Effect of allosteric molecules on structure and drug affinity of HIV-1 protease by molecular dynamics simulations.

Recent experiments show that small molecules can bind onto the allosteric sites of HIV-1 protease (PR), which provides a starting point for developing allosteric inhibitors. However, the knowledge of the effect of such binding on the structural dynamics and binding free energy of the active site inhibitor and PR is still lacking. Here, we report 200ns long molecular dynamics simulation results to gain insight into the influences of two allosteric molecules (1H-indole-6-carboxylic acid, 1F1 and 2-methylcyclohexano, 4D9). The simulations demonstrate that both allosteric molecules change the PR conformation and stabilize the structures of PR and the inhibitor; the residues of the flaps are sensitive to the allosteric molecules and the flexibility of the residues is pronouncedly suppressed; the additions of the small molecules to the allosteric sites strengthen the binding affinities of 3TL-PR by about 12-15kal/mol in the binding free energy, which mainly arises from electrostatic term. Interestingly, it is found that the action mechanisms of 1F1 and 4D9 are different, the former behaviors like a doorman that keeps the inhibitor from escape and makes the flaps (door) partially open; the latter is like a wedge that expands the allosteric space and meanwhile closes the flaps. Our data provide a theoretical support for designing the allosteric inhibitor.

Anticancer effect of total annonaceous acetogenins on hepatocarcinoma.

OBJECTIVE: To confirm the anticancer effect of total annonaceous acetogenins (TAAs) abstracted from Annona squamosa Linn. on human hepatocarcinoma. METHODS: The inhibitory effect of TAAs was demonstrated in H22-bearing mice. The potency of TAAs was confirmed as its 50% inhibiting concentration (IC50) on Bel-7402 cell under Sulfur Rhodamine B staining. Both underlying mechanisms were explored as cellular apoptosis and cell cycle under flow cytometry. Mitochondrial and recipient apoptotic pathways were differentiated as mitochondrial membrane potential under flow cytometry and caspases activities under fluorescence analysis. RESULTS: The inhibitory rate of TAAs in mice was 50.98% at 4 mg/kg dose. The IC50 of TAAs on Bel-7402 was 20.06 µg/mL (15.13-26.61µg/mL). Effective mechanisms of TAAs were confirmed as both of arresting cell cycle at G1 phase and inducing apoptosis dose- and time-dependently. Mitochondrial and recipient pathways involved in apoptotic actions of TAAs. CONCLUSION: TAAs is effective for hepatocarcinoma, via inhibiting proliferation and inducing apoptosis.

Huwentoxin-V, a novel insecticidal peptide toxin from the spider Selenocosmia huwena, and a natural mutant of the toxin: indicates the key amino acid residues related to the biological activity.

A neurotoxin peptide (named Huwentoxin-V) was purified from the venom of the Chinese bird spider Selenocosmia huwena by a combination of ion exchange chromatography and reverse phase HPLC. HWTX-V has 35 amino acid residues, and is in perfect agreement with the molecular mass 4111.4 Da identified by mass spectrometry. A natural mutant of the toxin (called mHuwentoxin-V) was also isolated from the venom. mHWTX-V was only truncated two amino acid residues from the C-terminus of HWTX-V, and its molecular weight is 3877.1 Da determined by mass spectrometry. The six cysteine residues in each sequence of the two peptides suggest three disulfide bridges, the present of which was demonstrated by mass spectrometry after dithiothreiotol reduce and S-carboxymethylation. The primary structure of the two toxins exhibits sequence identity with other spider toxins such as ProTx-I (64%), SGTx (57%), SNX-482 (55%), and Hanatoxin (54%). HWTX-V can reversibly paralyze locusts and cockroaches for several hours with a ED50 value as 16 +/- 5 microg/g to locusts, and a larger dose of the toxin can cause death. However, mHWTX-V shows no significant effect on locusts and cockroaches. The structure-activity relationship indicates that the residues Phe34 and Ser35 in the C-terminus of HWTX-V are the key residues of the biological activity.