Towards a New Biomarker for Diabetic Retinopathy: Exploring RBP3 Structure and Retinoids Binding for Functional Imaging of Eyes In Vivo.

Diabetic retinopathy (DR) is a severe disease with a growing number of afflicted patients, which places a heavy burden on society, both socially and financially. While there are treatments available, they are not always effective and are usually administered when the disease is already at a developed stage with visible clinical manifestation. However, homeostasis at a molecular level is disrupted before visible signs of the disease are evident. Thus, there has been a constant search for effective biomarkers that could signal the onset of DR. There is evidence that early detection and prompt disease control are effective in preventing or slowing DR progression. Here, we review some of the molecular changes that occur before clinical manifestations are observable. As a possible new biomarker, we focus on retinol binding protein 3 (RBP3). We argue that it displays unique features that make it a very good biomarker for non-invasive, early-stage DR detection. Linking chemistry to biological function and focusing on new developments in eye imaging and two-photon technology, we describe a new potential diagnostic tool that would allow rapid and effective quantification of RBP3 in the retina. Moreover, this tool would also be useful in the future to monitor therapeutic effectiveness if levels of RBP3 are elevated by DR treatments.

Regulation of futile ligation during early steps of BER in M. tuberculosis is carried out by a ß-clamp-XthA-LigA tri-component complex.

The Class-II AP-endonuclease (XthA) is a mycobacterial DNA base excision repair (BER) pathway enzyme that functions in the initial steps. It acts on DNA substrates that contain abasic sites to create nicks with 3'-hydroxyl (OH) and 5'-deoxyribose phosphate (5'-dRP) moieties. The NAD+-dependent DNA ligase (LigA) is the terminal player in mycobacterial BER and seals such nicks efficiently. Here, we demonstrate that the Mtbß-clamp-MtbXthA complex that exists in the initial steps of BER engages with MtbLigA to form a novel tri-component BER complex. Size exclusion chromatography (SEC) experiments analysis show that the three proteins interact with equimolar stoichiometry. Small angle X-ray scattering (SAXS) analysis and associated studies reveal that the apo tri-component BER-complex adopts an extended conformation where MtbXthA is sandwiched between the Mtbß-clamp and MtbLigA. The studies support that in the apo-complex MtbXthA binds subsite-I of Mtbß-clamp through 239QLRFPKK245 motif and to MtbLigA by 104DGQPSWSGKP113 motif simultaneously. However, the complex adopts a less-extended conformation in the presence of substrate DNA, where MtbXthA interactions switch from predominantly subsite-I to subsite-II of the Mtbß-clamp. Overall, the novel tri-component complex prevents futile ligation activity of MtbLigA on the product of MtbXthA and ensures forward progression of the pathway and productive mycobacterial BER interactions.

Two-photon excitation fluorescence in ophthalmology: safety and improved imaging for functional diagnostics.

Two-photon excitation fluorescence (TPEF) is emerging as a powerful imaging technique with superior penetration power in scattering media, allowing for functional imaging of biological tissues at a subcellular level. TPEF is commonly used in cancer diagnostics, as it enables the direct observation of metabolism within living cells. The technique is now widely used in various medical fields, including ophthalmology. The eye is a complex and delicate organ with multiple layers of different cell types and tissues. Although this structure is ideal for visual perception, it generates aberrations in TPEF eye imaging. However, adaptive optics can now compensate for these aberrations, allowing for improved imaging of the eyes of animal models for human diseases. The eye is naturally built to filter out harmful wavelengths, but these wavelengths can be mimicked and thereby utilized in diagnostics via two-photon (2Ph) excitation. Recent advances in laser-source manufacturing have made it possible to minimize the exposure of in vivo measurements within safety, while achieving sufficient signals to detect for functional images, making TPEF a viable option for human application. This review explores recent advances in wavefront-distortion correction in animal models and the safety of use of TPEF on human subjects, both of which make TPEF a potentially powerful tool for ophthalmological diagnostics.

COVID-19 retreats and world recovers: A silver lining in the dark cloud.

