not possible to determine the function of WDR2 by ectopic expression. The sub-cellular localizations of WDR1 and MYCA1 were observed by means of GFP-fusion proteins, indicating both cytoplasm and nuclear localization, in contrast to the localization of a MYB factor exclusively in the nucleus. The expression patterns of these genes were quantified in coloured reproductive organs throughout development, and correlated with anthocyanin accumulation and the expression profiles of the flavonoid-related MYBA1-2, UFGT, and ANR genes. In vitro grapevine plantlets grown under high salt concentrations showed a cultivar-dependent response for anthocyanin accumulation, which correlated with the expression of MYBA1-2, MYCA1 and WDR1 genes. These results suggest that MYCA1 may regulate ANR and UFGT and that this last control is easier to distinguish whenever MYBA genes are absent or in low abundance. Future studies should address the specific interactions of these proteins and their quantitative contribution to flavonoid synthesis in grape berries.

Skeletal muscle cells express the profibrotic cytokine connective tissue growth factor (CTGF/CCN2), which induces their dedifferentiation

Fibrotic disorders are typified by excessive connective tissue and extracellular matrix (ECM) deposition that precludes normal healing processes of different tissues. Connective tissue growth factor (CTGF) seems to be involved in the fibrotic response. Several muscular dystrophies are characterized by a progressive weakness and wasting of the musculature, and by extensive fibrosis. However, the exact role of CTGF in skeletal muscle is unknown. Here we show that myoblasts and myotubes are able to synthesize CTGF in response to transforming growth factor type-beta (TGF-beta) and lysophosphatidic acid (LPA). CTGF induced several ECM constituents such as fibronectin, collagen type I and alpha4, 5, 6, and beta1 integrin subunits in myoblasts and myotubes. CTGF had an important inhibitory effect on muscle differentiation evaluated by the decrease in the nuclear translocation of the early muscle regulatory factor myogenin and myosin. Remarkable, CTGF treatment of myoblasts induced their dedifferentiation, characterized by down regulating MyoD and desmin, two markers of committed myoblasts, together with a strong reorganization of cytoskeletal filaments. These results provide novel evidence for the underlying mechanisms and participation of skeletal muscle cells in the synthesis and role of CTGF inducing fibrosis, inhibiting myogenesis and dedifferentiating myoblasts.