Structure of a novel form of phosphopantetheine adenylyltransferase from Klebsiella pneumoniae at 2.59 Å resolution.

Phosphopantetheine adenylyltransferase (EC. 2.7.7.3, PPAT) catalyzes the penultimate step of the multistep reaction in the coenzyme A (CoA) biosynthesis pathway. In this step, an adenylyl group from adenosine triphosphate (ATP) is transferred to 4'-phosphopantetheine (PNS) yielding 3'-dephospho-coenzyme A (dpCoA) and pyrophosphate (PPi). PPAT from strain C3 of Klebsiella pneumoniae (KpPPAT) was cloned, expressed and purified. It was crystallized using 0.1 M HEPES buffer and PEG10000 at pH 7.5. The crystals belonged to tetragonal space group P41212 with cell dimensions of a = b = 72.82 Å and c = 200.37 Å. The structure was determined using the molecular replacement method and refined to values of 0.208 and 0.255 for Rcryst and Rfree factors, respectively. The structure determination showed the presence of three crystallographically independent molecules A, B and C in the asymmetric unit. The molecules A and B are observed in the form of a dimer in the asymmetric unit while molecule C belongs to the second dimer whose partner is related by crystallographic twofold symmetry. The polypeptide chain of KpPPAT folds into a ß/α structure. The conformations of the side chains of several residues in the substrate binding site in KpPPAT are significantly different from those reported in other PPATs. As a result, the modes of binding of substrates, phosphopantetheine (PNS) and adenosine triphosphate (ATP) differ considerably. The binding studies using fluorescence spectroscopy indicated a KD value of 3.45 × 10-4 M for ATP which is significantly lower than the corresponding values reported for PPAT from other species.

Structural basis for the oligomerization-facilitated NLRP3 activation.

The NACHT-, leucine-rich-repeat-, and pyrin domain-containing protein 3 (NLRP3) is a critical intracellular inflammasome sensor and an important clinical target against inflammation-driven human diseases. Recent studies have elucidated its transition from a closed cage to an activated disk-like inflammasome, but the intermediate activation mechanism remains elusive. Here we report the cryo-electron microscopy structure of NLRP3, which forms an open octamer and undergoes a ~ 90° hinge rotation at the NACHT domain. Mutations on open octamer's interfaces reduce IL-1ß signaling, highlighting its essential role in NLRP3 activation/inflammasome assembly. The centrosomal NIMA-related kinase 7 (NEK7) disrupts large NLRP3 oligomers and forms NEK7/NLRP3 monomers/dimers which is a critical step preceding the assembly of the disk-like inflammasome. These data demonstrate an oligomeric cooperative activation of NLRP3 and provide insight into its inflammasome assembly mechanism.

Structural basis of the human NAIP/NLRC4 inflammasome assembly and pathogen sensing.

The NLR family caspase activation and recruitment domain-containing 4 (NLRC4) inflammasome is a critical cytosolic innate immune machine formed upon the direct sensing of bacterial infection and in response to cell stress during sterile chronic inflammation. Despite its major role in instigating the subsequent host immune response, a more complete understanding of the molecular events in the formation of the NLRC4 inflammasome in humans is lacking. Here we identify Bacillus thailandensis type III secretion system needle protein (Needle) as a potent trigger of the human NLR family apoptosis inhibitory protein (NAIP)/NLRC4 inflammasome complex formation and determine its structural features by cryogenic electron microscopy. We also provide a detailed understanding of how type III secretion system pathogen components are sensed by human NAIP to form a cascade of NLRC4 protomer through a critical lasso-like motif, a 'lock-key' activation model and large structural rearrangement, ultimately forming the full human NLRC4 inflammasome. These results shed light on key regulatory mechanisms specific to the NLRC4 inflammasome assembly, and the innate immune modalities of pathogen sensing in humans.

Structural and mechanistic insights into the inhibition of respiratory syncytial virus polymerase by a non-nucleoside inhibitor.

