Aspartic acid

Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the protonated –NH form under physiological conditions, while its α-carboxylic acid group is deprotonated −COO− under physiological conditions. Aspartic acid has an acidic side chain (CH2COOH) which reacts with other amino acids, enzymes and proteins in the body. Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO−. It is a non-essential amino acid in humans, meaning the body can synthesize it as needed. It is encoded by the codons GAU and GAC. D-Aspartate is one of two D-amino acids commonly found in mammals.[3] In proteins aspartate sidechains are often hydrogen bonded to form asx turns or asx motifs, which frequently occur at the N-termin

Catalytic amino acid production from biomass-derived intermediates

Paul Joseph Dyson, Yu Han, Yefeng Wang, Ning Yan, Shunlin Zhang

Amino acids are the building blocks for protein biosynthesis and find use in myriad industrial applications including in food for humans, in animal feed, and as precursors for bio-based plastics, among others. However, the development of efficient chemical methods to convert abundant and renewable feedstocks into amino acids has been largely unsuccessful to date. To that end, here we report a heterogeneous catalyst that directly transforms lignocellulosic biomass-derived a-hydroxyl acids into a-amino acids, including alanine, leucine, valine, aspartic acid, and phenylalanine in high yields. The reaction follows a dehydrogenation-reductive amination pathway, with dehydrogenation as the rate-determining step. Ruthenium nano-particles supported on carbon nanotubes (Ru/CNT) exhibit exceptional efficiency compared with catalysts based on other metals, due to the unique, reversible enhancement effect of NH3 on Ru in dehydrogenation. Based on the catalytic system, a two-step chemical process was designed to convert glucose into alanine in 43% yield, comparable with the well-established microbial cultivation process, and therefore, the present strategy enables a route for the production of amino acids from renewable feedstocks. Moreover, a conceptual process design employing membrane distillation to facilitate product purification is proposed and validated. Overall, this study offers a rapid and potentially more efficient chemical method to produce amino acids from woody biomass components.

National Academy of Sciences2018

How Vibrio cholerae adapts to the environment: from cell shape transitions to antagonistic behavior

Leonardo Filipe Lemos Rocha

The bacterium Vibrio cholerae is the causative agent of the diarrheal disease cholera, which affects millions of people every year. Apart from being a human pathogen, V. cholerae is also a common member of aquatic habitats. Whilst the mechanism that allow it to transit from an environmental to a pathogenic lifestyle is still understudied, it is well established that virulence induction is linked to the bacterium's ability to sense its surroundings. Therefore, this thesis aimed to shed new light on the general sensing capacity of V. cholerae and its adaptation to the surrounding environment. Specifically, we explored the functions of the virulence-associated regulatory two-component system VarS/VarA, which was shown to regulate the major virulence factors of V. cholerae. In this thesis, we identified a new function of this regulatory system in modulating the pathogen's cellular shape. Precisely, we demonstrated that a strain lacking the response regulator VarA loses its normal curve-shaped morphology and transits to spherical shape during stationary phase of growth. This rounding phenotype was not observed on cells lacking the sensor histidine kinase VarS, which suggests the existence of additional VarA activators. Through analysis of the cells's peptidoglycan (PG), we found that the cause of the atypical shape was due to high abundance of dipeptides and reduced peptide cross-links. This abnormal PG composition and consequent cell rounding could be abrogated through cell wall recycling of wild type-derived PG subunits. Through a transposon mutagenesis screen, we identified the carbon storage regulator A (CsrA) as a key player in this phenotype. We showed that varA-deficient cells have an increased activity of CsrA, which led to an overproduction of the aspartate ammonia lyase enzyme (AspA). Our results indicate that AspA overproduction likely reduced the pool of aspartate in varA-deficient cells, which subsequently impaired the biosynthesis of the cell wall precursor meso-diaminopimelic acid. Ultimately, this compromised production of PG precursors resulted in the altered PG composition and consequent cell rounding. Furthermore, and consistent with findings in Enterobacteriaceae, our results also suggest that the VarA-CsrA regulatory circuit modulates chemotaxis and motility in V. cholerae. Finally, in two different collaborative studies, we also addressed how V. cholerae might interact with other bacteria in the environment taking bacterial antagonism strategies into consideration. Firstly, we showed that a subset of human gut microbiota isolates is able to withstand type VI secretion system (T6SS)-mediated attacks by V. cholerae in an immunity protein-independent manner. Moreover, our preliminary data indicates a superior T6SS-mediated killing potential from a specific environmental strain of V. cholerae compared to a particular toxigenic strain. Secondly, we demonstrated that the environmental V. cholerae strain SA7G harbors a specific plasmid, pSA7G1, that confers a competitive advantage over neighboring bacteria likely through type IV secretion system-mediated killing. Collectively, the findings of this thesis contribute to better understanding how V. cholerae adapts to the environment, namely with specific sensing-response mechanisms such as the VarA-CsrA signaling pathway.

EPFL2022

How Vibrio cholerae adapts to the environment: from cell shape transitions to antagonistic behavior

Leonardo Filipe Lemos Rocha

EPFL2022

Study if biotin replacement by aspartic acid and oleic acid for the expression of recombinant avidin in Picha pastoris in a chemically defined medium

Catalytic amino acid production from biomass-derived intermediates

How Vibrio cholerae adapts to the environment: from cell shape transitions to antagonistic behavior

How Vibrio cholerae adapts to the environment: from cell shape transitions to antagonistic behavior

Study if biotin replacement by aspartic acid and oleic acid for the expression of recombinant avidin in Picha pastoris in a chemically defined medium

Catalytic amino acid production from biomass-derived intermediates