Kakeromamide A,a new cyclic pentapeptide inducing astrocyte differentiation isolated from the marine cyanobacterium Moorea bouillonii

Kakeromamide A (1), a new cyclic pentapeptide encompassing a thiazole ring moiety and a β-amino acid, was isolated from the marine cyanobacterium Moorea bouillonii. Its structure was elucidated by the spectral analysis and the modified Marfey’s method. Compound 1 induced differentiation of neural stem cells into astrocytes at the concentration of 10?µM.     

Impact of the green tea ingredient epigallocatechin gallate and a short pentapeptide (Ile-Ile-Ala-Glu-Lys) on the structural organization of mixed micelles and the related uptake of cholesterol

Background

High levels of blood cholesterol are conventionally linked to an increased risk of developing cardiovascular disease (Grundy, 1986). Here we examine the molecular mode of action of natural products with known cholesterol-lowering activity, such as for example the green tea ingredient epigallocatechin gallate and a short pentapeptide, Ile-Ile-Ala-Glu-Lys.

Stability, denaturation and refolding of Mycobacterium tuberculosis MfpA, a DNA mimicking protein that confers antibiotic resistance

MfpA from Mycobacterium tuberculosis is a founding member of the pentapeptide repeat class of proteins (PRP) that is believed to confer bacterial resistance to the drug fluoroquinolone by mimicking the size, shape and surface charge of duplex DNA. We show that phenylalanine side chain stacking stabilizes the N-terminus of MfpA's pentapeptide thus extending the DNA mimicry analogy. The Lumry-Eyring model was applied to multiple spectral measures of MfpA denaturation revealing that the MfpA dimer dissociates to monomers which undergo a structural transition that leads to aggregation. MfpA retains high secondary and tertiary structure content under denaturing conditions. Dimerization stabilizes MfpA's pentapeptide repeat fold. The high Arrhenius activation energy of the barrier to aggregate formation rationalizes its stability. The mechanism of MfpA denaturation and refolding is a ‘double funnel’ energy landscape where the ‘native’ and ‘aggregate’ funnels are separated by the high barrier that is not overcome during in vitro refolding.     

Biologically active analogs of thymopentin with enhanced enzymatic stability

Thymopentin, a synthetic pentapeptide fragment of thymopoietin (residues 32–36, Arg-Lys-Asp-Val-Tyr) is biologically active but susceptible to proteolytic digestion. Analogs were synthesized and studied for biological activity and susceptibility to peptidases. Amino acid changes were incorporated at positions known to not affect activity adversely and N-terminal acetylation and C-terminal amidation were used to increase resistance to proteolytic degradation by exopeptidases. Ac-Pro²-TP5-NH₂ and Aib²-TP5-NH₂ retained activity and were shown to exhibit a high degree of stability when incubated in human serum.     

Identification and characterization of novel immunomodulatory bursal-derived pentapeptide-II (BPP-II)

The bursa of Fabricius, the acknowledged central humoral immune organ, plays a vital role in B lymphocyte differentiation. However, there are few reports of the molecular basis of the mechanism on immune induction and potential antitumor activity of bursal-derived peptides. In this paper, a novel bursal-derived pentapeptide-II (BPP-II, MTLTG) was isolated and exerted immunomodulatory functions on antibody responses in vitro. Gene microarray analyses demonstrated that BPP-II regulated expression of 2478 genes in a mouse-derived hybridoma cell line. Immune-related gene ontology functional procedures were employed for further functional analysis. Furthermore, the majority of BPP-II-regulated pathways were associated with immune responses and tumor processes. Moreover, BPP-II exhibited immunomodulatory effects on antigen-specific immune responses in vivo, including enhancement of avian influenza virus (H9N2 subtype)-specific antibody and cytokine production and modification of T cell immunophenotypes and lymphocyte proliferation. Finally, BPP-II triggered p53 expression and stabilization and selectively inhibited tumor cell proliferation. These data identified the multifunctional factor, BPP-II, as a novel biomaterial representing an important linking between the humoral central immune system and immune induction, including antitumor. Information generated in this study elucidates further the mechanisms involved in humoral immune system and represents the potential basis of effective immunotherapeutic strategies for treating human tumors and immune improvement.     