The respiratory syncytial virus polymerase complex, consisting of the polymerase (L) and phosphoprotein (P), catalyzes nucleotide polymerization, cap addition, and cap methylation via the RNA dependent RNA polymerase, capping, and Methyltransferase domains on L. Several nucleoside and non-nucleoside inhibitors have been reported to inhibit this polymerase complex, but the structural details of the exact inhibitor-polymerase interactions have been lacking. Here, we report a non-nucleoside inhibitor JNJ-8003 with sub-nanomolar inhibition potency in both antiviral and polymerase assays. Our 2.9 Å resolution cryo-EM structure revealed that JNJ-8003 binds to an induced-fit pocket on the capping domain, with multiple interactions consistent with its tight binding and resistance mutation profile. The minigenome and gel-based de novo RNA synthesis and primer extension assays demonstrated that JNJ-8003 inhibited nucleotide polymerization at the early stages of RNA transcription and replication. Our results support that JNJ-8003 binding modulates a functional interplay between the capping and RdRp domains, and this molecular insight could accelerate the design of broad-spectrum antiviral drugs.

Development of small molecule inhibitors of natural killer group 2D receptor (NKG2D).

Natural killer group 2D (NKG2D) is a homodimeric activating immunoreceptor whose function is to detect and eliminate compromised cells upon binding to the NKG2D ligands (NKG2DL) major histocompatibility complex (MHC) molecules class I-related chain A (MICA) and B (MICB) and UL16 binding proteins (ULBP1-6). While typically present at low levels in healthy cells and tissue, NKG2DL expression can be induced by viral infection, cellular stress or transformation. Aberrant activity along the NKG2D/NKG2DL axis has been associated with autoimmune diseases due to the increased expression of NKG2D ligands in human disease tissue, making NKG2D inhibitors an attractive target for immunomodulation. Herein we describe the discovery and optimization of small molecule PPI (protein-protein interaction) inhibitors of NKG2D/NKG2DL. Rapid SAR was guided by structure-based drug design and accomplished by iterative singleton and parallel medicinal chemistry synthesis. These efforts resulted in the identification of several potent analogs (14, 21, 30, 45) with functional activity and improved LLE.

Septum site placement in Mycobacteria - identification and characterisation of mycobacterial homologues of Escherichia coli MinD.

A major virulence trait of Mycobacterium tuberculosis (M. tb) is its ability to enter a dormant state within its human host. Since cell division is intimately linked to metabolic shut down, understanding the mechanism of septum formation and its integration with other events in the division pathway is likely to offer clues to the molecular basis of dormancy. The M. tb genome lacks obvious homologues of several conserved cell division proteins, and this study was aimed at identifying and functionally characterising mycobacterial homologues of the E. coli septum site specification protein MinD (Ec MinD). Sequence homology based analyses suggested that the genomes of both M. tb and the saprophyte Mycobacterium smegmatis (M. smegmatis) encode two putative Ec MinD homologues - Rv1708/MSMEG_3743 and Rv3660c/ MSMEG_6171. Of these, Rv1708/MSMEG_3743 were found to be the true homologues, through complementation of the E. coli ∆minDE mutant HL1, overexpression studies, and structural comparisons. Rv1708 and MSMEG_3743 fully complemented the mini-cell phenotype of HL1, and over-expression of MSMEG_3743 in M. smegmatis led to cell elongation and a drastic decrease in c.f.u. counts, indicating its essentiality in cell-division. MSMEG_3743 displayed ATPase activity, consistent with its containing a conserved Walker A motif. Interaction of Rv1708 with the chromosome associated proteins ScpA and ParB, implied a link between its septum formation role, and chromosome segregation. Comparative structural analyses showed Rv1708 to be closer in similarity to Ec MinD than Rv3660c. In summary we identify Rv1708 and MSMEG_3743 to be homologues of Ec MinD, adding a critical missing piece to the mycobacterial cell division puzzle.

Structural evidence of the conversion of nitric oxide (NO) to nitrite ion (NO2-) by lactoperoxidase (LPO): Structure of the complex of LPO with NO2- at 1.89 Å resolution.

Lactoperoxidase (LPO) is a heme containing mammalian enzyme which uses hydrogen peroxide (H2O2) to catalyze the conversion of substrates into oxidized products. LPO is found in body fluids and tissues such as milk, saliva, tears, mucosa and other body secretions. The previous structural studies have shown that LPO converts substrates, thiocyanate (SCN-) and iodide (I-) ions into oxidized products, hypothiocyanite (OSCN-) and hypoiodite (IO-) ions respectively. We report here a new structure of the complex of LPO with an oxidized product, nitrite (NO2-). This product was generated from NO using the two step reaction of LPO by adding hydrogen peroxide (H2O2) in the solution of LPO in 0.1 M phosphate buffer at pH 6.8 as the first step. In the second step, NO gas was added to the above mixture. This was crystallized using 20% (w/v) PEG-3350 and 0.2 M ammonium iodide at pH 6.8. The structure determination showed the presence of NO2- ion in the distal heme cavity of the substrate binding site of LPO. The structure also showed that the propionate group which is linked to pyrrole ring D of the heme moiety was disordered. Similarly, the side chain of Asp108, which is covalently linked to heme moiety, was also split into two components. As a result of these changes, the conformation of the side chain of Arg255 was altered allowing it to form new interactions with the disordered carboxylic group of propionate moiety. These structural changes are indicative of an intermediate state in the catalytic reaction pathway of LPO.

