Functional diversification within the heme-binding split-barrel family.

Due to neofunctionalization, a single fold can be identified in multiple proteins that have distinct molecular functions. Depending on the time that has passed since gene duplication and the number of mutations, the sequence similarity between functionally divergent proteins can be relatively high, eroding the value of sequence similarity as the sole tool for accurately annotating the function of uncharacterized homologs. Here, we combine bioinformatic approaches with targeted experimentation to reveal a large multi-functional family of putative enzymatic and non-enzymatic proteins involved in heme metabolism. This family (homolog of HugZ (HOZ)) is embedded in the "FMN-binding split barrel" superfamily and contains separate groups of proteins from prokaryotes, plants, and algae, which bind heme and either catalyze its degradation or function as non-enzymatic heme sensors. In prokaryotes these proteins are often involved in iron assimilation, whereas several plant and algal homologs are predicted to degrade heme in the plastid or regulate heme biosynthesis. In the plant Arabidopsis thaliana, which contains two HOZ subfamilies that can degrade heme in vitro (HOZ1 and HOZ2), disruption of AtHOZ1 (AT3G03890) or AtHOZ2A (AT1G51560) causes developmental delays, pointing to important biological roles in the plastid. In the tree Populus trichocarpa, a recent duplication event of a HOZ1 ancestor has resulted in localization of a paralog to the cytosol. Structural characterization of this cytosolic paralog and comparison to published homologous structures suggests conservation of heme-binding sites. This study unifies our understanding of the sequence-structure-function relationships within this multi-lineage family of heme-binding proteins and presents new molecular players in plant and bacterial heme metabolism.

Asymmetric catalytic aza-Morita-Baylis-Hillman reaction for the synthesis of 3-substituted-3-aminooxindoles with chiral quaternary carbon centers.

The asymmetric catalytic aza-Morita-Baylis-Hillman (aza-MBH) reaction of isatin-derived ketimines with MVK has been established by using chiral amino and phosphino catalysts. The reaction resulted in biomedically important 3-substituted 3-amino-2-oxindoles in good yields (>80% for most cases) and with excellent enantioselectivity (90-99% ee). Twenty-eight cases assembled with chiral quaternary stereogenic centers have been examined under convenient systems.

Two related families of metal transferases, ZNG1 and ZNG2, are involved in acclimation to poor Zn nutrition in Arabidopsis.

Metal homeostasis has evolved to tightly modulate the availability of metals within the cell, avoiding cytotoxic interactions due to excess and protein inactivity due to deficiency. Even in the presence of homeostatic processes, however, low bioavailability of these essential metal nutrients in soils can negatively impact crop health and yield. While research has largely focused on how plants assimilate metals, acclimation to metal-limited environments requires a suite of strategies that are not necessarily involved in metal transport across membranes. The identification of these mechanisms provides a new opportunity to improve metal-use efficiency and develop plant foodstuffs with increased concentrations of bioavailable metal nutrients. Here, we investigate the function of two distinct subfamilies of the nucleotide-dependent metallochaperones (NMCs), named ZNG1 and ZNG2, that are found in plants, using Arabidopsis thaliana as a reference organism. AtZNG1 (AT1G26520) is an ortholog of human and fungal ZNG1, and like its previously characterized eukaryotic relatives, localizes to the cytosol and physically interacts with methionine aminopeptidase type I (AtMAP1A). Analysis of AtZNG1, AtMAP1A, AtMAP2A, and AtMAP2B transgenic mutants are consistent with the role of Arabidopsis ZNG1 as a Zn transferase for AtMAP1A, as previously described in yeast and zebrafish. Structural modeling reveals a flexible cysteine-rich loop that we hypothesize enables direct transfer of Zn from AtZNG1 to AtMAP1A during GTP hydrolysis. Based on proteomics and transcriptomics, loss of this ancient and conserved mechanism has pleiotropic consequences impacting the expression of hundreds of genes, including those involved in photosynthesis and vesicle transport. Members of the plant-specific family of NMCs, ZNG2A1 (AT1G80480) and ZNG2A2 (AT1G15730), are also required during Zn deficiency, but their target protein(s) remain to be discovered. RNA-seq analyses reveal wide-ranging impacts across the cell when the genes encoding these plastid-localized NMCs are disrupted.

Drosophila Miro is required for both anterograde and retrograde axonal mitochondrial transport.

Microtubule-based transport of mitochondria into dendrites and axons is vital for sustaining neuronal function. Transport along microtubule tracks proceeds in a series of plus and minus end-directed movements that are facilitated by kinesin and dynein motors. How the opposing movements are controlled to achieve effective transport over large distances remains unclear. Previous studies showed that the conserved mitochondrial GTPase Miro is required for mitochondrial transport into axons and dendrites and serves as a Ca(2+) sensor that controls mitochondrial mobility. To directly examine Miro's significance for kinesin- and/or dynein-mediated mitochondrial motility, we live-imaged movements of GFP-tagged mitochondria in larval Drosophila motor axons upon genetic manipulations of Miro. Loss of Drosophila Miro (dMiro) reduced the effectiveness of both anterograde and retrograde mitochondrial transport by selectively impairing kinesin- or dynein-mediated movements, depending on the direction of net transport. Net anterogradely transported mitochondria exhibited reduced kinesin- but normal dynein-mediated movements. Net retrogradely transported mitochondria exhibited much shorter dynein-mediated movements, whereas kinesin-mediated movements were minimally affected. In both cases, the duration of short stationary phases increased proportionally. Overexpression (OE) of dMiro also impaired the effectiveness of mitochondrial transport. Finally, loss and OE of dMiro altered the length of mitochondria in axons through a mechanistically separate pathway. We suggest that dMiro promotes effective antero- and retrograde mitochondrial transport by extending the processivity of kinesin and dynein motors according to a mitochondrion's programmed direction of transport.

The GTPase dMiro is required for axonal transport of mitochondria to Drosophila synapses.

We have identified EMS-induced mutations in Drosophila Miro (dMiro), an atypical mitochondrial GTPase that is orthologous to human Miro (hMiro). Mutant dmiro animals exhibit defects in locomotion and die prematurely. Mitochondria in dmiro mutant muscles and neurons are abnormally distributed. Instead of being transported into axons and dendrites, mitochondria accumulate in parallel rows in neuronal somata. Mutant neuromuscular junctions (NMJs) lack presynaptic mitochondria, but neurotransmitter release and acute Ca2+ buffering is only impaired during prolonged stimulation. Neuronal, but not muscular, expression of dMiro in dmiro mutants restored viability, transport of mitochondria to NMJs, the structure of synaptic boutons, the organization of presynaptic microtubules, and the size of postsynaptic muscles. In addition, gain of dMiro function causes an abnormal accumulation of mitochondria in distal synaptic boutons of NMJs. Together, our findings suggest that dMiro is required for controlling anterograde transport of mitochondria and their proper distribution within nerve terminals.

Phosphine-catalyzed asymmetric [4+1] annulation of activated α,ß-unsaturated ketones with Morita-Baylis-Hillman carbonates: enantioselective synthesis of spirooxindoles containing two adjacent quaternary stereocenters.

The asymmetric [4+1] annulation of activated α,ß-unsaturated ketones with MBH carbonates catalyzed by bifunctional thiourea-phosphine catalysts derived from an axially chiral binaphthyl scaffold has been developed, giving spirooxindoles with two adjacent quaternary stereocenters in good yields with high enantioselectivities and moderate diastereoselectivities under mild conditions.