Enhancement of Edwardsiella piscicida infection, biofilm formation, and motility caused by N-acetylneuraminate lyase

Sialic acid and its catabolism are involved in bacterial pathogenicity. N-acetylneuraminate lyase (NAL), which catalyzes the reversible aldol cleavage of sialic acid to form N-acetyl-D-mannosamine in the first step of sialic acid degradation, has been recently investigated to elucidate whether NAL enhances bacterial virulence; however, the role of NAL in bacterial pathogenicity remains unclear. In the present study, we demonstrated that the existence of two enzymes in Edwardsiella piscicida, referred to as dihydrodipicolinate synthase (DHDPS) and NAL, induced the cleavage/condensation activity toward sialic acids such as N-acetylneuraminic acid, N-glycolylneuraminic acid and 3-deoxy-D-glycero-D-galacto-non-2-ulopyranosonic acid. NAL enhanced cellular infection in vitro and suppressed the survival rate in zebrafish larvae in bath-infection in vivo, whereas DHDPS did not. Furthermore, NAL strongly activated the expression of E. piscicida phenotypes such as biofilm formation and motility, whereas DHDPS did not. Besides, the gene expression level of nanK, nanE, and glmU were up-regulated in the NAL-overexpressing strain, along with an increase in the total amount of N-acetylglucosamine.

Synthesis and structure-activity relationship studies of 2,4-thiazolidinediones and analogous heterocycles as inhibitors of dihydrodipicolinate synthase

Dihydrodipicolinate synthase (DHDPS), responsible for the first committed step of the diaminopimelate pathway for lysine biosynthesis, has become an attractive target for the development of new antibacterial and herbicidal agents. Herein, we report the discovery and exploration of the first inhibitors of E. coli DHDPS which have been identified from screening lead and are not based on substrates from the lysine biosynthesis pathway. Over 50 thiazolidinediones and related analogues have been prepared in order to thoroughly evaluate the structure-activity relationships against this enzyme of significant interest.

Engineering a feedback inhibition-insensitive plant dihydrodipicolinate synthase to increase lysine content in Camelina sativa seeds

Camelina sativa (camelina) is emerging as an alternative oilseed crop due to its short growing cycle, low input requirements, adaptability to less favorable growing environments and a seed oil profile suitable for biofuel and industrial applications. Camelina meal and oil are also registered for use in animal and fish feeds; however, like meals derived from most cereals and oilseeds, it is deficient in certain essential amino acids, such as lysine. In higher plants, the reaction catalyzed by dihydrodipicolinate synthase (DHDPS) is the first committed step in the biosynthesis of lysine and is subject to regulation by lysine through feedback inhibition. Here, we report enhancement of lysine content in C. sativa seed via expression of a feedback inhibition-insensitive form of DHDPS from Corynebacterium glutamicums (CgDHDPS). Two genes encoding C. sativa DHDPS were identified and the endogenous enzyme is partially insensitive to lysine inhibition. Site-directed mutagenesis was used to examine the impact of alterations, alone and in combination, present in lysine-desensitized DHDPS isoforms from Arabidopsis thaliana DHDPS (W53R), Nicotiana tabacum (N80I) and Zea mays (E84K) on C. sativa DHDPS lysine sensitivity. When introduced alone, each of the alterations decreased sensitivity to lysine; however, enzyme specific activity was also affected. There was evidence of molecular or structural interplay between residues within the C. sativa DHDPS allosteric site as coupling of the W53R mutation with the N80V mutation decreased lysine sensitivity of the latter, but not to the level with the W53R mutation alone. Furthermore, the activity and lysine sensitivity of the triple mutant (W53R/N80V/E84T) was similar to the W53R mutation alone or the C. glutamicum DHDPS. The most active and most lysine-insensitive C. sativa DHDPS variant (W53R) was not inhibited by free lysine up to 1 mM, comparable to the C. glutamicums enzyme. Seed lysine content increased 13.6 -22.6% in CgDHDPS transgenic lines and 7.6–13.2% in the mCsDHDPS lines. The high lysine-accumulating lines from this work may be used to produce superior quality animal feed with improved essential amino acid profile.

