Browsing by Author "Jez, Joseph M."

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Molecular basis of the evolution of methylthioalkylmalate synthase and diversity of methionine-derived glucosinolates
(American Society of Plant Biologists, 2019) Kumar, Roshan; Lee, Soon Goo; Augustine, Rehna; Reichelt, Micheal; Vassão, Daniel G.; Palavalli, Manoj H.; Allen, Aron; Gershenzon, Jonathan; Jez, Joseph M.; Bisht, Naveen C.
Methylthioalkylmalate synthase catalyzes the committed step in the side-chain elongation of methionine-derived aliphatic glucosinolates and likely evolved from the isopropylmalate synthases of leucine biosynthesis. The globally cultivated Brassica species possess diverse aliphatic glucosinolates important for plant defense and animal nutrition; however, the molecular basis for the evolution of methylthioalkylmalate synthase and its generation of natural product diversity in Brassica is poorly understood. Here we show that Brassica genomes encode multiple methylthioalkylmalate synthase that have differences in expression profiles and 2-oxo substrate preference that account for diversity of aliphatic glucosinolates across Brassica accessions. The 2.1 Å resolution x-ray crystal structure of B. juncea methylthioalkylmalate synthase identifies key active site residues responsible for controlling specificity for different 2-oxo substrates and the determinants of side-chain length in aliphatic glucosinolates. Overall, these results provide the evolutionary and biochemical foundation for diversification of glucosinolates profiles across globally-cultivated Brassica species, which could be used with ongoing breeding strategies towards manipulation of beneficial glucosinolates compounds for animal health and plant protection.
Two chimeric regulators of G-protein signaling (RGS) proteins differentially modulate soybean heterotrimeric G-protein cycle
(The American Society for Biochemistry and Molecular Biology, 2012) Choudhury, Swarup Roy; Westfall, Corey S.; Laborde, John P.; Bisht, Naveen C.; Jez, Joseph M.; Pandey, Sona
Heterotrimeric G-proteins and the regulator of G-protein signaling (RGS) proteins, which accelerate the inherent GTPase activity of Gα proteins, are common in animals and encoded by large gene families; however, in plants G-protein signaling is thought to be more limited in scope. For example, Arabidopsis thaliana contains one Gα, one Gβ, three Gγ, and one RGS protein. Recent examination of the Glycine max (soybean) genome reveals a larger set of G-protein-related genes and raises the possibility of more intricate G-protein networks than previously observed in plants. Stopped-flow analysis of GTP-binding and GDP/GTP exchange for the four soybean Gα proteins (GmGα1-4) reveals differences in their kinetic properties. The soybean genome encodes two chimeric RGS proteins with an N-terminal seven transmembrane domain and a C-terminal RGS box. Both GmRGS interact with each of the four GmGα and regulate their GTPase activity. The GTPase-accelerating activities of GmRGS1 and -2 differ for each GmGα, suggesting more than one possible rate of the G-protein cycle initiated by each of the Gα proteins. The differential effects of GmRGS1 and GmRGS2 on GmGα1-4 result from a single valine versus alanine difference. The emerging picture suggests complex regulation of the G-protein cycle in soybean and in other plants with expanded G-protein networks.