Hasni Arsad

Structure of polyhydroxyalkanoate (PHA) synthase PhaC from Chromobacterium sp. USM2, producing biodegradable plastics

Polyhydroxyalkanoate (PHA) is a promising candidate for use as an alternative bioplastic to replace petroleum-based plastics. Our understanding of PHA synthase PhaC is poor due to the paucity of available three-dimensional structural information. Here we present a high-resolution crystal structure of the catalytic domain of PhaC from Chromobacterium sp. USM2, PhaCCs-CAT. The structure shows that PhaCCs-CAT forms an α/β hydrolase fold comprising α/β core and CAP subdomains. The active site containing Cys291, Asp447 and His477 is located at the bottom of the cavity, which is filled with water molecules and is covered by the partly disordered CAP subdomain. We designated our structure as the closed form, which is distinct from the recently reported catalytic domain from Cupriavidus necator (PhaCCn-CAT). Structural comparison showed PhaCCn-CAT adopting a partially open form maintaining a narrow substrate access channel to the active site, but no product egress. PhaCCs-CAT forms a face-to-face dimer mediated by the CAP subdomains. This arrangement of the dimer is also distinct from that of the PhaCCn-CAT dimer. These findings suggest that the CAP subdomain should undergo a conformational change during catalytic activity that involves rearrangement of the dimer to facilitate substrate entry and product formation and egress from the active site.

ANTIPROLIFERATIVE EFFECT ON BREAST CANCER (MCF7) OF Moringa oleifera SEED EXTRACTS

Background: Moringa oleifera belongs to plant family, Moringaceae and popularly called “wonderful tree”, for it is used traditionally to cure many diseases including cancer in Africa and Asia, however, there is limited knowledge on cytotoxic activity of Moringa oleifera seeds on MCF7 breast cancer cell. The present study evaluated antiproliferative effect on MCF7 of the seed. Materials and Methods: Seeds of Moringa oleifera were grinded to powder and its phytochemicals were extracted using water and 80% ethanol solvents, part of the ethanolic extract were sequentially partitioned to fractions with four solvents (hexane, dichloromethane, chloroform, and n-butanol). Antiproliferative effects on MCF7 of the samples were determined. Finally, potent samples that significantly inhibited MCF7 growth were tested on MCF 10A. Results: Crude water extract, hexane and dichloromethane fractions of the seeds inhibited the proliferation of MCF7 with the following IC50 values 280 μg/ml, 130 μg/ml and 26 μg/ml respectively, however, of the 3 samples, only hexane fraction had minimal cytotoxic effect on MCF 10A (IC50 > 400μg/ml). Conclusion: Moringa oleifera seed has antiproliferative effect on MCF7.

Biophysical changes of ATP binding pocket may explain loss of kinase activity in mutant DAPK3 in cancer: A molecular dynamic simulation analysis.

DAPK3 belongs to family of DAPK (death-associated protein kinases) and is involved in the regulation of progression of the cell cycle, cell proliferation, apoptosis and autophagy. It is considered as a tumor suppressor kinase, suggesting the loss of its function in case of certain specific mutations. The T112M, D161N and P216S mutations in DAPK3 have been observed in cancer patients. These DAPK3 mutants have been associated with very low kinase activity, which results in the cellular progression towards cancer. However, a clear understanding of the structural and biophysical variations that occur in DAPK3 with these mutations, resulting in the decreased kinase activity has yet not been deciphered. We performed a molecular dynamic simulation study to investigate such structural variations. Our results revealed that mutations caused a significant structural variation in DAPK3, majorly concentrated in the flexible loops that form part of the ATP binding pocket. Interestingly, D161N and P216S mutations collapsed the ATP binding pocket through flexible loops invasion, hindering ATP binding which resulted in very low kinase activity. On the contrary, T112M mutant DAPK3 reduces ATP binding potential through outward distortion of flexible loops. In addition, the mutant lacked characteristic features of the active protein kinase including proper interaction between HR/FD and DFG motifs, well structured hydrophobic spine and Lys42-Glu64 salt bridge interaction. These observations could possibly explain the underlying mechanism associated with the loss of kinase activity with T112M, D161N and P216S mutation in DAPK3.

Molecular docking and dynamic simulation evaluation of Rohinitib - Cantharidin based novel HSF1 inhibitors for cancer therapy.