Asparagine-84, a regulatory allosteric site residue, helps maintain the quaternary structure of Campylobacter jejuni dihydrodipicolinate synthase

Dihydrodipicolinate synthase (DHDPS) from Campylobacter jejuni is a natively homotetrameric enzyme that catalyzes the first unique reaction of (S)-lysine biosynthesis and is feedback-regulated by lysine through binding to an allosteric site. High-resolution structures of the DHDPS-lysine complex have revealed significant insights into the binding events. One key asparagine residue, N84, makes hydrogen bonds with both the carboxyl and the α-amino group of the bound lysine. We generated two mutants, N84A and N84D, to study the effects of these changes on the allosteric site properties. However, under normal assay conditions, N84A displayed notably lower catalytic activity, and N84D showed no activity. Here we show that these mutations disrupt the quaternary structure of DHDPS in a concentration-dependent fashion, as demonstrated by size-exclusion chromatography, multi-angle light scattering, dynamic light scattering, small-angle X-ray scattering (SAXS) and high-resolution protein crystallography.

Dihydrodipicolinate Synthase: Structure, Dynamics, Function, and Evolution

Enzymes are usually comprised of multiple subunits and more often than not they are made up of identical subunits. In this review we examine lysine biosynthesis and focus on the enzyme dihydrodipicolinate synthase in terms of its structure, function and the evolution of its varied number of subunits (quaternary structure). Dihydrodipicolinate synthase is the first committed step in the biosynthesis of lysine, which occurs naturally in plants, bacteria, archaea and fungi, but is not synthesized in mammals. In bacteria, there have been four separate pathways identified from tetrahydrodipicolinate to meso-diaminopimelate, which is the immediate precursor to lysine. Dihydrodipicolinate synthases from many bacterial and plant species have been structurally characterised and the results show considerable variability with respect to their quaternary structure, hinting at their evolution. The oligomeric state of the enzyme plays a key role, both in catalysis and in the allosteric regulation of the enzyme by lysine. While most bacteria and plants have tetrameric enzymes, where the structure of the dimeric building blocks is conserved, the arrangement of the dimers differs. We also review a key development in the field, namely the discovery of a human dihydrodipicolinate synthase-like enzyme, now known as 4-hydroxy-2-oxoglutarate aldolase . This discovery complicates the rationale underpinning drug development against bacterial dihydrodipicolinate synthases, since genetic errors in 4-hydroxy-2-oxoglutarate aldolase cause the disease Primary Hyperoxaluria Type 3 and therefore compounds that are geared towards the inhibition of bacterial dihydrodipicolinate synthase may be toxic to mammalian cells.

Quaternary Structure Analyses of an Essential Oligomeric Enzyme

Here, we review recent studies aimed at defining the importance of quaternary structure to a model oligomeric enzyme, dihydrodipicolinate synthase. This will illustrate the complementary and synergistic outcomes of coupling the techniques of analytical ultracentrifugation with enzyme kinetics, in vitro mutagenesis, macromolecular crystallography, small angle X-ray scattering, and molecular dynamics simulations, to demonstrate the role of subunit self-association in facilitating protein dynamics and enzyme function. This multitechnique approach has yielded new insights into the molecular evolution of protein quaternary structure.

Lysine metabolism in antisense C-hordein barley grains

The grain proteins of barley are deficient in lysine and threonine due to their low concentrations in the major storage protein class, the hordeins, especially in the C-hordein subgroup. Previously produced antisense C-hordein transgenic barley lines have an improved amino acid composition, with increased lysine, methionine and threonine contents. The objective of the study was to investigate the possible changes in the regulation of key enzymes of the aspartate metabolic pathway and the contents of aspartate-derived amino acids in the nontransgenic line (Hordeum vulgare L. cv. Golden Promise) and five antisense C-hordein transgenic barley lines. Considering the amounts of soluble and protein-bound aspartate-derived amino acids together with the analysis of key enzymes of aspartate metabolic pathway, we suggest that the C-hordein suppression did not only alter the metabolism of at least one aspartate-derived amino acid (threonine), but major changes were also detected in the metabolism of lysine and methionine. Modifications in the activities and regulation of aspartate kinase, dihydrodipicolinate synthase and homoserine dehydrogenase were observed in most transgenic lines. Furthermore the activities of lysine α-ketoglutarate reductase and saccharopine dehydrogenase were also altered, although the extent varied among the transgenic lines.