A series of novel morpholines linked coumarin–triazole hybrids (6a–6v) has been synthesized and evaluated for their anti‐proliferative potential on a panel of five human cancer cell lines, namely bone (MG‐63), lung (A549), breast (MDA‐MB‐231), colon (HCT‐15) and liver (HepG2), using MTT assay. Among all, the compound 6n {7‐((1‐(2,4‐dichlorobenzyl)‐1H‐1,2,3‐triazol‐4‐yl) methoxy)‐4‐((2,6‐dimethylmorpholino) methyl)‐2H‐chromen‐2‐one} showed significant growth inhibition against MG‐63 cells with an IC50 value of 0.80 ± 0.22 μM. Further, induction of apoptosis by 6n of MG‐63 cells confirmed as a result of morphological changes, the sub‐G1 phase arrest, increased percentage of apoptotic cells, and decrease in mitochondrial membrane potential and increase in reactive oxygen species levels. The in vitro Gal‐1 expression in cell culture supernatant of MG‐63 cells treated with compound 6n showed dose‐dependent reduction. The binding constant (Ka) of 6n with Gal‐1 was calculated from the intercept value which was observed as 3.0 × 105 M−1 by fluorescence spectroscopy. Surface plasmon resonance showed that 6n binds to Gal‐1 with binding constant (Ka) of 1.29E+04 1/Ms and equilibrium constant KD value of 7.54E−07 M, respectively. Molecular docking studies revealed the binding interactions of 6n with Gal‐1.

The nickel-pincer nucleotide (NPN) coenzyme, a substituted pyridinium mononucleotide that tri-coordinates nickel, was first identified covalently attached to a lysine residue in the LarA protein of lactate racemase. Starting from nicotinic acid adenine dinucleotide, LarB carboxylates C5 of the pyridinium ring and hydrolyzes the phosphoanhydride, LarE converts the C3 and C5 carboxylates to thiocarboxylates, and LarC incorporates nickel to form a C–Ni and two S–Ni bonds, during the biosynthesis of this cofactor. LarB uses a novel carboxylation mechanism involving the transient formation of a cysteinyl-pyridinium adduct. Depending on the source of the enzyme, LarEs either catalyze a sacrificial sulfur transfer from a cysteinyl side chain resulting in the formation of dehydroalanine or they utilize a [4Fe–4S] cluster bound by three cysteine residues to accept and transfer a non-core sulfide atom. LarC is a CTP-dependent enzyme that cytidinylylates its substrate, adds nickel, then hydrolyzes the product to release NPN and CMP. Homologs of the four lar genes are widely distributed in microorganisms, with some species containing multiple copies of larA whereas others lack this gene, consistent with the cofactor serving other functions. Several LarA-like proteins were shown to catalyze racemase or epimerase activities using 2-hydroxyacid substrates other than lactic acid. Thus, lactate racemase is the founding member of a large family of NPN-containing enzymes.

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Leishmania is an auxotrophic protozoan parasite which acquires D-ribose by transporting it from the host cell and also by the hydrolysis of nucleosides. The enzyme ribokinase (RK) catalyzes the first step of ribose metabolism by phosphorylating D-ribose using ATP to produce D-ribose-5-phosphate. To understand its structure and function, the gene encoding RK from L. donovani was cloned, expressed and purified using affinity and size-exclusion chromatography. Circular-dichroism spectroscopy of the purified protein showed comparatively more α-helix in the secondary-structure content, and thermal unfolding revealed the T to be 317.2 K. Kinetic parameters were obtained by functional characterization of L. donovani RK, and the K values for ribose and ATP were found to be 296 ± 36 and 116 ± 9.0 µM, respectively. Crystals obtained by the hanging-drop vapour-diffusion method diffracted to 1.95 Å resolution and belonged to the hexagonal space group P6, with unit-cell parameters a = b = 100.25, c = 126.77 Å. Analysis of the crystal content indicated the presence of two protomers in the asymmetric unit, with a Matthews coefficient (V) of 2.45 Å Da and 49.8% solvent content. Further study revealed that human counterpart of this protein could be used as a template to determine the first three-dimensional structure of the RK from trypanosomatid parasites.