Helix forming tendency of valine substituted poly-alanine: a molecular dynamics investigation

Modulatory effects of point-mutated IL-32θ (A94V) on tumor progression in triple-negative breast cancer cells

Breast cancer is a frequently diagnosed cancer and the leading cause of death among women worldwide. Tumor-associated macrophages stimulate cytokines and chemokines, which induce angiogenesis, metastasis, proliferation, and tumor-infiltrating immune cells. Although interleukin-32 (IL-32) has been implicated in the development and modulation of several cancers, its function in breast cancer remains elusive. Mutation of interleukin-32θ (IL-32θ) in the tissues of patients with breast cancer was detected by Sanger sequencing. RT-qPCR was used to detect the mRNA levels of inflammatory cytokines, chemokines, and mediators. The secreted proteins were detected using respective enzyme-linked immunosorbent assays. Evaluation of the inhibitory effect of mutant IL-32θ on proliferation, migration, epithelial-mesenchymal transition (EMT), and cell cycle arrest in breast cancer cells was conducted using MTS assays, migration assays, and Western blotting. A point mutation (281C>T, Ala94Val) was detected in IL-32θ in both breast tumors and adjacent normal tissues, which suppressed the expression of pro-inflammatory factors, EMT factors, and cell cycle related factors. Mutated IL-32θ inhibited the expression of inflammatory factors by regulating the NF-κB pathway. Furthermore, mutated IL-32θ suppressed EMT markers and cell cycle related factors through the FAK/PI3K/AKT pathway. It was inferred that mutated IL-32θ modulates breast cancer progression. Mutated IL-32θ (A94V) inhibited inflammation, EMT, and proliferation in breast cancer by regulating the NF-κB (p65/p50) and FAK-PI3K-GSK3 pathways.

Helical Structure of Recombinant Melittin

Melittin is an extensively studied, 26-residue toxic peptide from honey bee venom. Because of its versatility in adopting a variety of secondary (helix or coil) and quaternary (monomer or tetramer) structures in various environments, melittin has been the focus of numerous investigations as a model peptide in protein folding studies as well as in studies involving binding to proteins, lipids, and polysaccharides. A significant body of evidence supports the view that melittin binds to these macromolecules in a predominantly helical conformation, but detailed structural knowledge of this conformation is lacking. In this report, we present nuclear magnetic resonance (NMR)-based structural insights into the helix formation of recombinant melittin in the presence of trifluoroethanol (TFE): a known secondary structure inducer in peptides. These studies were performed at neutral pH, with micromolar amounts of the peptide. Using nuclear Overhauser effect (NOE)-derived distance restraints from three-dimensional NMR spectra, we determined the atomic resolution solution NMR structure of recombinant melittin bearing a TFE-stabilized helix. To circumvent the complications with structure determination of small peptides with high conformational flexibility, we developed a workflow for enhancing proton NOEs by increasing the viscosity of the medium. In the TFE-containing medium, recombinant monomeric melittin forms a long, continuous helical structure, which consists of the N- and C-terminal α-helices and the noncanonical 3₁₀-helix in the middle. The noncanonical 3₁₀-helix is missing in the previously solved X-ray structure of tetrameric melittin and the NMR structure of melittin in methanol. Melittin's structure in TFE-containing medium provides insights into melittin's conformational transitions, which are relevant to the peptide's interactions with its biological targets.

Nanoscale defolding influence of polypeptides in the charge-transfer process through an organic-inorganic nanohybrid system

A biologically important polypeptide [with an alternate sequence of alanine (ALA) and 2-aminobutyric acid (AiB)] is used as a linker molecule to investigate the charge-transfer phenomenon between CdSe nanoparticle (NP) (diameter ∼6-7 nm) assemblies and gold (Au) substrates. The (ALA-AiB)n polypeptides, with varying chain lengths n = 5, 8, 11, were attached to the surface to form self-assembled monolayers (SAMs) through a thiol group located either at the N-terminal or C-terminal of the sequence. Temperature dependent photoluminescence (PL) spectra showed anomalous behavior in the quenching regime of CdSe NPs in the 237 K to 290 K region. In principle, the fluorescence intensity of any fluorophore decreases with a gradual increase in temperature, due to dominating non-radiative relaxation over radiative relaxation. PL spectral intensity follows this general trend from 77 K to 237 K for all chain lengths. For chain length n > 5 (n = 5 showed a kink, but the extent of the kink is negligible in comparison with n > 5) polypeptide-based monolayers, there is a sudden increase in fluorescence intensity above 237 K. This sudden increase is probed using molecular dynamics simulations which reveals that this unprecedented behavior arises due to interchain polypeptide interactions. An insertion of an alkyl chain with an almost similar length of peptide along with polypeptide (in a 3 : 1 ratio, in terms of concentration) diminishes the interchain polypeptide hydrogen-bonding interactions and manifests the normal trend of PL spectra.

Hydroxyproline-containing collagen peptide derived from the skin of the Alaska pollack inhibits HIV-1 infection

The human immunodeficiency virus (HIV) is a lentivirus that results in acquired immunodeficiency syndrome (AIDS). HIV treatment involving chemical therapeutic agents has improved the quality of life of HIV/AIDS patients. The present study demonstrates that a hydroxyproline-containing marine collagen peptide (APHCP) derived from Alaska pollack inhibits HIV‑1 infection in the MT-4 human T cell‑line. APHCP inhibited HIV-1IIIB-induced cell lysis, syncytia formation, reverse transcriptase activity and viral p24 production at non‑cytotoxic concentrations; however, APHCP did not inhibit HIV‑2ROD infection in MT‑4 cells. This suggests that the anti‑HIV activity of APHCP is specific to HIV‑1. In addition, substitution of hydroxyproline residues in APHCP with prolines impaired its anti‑HIV‑1 activity, suggesting that the hydroxyl group of hydroxyprolines is required for the anti‑HIV‑1 activity of APHCP. These results suggested that the marine peptide APHCP may be a novel drug candidate in the development of next‑generation therapeutic agents for the treatment of HIV/AIDS.

Functional consequences of substitution mutations in MepR, a repressor of the Staphylococcus aureus MepA multidrug efflux pump gene

The expression of mepA, encoding the Staphylococcus aureus MepA multidrug efflux protein, is repressed by the MarR homologue MepR. MepR dimers bind differently to operators upstream of mepR and mepA, with affinity being greatest at the mepA operator. MepR substitution mutations may result in mepA overexpression, with A103V most common in clinical strains. Evaluation of the functional consequences of this and other MepR substitutions using a lacZ reporter gene assay revealed markedly reduced repressor activity in the presence of Q18P, F27L, G97E, and A103V substitutions. Reporter data were generally supported by susceptibility and efflux assays, and electrophoretic mobility shift assays (EMSAs) confirmed compromised affinities of MepR F27L and A103V for the mepR and mepA operators. One mutant protein contained two substitutions (T94P and T132M); T132M compensated for the functional defect incurred by T94P and also rescued that of A103V but not F27L, establishing it as a limited-range suppressor. The function of another derivative with 10 substitutions was minimally affected, and this may be an extreme example of suppression involving interactions among several residues. Structural correlations for the observed functional effects were ascertained by modeling mutations onto apo-MepR. It is likely that F27L and A103V affect the protein-DNA interaction by repositioning of DNA recognition helices. Negative functional consequences of MepR substitution mutations may result from interference with structural plasticity, alteration of helical arrangements, reduced protein-cognate DNA affinity, or possibly association of MepR protomers. Structural determinations will provide further insight into the consequences of these and other mutations that affect MepR function, especially the T132M suppressor.