Recent developments in the target based cancer therapies have identified HSF1 as a novel non oncogenic drug target. The present study delineates the design and molecular docking evaluation of Rohinitib (RHT) - Cantharidin (CLA) based novel HSF1 inhibitors for target-based cancer therapy. Here, we exploited the pharmacophoric features of both the parent ligands for the design of novel hybrid HSF1 inhibitors. The RHT-CLA ligands were designed and characterized for ADME/Tox features, interaction with HSF1 DNA binding domain and their pharmacophoric features essential for interaction. From the results, amino acid residues Ala17, Phe61, His63, Asn65, Ser68, Arg71 and Gln72 were found crucial for HSF1 interaction with the Heat shock elements (HSE). The hybrid ligands had better affinity towards the HSF1 DNA binding domain, in comparison to RHT or CLA and interacted with most of the active site residues. Additionally, the HSF1-ligand complex had a reduced affinity towards HSE in comparison to native HSF1. Based on the results, ligand RC15 and RC17 were non carcinogenic, non mutagenic, completely biodegradable under aerobic conditions, had better affinity for HSF1 (1.132 and 1.129 folds increase respectively) and diminished the interaction of HSF1 with HSE (1.203 and 1.239 folds decrease respectively). The simulation analysis also suggested that the ligands formed a stable complex with HSF1, restraining the movement of active site residues. In conclusion, RHT-CLA hybrid ligands can be used as a potential inhibitor of HSF1 for non-oncogene target based cancer therapy.

Evaluation of genetic diversity of Clinacanthus nutans (Acanthaceaea) using RAPD, ISSR and RAMP markers

Three polymerase chain reaction (PCR) techniques were compared to analyse the genetic diversity of Clinacanthus nutans eight populations in the northern region of Peninsular Malaysia. The PCR techniques were random amplified polymorphic deoxyribonucleic acids (RAPD), inter-simple sequence repeats (ISSR) and random amplified microsatellite polymorphisms (RAMP). Leaf genomic DNA was PCR amplified using 17 RAPD, 8 ISSR and 136 RAMP primers . However, only 10 RAPD primers, 5 ISSR primers and 37 RAMP primers produced reproducible bands. The results were evaluated for polymorphic information content (PIC), marker index (MI) and resolving power (RP). The RAMP marker was the most useful marker compared to RAPD and ISSR markers because it showed the highest average value of PIC (0.25), MI (11.36) and RP (2.86). The genetic diversity showed a high percentage of polymorphism at the species level compared to the population level. Furthermore, analysis of molecular variance revealed that the genetic diversity was higher within populations, as compared to among populations of C. nutans. From the results, the RAMP technique was recommended for the analysis of genetic diversity of C. nutans.

Assessment of three plastid DNA barcode markers for identification of Clinacanthus nutans (Acanthaceae)

This study was conducted to determine the feasibility of using three plastid DNA regions (matK, trnH-psbA, and rbcL) as DNA barcodes to identify the medicinal plant Clinacanthus nutans. In this study, C. nutans was collected at several different locations. Total genomic DNA was extracted, amplified by polymerase chain reaction (PCR), and sequenced using matK, trnH-psbA, and rbcL, primers. DNA sequences generated from PCR were submitted to the National Center for Biotechnology Information’s (NCBI) GenBank. Identification of C. nutans was carried out using NCBI’s Basic Local Alignment Search Tool (BLAST). The rbcL and trnH-psbA regions successfully identified C. nutans with sequencing rates of 100% through BLAST identification. Molecular Evolutionary Genetics Analysis (MEGA) 6.0 was used to analyze interspecific and intraspecific divergence of plastid DNA sequences. rbcL and matK exhibited the lowest average interspecific distance (0.0487 and 0.0963, respectively), whereas trnH-psbA exhibited the highest average interspecific distance (0.2029). The R package Spider revealed that trnH-psbA correctly identified Barcode of Life Data System (BOLD) 96%, best close match 79%, and near neighbor 100% of the species, compared to matK (BOLD 72%; best close match 64%; near neighbor 78%) and rbcL (BOLD 77%; best close match 62%; near neighbor 88%). These results indicate that trnH-psbA is very effective at identifying C. nutans, as it performed well in discriminating species in Acanthaceae.