Expression Elements Derived From Plant Sequences Provide Effective Gene Expression Regulation and New Opportunities for Plant Biotechnology Traits.

Plant biotechnology traits provide a means to increase crop yields, manage weeds and pests, and sustainably contribute to addressing the needs of a growing population. One of the key challenges in developing new traits for plant biotechnology is the availability of expression elements for efficacious and predictable transgene regulation. Recent advances in genomics, transcriptomics, and computational tools have enabled the generation of new expression elements in a variety of model organisms. In this study, new expression element sequences were computationally generated for use in crops, starting from native Arabidopsis and maize sequences. These elements include promoters, 5' untranslated regions (5' UTRs), introns, and 3' UTRs. The expression elements were demonstrated to drive effective transgene expression in stably transformed soybean plants across multiple tissues types and developmental stages. The expressed transcripts were characterized to demonstrate the molecular function of these expression elements. The data show that the promoters precisely initiate transcripts, the introns are effectively spliced, and the 3' UTRs enable predictable processing of transcript 3' ends. Overall, our results indicate that these new expression elements can recapitulate key functional properties of natural sequences and provide opportunities for optimizing the expression of genes in future plant biotechnology traits.

Distinct Roles for Intracellular and Extracellular Lipids in Hepatitis C Virus Infection.

Hepatitis C is a chronic liver disease that contributes to progressive metabolic dysfunction. Infection of hepatocytes by hepatitis C virus (HCV) results in reprogramming of hepatic and serum lipids. However, the specific contribution of these distinct pools of lipids to HCV infection remains ill defined. In this study, we investigated the role of hepatic lipogenesis in HCV infection by targeting the rate-limiting step in this pathway, which is catalyzed by the acetyl-CoA carboxylase (ACC) enzymes. Using two structurally unrelated ACC inhibitors, we determined that blockade of lipogenesis resulted in reduced viral replication, assembly, and release. Supplementing exogenous lipids to cells treated with ACC inhibitors rescued HCV assembly with no effect on viral replication and release. Intriguingly, loss of viral RNA was not recapitulated at the protein level and addition of 2-bromopalmitate, a competitive inhibitor of protein palmitoylation, mirrored the effects of ACC inhibitors on reduced viral RNA without a concurrent loss in protein expression. These correlative results suggest that newly synthesized lipids may have a role in protein palmitoylation during HCV infection.

Atypical antipsychotics rapidly and inappropriately switch peripheral fuel utilization to lipids, impairing metabolic flexibility in rodents.

Patients taking atypical antipsychotics are frequented by serious metabolic (eg, hyperglycemia, obesity, and diabetes) and cardiac effects. Surprisingly, chronic treatment also appears to lower free fatty acids (FFAs). This finding is paradoxical because insulin resistance is typically associated with elevated not lower FFAs. How atypical antipsychotics bring about these converse changes in plasma glucose and FFAs is unknown. Chronic treatment with olanzapine, a prototypical, side effect prone atypical antipsychotic, lowered FFA in Sprague-Dawley rats. Olanzapine also lowered plasma FFA acutely, concomitantly impairing in vivo lipolysis and robustly elevating whole-body lipid oxidation. Increased lipid oxidation was evident from accelerated losses of triglycerides after food deprivation or lipid challenge, elevated FFA uptake into most peripheral tissues (∼2-fold) except heart, rises in long-chain 3-hydroxylated acyl-carnitines observed in diabetes, and rapid suppression of the respiratory exchange ratio (RER) during the dark cycle. Normal rises in RER following refeeding, a sign of metabolic flexibility, were severely blunted by olanzapine. Increased lipid oxidation in muscle could be explained by ∼50% lower concentrations of the negative cytoplasmic regulator of carnitine palmitoyltransferase I, malonyl-CoA. This was associated with loss of anapleurotic metabolites and citric acid cycle precursors of malonyl-CoA synthesis rather than adenosine monophosphate-activated kinase activation or direct ACC1/2 inhibition. The ability of antipsychotics to lower dark cycle RER in mice corresponded to their propensities to cause metabolic side effects. Our studies indicate that lipocentric mechanisms or altered intermediary metabolism could underlie the FFA lowering and hyperglycemia (Randle cycle) as well as some of the other side effects of atypical antipsychotics, thereby suggesting strategies for alleviating them.

A mechanism for the potent inhibition of eukaryotic acetyl-coenzyme A carboxylase by soraphen A, a macrocyclic polyketide natural product.

Acetyl-coenzyme A carboxylases (ACCs) have crucial roles in fatty acid metabolism. Soraphen A, a macrocyclic polyketide natural product, is a nanomolar inhibitor against the biotin carboxylase (BC) domain of human, yeast, and other eukaryotic ACCs. Here we report the crystal structures of the yeast BC domain, alone and in complex with soraphen A. Soraphen has extensive interactions with an allosteric site, about 25 A from the active site. The specificity of soraphen is explained by large structural differences between the eukaryotic and prokaryotic BC in its binding site, confirmed by our studies on the effects of single-site mutations in this binding site. Unexpectedly, our structures suggest that soraphen may bind in the BC dimer interface and inhibit the BC activity by disrupting the oligomerization of this domain. Observations from native gel electrophoresis confirm this structural insight. The structural information provides a foundation for structure-based design of new inhibitors against these enzymes.

Expression and characterization of recombinant fungal acetyl-CoA carboxylase and isolation of a soraphen-binding domain.

Acetyl-CoA carboxylase (ACC) catalyses the first step in fatty-acid biosynthesis. Owing to its role in primary metabolism, ACC has been exploited as a commercial herbicide target and identified as a chemically validated fungicide target. In animals, ACC is also a key regulator of fat metabolism. This function has made ACC a prime target for the development of anti-obesity and anti-Type II diabetes therapeutics. Despite its economic importance, there is a lack of published information on recombinant expression of ACC. We report here the expression of enzymically active fungal (Ustilago maydis ) ACC in Escherichia coli. The recombinant enzyme exhibited Km values of 0.14+/-0.013 mM and 0.19+/-0.041 mM for acetyl-CoA and ATP respectively, which are comparable with those reported for the endogenous enzyme. The polyketide natural product soraphen is a potent inhibitor of the BC (biotin carboxylase) domain of endogenous fungal ACC. Similarly, recombinant ACC activity was inhibited by soraphen with a K(i) of 2.1+/-0.9 nM. A truncated BC domain that included amino acids 2-560 of the full-length protein was also expressed in E. coli. The isolated BC domain was expressed to higher levels, and was more stable than full-length ACC. Although incapable of enzymic turnover, the BC domain exhibited high-affinity soraphen binding (Kd 1.1+/-0.3 nM), demonstrating a native conformation. Additional BC domains from the phytopathogenic fungi Magnaporthe grisea and Phytophthora infestans were also cloned and expressed, and were shown to exhibit high-affinity soraphen binding. Together, these reagents will be useful for structural studies and assay development.