Target 2035 - an update on private sector contributions.

Target 2035, an international federation of biomedical scientists from the public and private sectors, is leveraging 'open' principles to develop a pharmacological tool for every human protein. These tools are important reagents for scientists studying human health and disease and will facilitate the development of new medicines. It is therefore not surprising that pharmaceutical companies are joining Target 2035, contributing both knowledge and reagents to study novel proteins. Here, we present a brief progress update on Target 2035 and highlight some of industry's contributions.

Identification of potential anti-mucor agents by targeting endothelial cell receptor glucose-regulated protein-78 using in silico approach.

Mucormycosis is a fungal infection of the sinuses, brain and lungs that is the cause of approximately 50% mortality rate despite the available first-line therapy. Glucose-Regulated Protein 78 (GRP78) is already reported to be a novel host receptor that mediates invasion and damage of human endothelial cells by Rhizopus oryzae and Rhizopus delemar, the most common etiologic species of Mucorales. The expression of GRP78 is also regulated by the levels of iron and glucose in the blood. There are several antifungal drugs in the market but they pose a serious side effect to the vital organs of the body. Therefore, there is an immediate need to discover effective drug molecules having increased efficacy with no side effects. With the help of various computational tools, the current study was attempted to determine potential antimucor agents against GRP78. The receptor molecule GRP78 was screened against 8820 known drugs deposited in DrugBank library using high-throughput virtual screening method. Total top 10 compounds were selected based on the binding energies greater than the reference co-crystal molecule. Furthermore, molecular dynamic (MD) simulations using AMBER were performed to calculate the stability of the top-ranked compounds in the active site of GRP78. After extensive computational studies, we propose that two compounds (CID439153 and CID5289104) have inhibitory potency against mucormycosis and can serve as potential drugs that can form the basis of treating mucormycosis disease.Communicated by Ramaswamy H. Sarma.

Convergence of immune escape strategies highlights plasticity of SARS-CoV-2 spike.

The global spread of the SARS-CoV-2 virus has resulted in emergence of lineages which impact the effectiveness of immunotherapies and vaccines that are based on the early Wuhan isolate. All currently approved vaccines employ the spike protein S, as it is the target for neutralizing antibodies. Here we describe two SARS-CoV-2 isolates with unusually large deletions in the N-terminal domain (NTD) of the spike. Cryo-EM structural analysis shows that the deletions result in complete reshaping of the NTD supersite, an antigenically important region of the NTD. For both spike variants the remodeling of the NTD negatively affects binding of all tested NTD-specific antibodies in and outside of the NTD supersite. For one of the variants, we observed a P9L mediated shift of the signal peptide cleavage site resulting in the loss of a disulfide-bridge; a unique escape mechanism with high antigenic impact. Although the observed deletions and disulfide mutations are rare, similar modifications have become independently established in several other lineages, indicating a possibility to become more dominant in the future. The observed plasticity of the NTD foreshadows its broad potential for immune escape with the continued spread of SARS-CoV-2.

Discovery of arylsulfonamides as a novel class of allosteric integrase inhibitors with antiviral activity.

Lens epithelial-derived growth factor (LEDGF) increases the efficiency of proviral DNA integration into the host genome by interacting with HIV integrase (IN) and directing it to a chromatin environment that favors viral transcription. Allosteric integrase inhibitors (ALLINIs), such as known 2-(tert-butoxy)acetic acid (1), bind to the LEDGF pocket on the catalytic core domain (CCD) of IN, but exert more potent antiviral activities by inhibition of late-stage HIV-1 replication events than through disruption of proviral integration at an earlier phase. A high-throughput screen (HTS) for compounds that disrupt IN-LEDGF interaction led to the identification of a novel arylsulfonamide series, as exemplified by 2, possessing ALLINI-like properties. Further SAR studies led to more potent compound 21 and provided key chemical biology probes revealing that arylsulfonamides are a novel class of ALLINIs with a distinct binding mode than that of 2-(tert-butoxy)acetic acids.