The coronavirus disease (COVID-19), which the World Health Organization classified as the Sixth Public Health Emergency Of International Concern (PHEIC) on January 30, 2020, is no longer a PHEIC. Millions were affected due to unawareness. The increase in fatalities and shortage of medicine was the first outrage of COVID-19. As per the Johns Hopkins COVID-19 resource center database, it was observed that the disease has spread dynamically across 200+ nations worldwide affecting more than 600 million people from 2019 to 2023, and over thousands of people were victimized regularly at a 2% mortality rate (approx.). In the midway, the mutant variants of concern like omicron, and delta have also created havoc and caused significant impact on public health, global economy, and lifestyle. Since 2019, 3 years now passed and the dynamic disease statistics seem decelerated; moreover, the prevalence of COVID-19 is also fading. The Johns Hopkins resource center has also stopped recording the data of the global pandemic recently from March 10, 2023. Hence, based on the facts, we are presenting a concise report on the pandemic from 2019 to 2023, which includes a brief discussion of the global pandemic. We have highlighted global epidemiology, emphasizing the Indian COVID scenario, vaccination across the globe, and the psychosocial and geopolitical consequences of COVID-19 with a brief background to pathology, clinical management, and the worldwide response against triage. A lot has changed and still needs to change after three tough years of COVID-19. Even though science has progressed and advanced research in medicine is pointing toward future generations, there is no standard care supplied for COVID-19-like calamities. COVID-19 cases might have declined but its influence on the society is still stagnant. This COVID experience has taught us that, despite our bleak beginnings, there is always hope for the future and that we must act with foresight to improve things for future generations.

Salt bridges at the subdomain interfaces of the adenylation domain and active-site residues of Mycobacterium tuberculosis NAD+-dependent DNA ligase A (MtbLigA) are important for the initial steps of nick-sealing activity.

NAD+-dependent DNA ligase (LigA) is the principal bacterial ligase and catalyses a multistep ligation reaction. The adenylation (AdD) domain at the N-terminus consists of subdomains 1a and 1b, where subdomain 1a is unique to LigA. Small-angle X-ray scattering and X-ray diffraction studies were used to probe changes in the relative spatial dispositions of the two subdomains during the adenylation reaction. Structural analyses of the inter-subdomain interactions of the AdD domain suggest that salt bridges formed by Glu22, Glu26 and Glu87 of subdomain 1a with Arg144, Arg315 and His240 of subdomain 1b play an important role in stabilizing the intermediate conformations of the two subdomains. E22A, E26A and E87A mutations reduce the in vitro activity by 89%, 64% and 39%, respectively, on a nicked DNA substrate, while they show no activity loss on a pre-adenylated DNA substrate, thus suggesting that the salt bridges are important in the initial steps of the ligation reaction. Furthermore, the E22A, E26A and E87A mutants exhibited extremely delayed growth in complementation assays involving the Escherichia coli GR501 strain, which harbours its own temperature-sensitive LigA. The H236A and H236Y mutants, which involve the residue that stacks against the adenine moiety of AMP, severely impact the activity and the ability to complement the growth-defective E. coli GR501 strain. Analysis of the K123A and K123R mutations in the active site rationalizes their total loss of activity and inability to rescue the growth-defective E. coli GR501 strain.

Structure based identification of first-in-class fragment inhibitors that target the NMN pocket of M. tuberculosis NAD+-dependent DNA ligase A.

NAD+-dependent DNA ligase (LigA) is the essential replicative ligase in bacteria and differs from ATP-dependent counterparts like the human DNA ligase I (HligI) in several aspects. LigA uses NAD+ as the co-factor while the latter uses ATP. Further, the LigA carries out enzymatic activity with a single divalent metal ion in the active site while ATP-dependent ligases use two metal ions. Instead of the second metal ion, LigA have a unique NMN binding subdomain that facilitates the orientation of the ß-phosphate and NMN leaving group. LigA are therefore attractive targets for new anti-bacterial therapeutic development. Others and our group have earlier identified several LigA inhibitors that mainly bind to AMP binding site of LigA. However, no inhibitor is known to bind to the unique NMN binding subdomain. We initiated a fragment inhibitor discovery campaign against the M. tuberculosis LigA based on our co-crystal structure of adenylation domain with AMP and NMN. The study identified two fragments, 4-(4-fluorophenyl)-4,5,6,7-tetrahydro-3H imidazo[4,5-c] pyridine and N-(4-methylbenzyl)-1H-pyrrole-2-carboxamide, that bind to the NMN site. The fragments inhibit LigA with IC50 of 16.9 and 28.7 µM respectively and exhibit MIC of ~20 and 60 µg/ml against a temperature sensitive E. coli GR501 ligAts strain, rescued by MtbLigA. Co-crystal structures of the fragments with the adenylation domain of LigA show that they mimic the interactions of NMN. Overall, our results suggest that the NMN binding-site is a druggable target site for developing anti-LigA therapeutic strategies.