The evolution of protein sequences by repetitious gene duplication: Clostridial flavodoxin

Summary Internal regularities of amino acid sequences of flavodoxins, FMN-containing, low molecular weight flavoproteins, were statistically examined using the minimum mutation method. The sequence ofClostridium pasteurianum flavodoxin shows statistically significant evidence of repetitious internal gene duplications at different levels of structure. Peptide pairs with a low chance probability of occurrence were frequently observed at a shift of 5 residues. The pairs with the lowest chance probabilites are a pair of heptapeptides at positions 39–45 vs. 44–50, a 5 residue shift (p = 9 × 10^–6). Most of the related pairs are consistent and could best be explained by the repeating pentapeptide sequence: (Lys-Gly-Ala-Asp-Val-)_n and appropriate gaps. Internal repetitions with longer shifts were also suggested for other flavodoxins. Repetitious gene duplication is proposed for the early stages of flavodoxin evolution.     

Pentapeptide boronic acid inhibitors of Mycobacterium tuberculosis MycP1 protease

Mycosin protease-1 (MycP₁) cleaves ESX secretion-associated protein B (EspB) that is a virulence factor of Mycobacterium tuberculosis, and accommodates an octapeptide, AVKAASLG, as a short peptide substrate. Because peptidoboronic acids are known inhibitors of serine proteases, the synthesis and binding of a boronic acid analog of the pentapeptide cleavage product, AVKAA, was studied using MycP₁ variants from Mycobacterium thermoresistible (MycP_1mth), Mycobacterium smegmatis (MycP_1msm) and M. tuberculosis (MycP_1mtu). We synthesized the boropentapeptide, HAlaValLysAlaAlaB(OH)₂ (1) and the analogous pinanediol PD-protected HAlaValLysAlaAlaBO₂(PD) (2) using an Fmoc/Boc peptide strategy. The pinanediol boropentapeptide 2 displayed IC₅₀ values 121.6 ± 25.3 μM for MycP_1mth, 93.2 ± 37.3 μM for MycP_1msm and 37.9 ± 5.2 μM for MycP_1mtu. Such relatively strong binding creates a chance for crystalizing the complex with 2 and finding the structure of the unknown MycP₁ catalytic site that would potentially facilitate the development of new anti-tuberculosis drugs.     

Thioredoxin targets of the plant chloroplast lumen and their implications for plastid function

The light‐dependent regulation of stromal enzymes by thioredoxin (Trx)‐catalysed disulphide/dithiol exchange is known as a classical mechanism for control of chloroplast metabolism. Recent proteome studies show that Trx targets are present not only in the stroma but in all chloroplast compartments, from the envelope to the thylakoid lumen. Trx‐mediated redox control appears to be a common feature of important pathways, such as the Calvin cycle, starch synthesis and tetrapyrrole biosynthesis. However, the extent of thiol‐dependent redox regulation in the thylakoid lumen has not been previously systematically explored. In this study, we addressed Trx‐linked redox control in the chloroplast lumen of Arabidopsis thaliana. Using complementary proteomics approaches, we identified 19 Trx target proteins, thus covering more than 40% of the currently known lumenal chloroplast proteome. We show that the redox state of thiols is decisive for degradation of the extrinsic PsbO1 and PsbO2 subunits of photosystem II. Moreover, disulphide reduction inhibits activity of the xanthophyll cycle enzyme violaxanthin de‐epoxidase, which participates in thermal dissipation of excess absorbed light. Our results indicate that redox‐controlled reactions in the chloroplast lumen play essential roles in the function of photosystem II and the regulation of adaptation to light intensity.     

Effect of deletion of a plant like pentapeptide insert on kinetic, structural and immunological properties of enolase from Plasmodium falciparum

Plasmodium falciparum enolase (Pfen) is of photosynthetic lineage as evident from the presence of a plant like pentapeptide insert ¹⁰⁴EWGWS¹⁰⁸ in a highly conserved surface loop of the protein. Such a unique region which is absent in human enolase, constitutes an excellent target for inhibitor design, provided its essentiality for function could be demonstrated. A deletion Pfen lacking this insert was made and the effect of this deletion on activity and structure was assessed. Deletion of insert resulted in ∼100-fold decrease in k_cat/K_m and caused dissociation of dimeric form into monomers. Since the parasite enolase localizes on the merozoite surface and confers partial protection against malaria [I. Pal-Bhowmick, M. Mehta, I. Coppens, S. Sharma, G.K. Jarori, Infect. Immun. 75 (11) (2007) 5500-5008], the possibility of the insert being involved in protective response was examined. Serum from Pfen vaccinated mouse which showed prolonged survival to parasite challenge had negligible reactivity against deletion protein as compared to wild type enolase. These results indicate that the insert sequence is required for the full enolase activity and may constitute the protective antigenic epitope in parasite enolase.