Identification of small-molecule protein-protein interaction inhibitors for NKG2D.

NKG2D (natural-killer group 2, member D) is a homodimeric transmembrane receptor that plays an important role in NK, γδ+, and CD8+ T cell-mediated immune responses to environmental stressors such as viral or bacterial infections and oxidative stress. However, aberrant NKG2D signaling has also been associated with chronic inflammatory and autoimmune diseases, and as such NKG2D is thought to be an attractive target for immune intervention. Here, we describe a comprehensive small-molecule hit identification strategy and two distinct series of protein-protein interaction inhibitors of NKG2D. Although the hits are chemically distinct, they share a unique allosteric mechanism of disrupting ligand binding by accessing a cryptic pocket and causing the two monomers of the NKG2D dimer to open apart and twist relative to one another. Leveraging a suite of biochemical and cell-based assays coupled with structure-based drug design, we established tractable structure-activity relationships with one of the chemical series and successfully improved both the potency and physicochemical properties. Together, we demonstrate that it is possible, albeit challenging, to disrupt the interaction between NKG2D and multiple protein ligands with a single molecule through allosteric modulation of the NKG2D receptor dimer/ligand interface.

Early detection of glomerular dysfunction and renal tubulopathy in children with sickle cell disease in India.

BACKGROUND: Sickle cell disease causes microvascular occlusion in different vascular beds. In kidneys, it leads to occult glomerular dysfunction causing asymptomatic microalbuminuria, proximal tubulopathy causing hyposthenuria and increased free water loss and distal tubulopathy causing poor urine acidification. We studied the prevalence of various types of renal dysfunction, the ability of different tests to detect it at an early stage and the correlation of these parameters in children receiving hydroxyurea (HU). PROCEDURE: Fifty-six children (sample size calculated using SAS9.2 package) attending paediatric clinical services in a tertiary care hospital between 2 and 12 years of age diagnosed by high-performance liquid chromatography (HPLC) were enrolled. Their demographic and laboratory data including renal and urine parameters were collected. Parameters like fractional excretion of sodium (FeNa), trans tubular potassium gradient (TtKg) and free water clearance (TcH2O) were derived by calculations. Data were analysed using IBM SPSS Version 21.0 and Microsoft Office Excel 2007. RESULTS: We found a significant number of children to have microalbuminuria (17.8%), hyposthenuria (30.4%) and impaired renal tubular potassium excretion (TtKg) (81.3%). A significant correlation was found between the dose of HU with urine osmolality (p < 0.0005) and free water clearance (p = 0.002), while all parameters showed a significant correlation with compliance with HU. Derangement in urine microalbumin and TcH2O correlated significantly with low mean haemoglobin levels (<9 g/dl). CONCLUSION: Renal dysfunction is common in children with SCD and can be detected early using simple urine parameters and can be prevented with an early and appropriate dosage of HU with good compliance.

Duvelisib Eliminates CLL B Cells, Impairs CLL-Supporting Cells, and Overcomes Ibrutinib Resistance in a Xenograft Model.

PURPOSE: Inhibitors of Bruton's tyrosine kinase (BTKi) and PI3K (PI3Ki) have significantly improved therapy of chronic lymphocytic leukemia (CLL). However, the emergence of resistance to BTKi has introduced an unmet therapeutic need. Hence, we sought evidence for essential roles of PI3K-δi and PI3K-γi in treatment-naïve and BTKi-refractory CLL. EXPERIMENTAL DESIGN: Responses to PI3K-δi, PI3K-γi, and the dual-inhibitor duvelisib in each B, T, and myeloid cell compartments of CLL were studied in vitro, and in a xenograft mouse model using primary cells from treatment-naïve and ibrutinib-resistant patients, and finally, in a patient with ibrutinib-resistant CLL treated with duvelisib. RESULTS: We demonstrate the essential roles of PI3K-δ for CLL B-cell survival and migration, of PI3K-γ for T-cell migration and macrophage polarization, and of dual inhibition of PI3K-δ,γ for efficacious reduction of leukemia burden. We also show that samples from patients whose disease progressed on ibrutinib were responsive to duvelisib therapy in a xenograft model, irrespective of BTK mutations. In support of this, we report a patient with ibrutinib-resistant CLL, bearing a clone with BTK and PLCγ2 mutations, who responded immediately to single-agent duvelisib with redistribution lymphocytosis followed by a partial clinical remission associated with modulation of T and myeloid cells. CONCLUSIONS: Our data define the mechanism of action whereby dual inhibition of PI3K-δ,γ affects CLL B-cell numbers and T and myeloid cell pro-leukemia functions and support the use of duvelisib as a valuable approach for therapeutic interventions, including for patients refractory to BTKi.

Structure of the complex of camel peptidoglycan recognition protein-S with hexanoic acid reveals novel features of the versatile ligand-binding site at the dimeric interface.

The short peptidoglycan recognition protein (PGRP-S) of the innate immune system recognizes the invading microbes through binding to their cell wall molecules. In order to understand the mode of binding of PGRP-S to bacterial cell wall molecules, the structure of the complex of camel PGRP-S (CPGRP-S) with hexanoic acid has been determined at 2.07 Å resolution. Previously, we had reported the structures of CPGRP-S in the native unbound state as well as in the complexed forms with the components of various bacterial cell wall molecules such as peptidoglycan (PGN), lipopolysaccharide (LPS), lipoteichoic acid (LTA), mycolic acid (MA) and other fatty acids. These structures revealed that CPGRP-S formed two homodimers which were designated as A-B and CD dimers. It also showed that the fatty acids bind to CPGRP-S in the binding site at the A-B dimer while the non-fatty acids were shown to bind at the interfaces of both A-B and CD dimers. The present structure of the complex of CPGRP-S with hexanoic acid (HA) showed that HA binds to CPGRP-S at the interface of CD dimer. HA was located in the same groove at the CD interface which was occupied by non-fatty acids such as PGN, LPS and LTA and interacts with residues from both C and D molecules. HA is firmly held in the groove with several hydrogen bonds and a number of van der Waals contacts. This is the first structure which reports the binding of a fatty acid in the cleft at the interface of CD dimer.

What are the reasons for abandonment of low vision devices prescribed in a large tertiary eye care centre?

PURPOSE: To investigate abandonment rates of near-vision low vision devices (LVDs) and factors that influence abandonment among patients attending a tertiary low vision rehabilitation centre in South India. METHODS: Two hundred and eighty-six adults with low vision completed the modified device abandonment survey 1 year following device prescription. The survey included six questions: possession of device, timing of last use, reasons for abandonment, tasks for which the device was used, payment type and change in quality of life (QoL) from device use. The primary outcome measure was abandonment. Multivariate logistic regression analysis was used to investigate factors for abandonment. RESULTS: Three hundred and twelve near-vision devices were prescribed (mean, 1.09 device per patient.) Stand magnifiers (35%) followed by hand-held magnifiers (24%) were most frequently prescribed. Mean logMAR visual acuity (Snellen) in the better-seeing eye was 0.80 (6/38). Of the prescribed near-vision devices, 22% (95% CI, 17 to 27) were abandoned. Patients who abandoned the device were significantly older than those who did not (49.3 ± 17.2 vs. 43.5 ± 18.1 years; p = 0.03). In multivariable analysis, patients reporting no change in their QoL from device use had higher odds of abandoning the device (OR: 63.97; 95% CI, 23.77 to 172.12). Device-related (31%) and psychological (30%) factors were the most frequent reasons for abandonment. Among device-related issues, the most frequent reason was that patients felt the device was too complex to use (50%) followed by being too cumbersome to use (25%). CONCLUSION: The abandonment rate for near-vision LVDs in South India was comparable with that reported in high-income countries. Patients reporting no change in their QoL had a higher likelihood of abandoning the device compared with those who reported some change. Device-related and psychological factors were the most frequent reasons for abandonment. These results can be used to develop strategies to improve compliance with use of devices.

High dietary iodine intake may contribute to the low death rate from COVID-19 infection in Japan with activation by the lactoperoxidase system.

We draw the attention of readers and governments to the death rate from coronavirus disease 2019 in Japan, continuing as a fraction of that experienced by many other developed nations. We think this is due to the activity of the powerful, protective lactoperoxidase system (LPO) which prevents serious airborne infections. The LPO system requires iodine, which is liberally provided by the typical Japanese diet but lacking in many others. One might consider the Japanese experience an incredibly large, open-label study exhibiting the preventative power of a high-iodine diet. We predict this favourable trend will continue for Japan because deadly variants of the severe, acute respiratory syndrome coronavirus 2 will be with us, forever.

Nanoformulation approach for improved antimicrobial activity of bovine lactoperoxidase.

Lactoperoxidase (LPO) is a glycosylated antimicrobial protein present in milk with a molecular mass of 78 kDa. LPO is included in many biological processes and is well-known to have biocidal actions, acting as an active antibiotic and antiviral agent. The wide spectrum biocidal activity of LPO is mediated via a definite inhibitory system named lactoperoxidase system which plays a potent role in the innate immune response. With the current advancement in nanotechnology, nanoformulations can be developed for stabilizing and potentiating the activity of LPO for several applications. In the research described in this Research Communication, fresh LPO purified from bovine mammary gland secretions was used for nanoparticle synthesis using a simple thermal process at different pH and temperatures. The round-shaped nanoparticles (average size 229 nm) were successfully synthesized at pH 7.0 and a temperature of 75°C. These nanoparticles were tested against four different bacterial species namely S. flexineri, P. aeruginosa, S. aureus, and E. coli. The prepared nanoparticles exhibited strong inhibition of the growth against all four bacterial species as stated by their MIC and ZOI values. These results may help in increasing the efficiency of lactoperoxidase system and will assist in identifying novel avenues to enhance the stability and antimicrobial function of LPO in drug discovery and industrial processes.

Ligand recognition by peptidoglycan recognition protein-S (PGRP-S): structure of the complex of camel PGRP-S with heptanoic acid at 2.15 Å resolution.

Peptidoglycan recognition proteins (PGRPs) are important components of the innate immune system which provide the first line of defense against invading microbes. There are four members in the family of PGRPs in animals of which PGRP-S is a common domain. It is responsible for the binding to microbial cell wall molecules. In order to understand the mode of binding of PGRP-S to the components of the bacterial cell wall, the structure of the complex of camel PGRP-S (CPGRP-S) with heptanoic acid has been determined at 2.15 Å resolution. The structure determination showed the presence of four crystallographically independent protein molecules which are designated as A, B, C, and D. These four protein molecules associate in the form of two homodimers which are represented as A-B and C-D dimers. The association between molecules A and B gives rise to a shallow cleft on the surface at one end of the dimeric interface. One molecule of heptanoic acid is observed at this binding site in the A-B dimer. The association of C and D molecules results in the formation of a long zig-zag tunnel along with the C-D interface. In the cleft at the C-D interface, three molecules of hydrogen peroxide along with other non-water solvent molecules have been observed. The analysis of the several complexes of CPGRP-S with fatty acids and non-fatty acids such as peptidoglycan, lipopolysaccharide, and lipoteichoic acid shows that the fatty acids bind at the A-B site while non-fatty acids interact through C-D interface.

The Mechanism of Action of Lactoferrin - Nucleoside Diphosphate Kinase Complex in Combating Biofilm Formation.

BACKGROUND: The ESKAPE group of pathogens which comprise of multidrug resistant bacteria, namely Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species are the cause of deadly nosocomial infections all over the world. While these pathogens have developed robust strategies to resist most antibiotics, their ability to form biofilms is one of their most combative properties. Hence there is an urgent need to discover new antibacterial agents which could prevent or destroy the biofilms made by these bacteria. Though it has been established that lactoferrin (LF), a potent iron binding antibacterial, antifungal, and antiviral protein displays anti-biofilm properties, its mechanisms of action, in addition to its iron chelation property, still remains unclear. OBJECTIVE: The binding and inhibition studies of LF with the enzyme Nucleoside diphosphate Kinase (NDK) and its elastase cleaved truncated 12 kDa fragment (12-NDK). METHODS: The characterization studies of NDK and 12-NDK using florescence spectroscopy, dynamic light scattering, size exclusion chromatography and ADP-glo Kinase Assay. Inhibition studies of LF-NDK using ADP-glo kinase assay, Surface Plasmon Resonance and Biofilm inhibition studies. RESULTS: NDK and 12-NDK were cloned, expressed and purified from Acinetobacter baumannii and Pseudomonas aeruginosa. The characterization studies revealed NDK and 12-NDK from both species are stable and functional. The inhibition studies of LF-NDK revealed stable binding and inhibition of kinase activity by LF. CONCLUSION: The binding and inhibition studies have shown that while LF binds with both the NDK and their truncated forms, it tends to have a higher binding affinity with the truncated 12 kDa fragments, resulting in their decreased kinase activity. This study essentially gives a new direction to the field of inhibition of biofilm formation, as it proves that LF has a novel mechanism of action in other than iron sequestration.