Mini KMS Activator Ultimate 1.8 Free Download
Sofia Gilcrease
Two regulatory genes, jadR2 and jadR3, in the jadomycin (jad) biosynthetic gene cluster of Streptomyces venezuelae encode homologues of γ-butyrolactone receptor. JadR2 was previously shown to be a pseudo γ-butyrolactone receptor. jadR3 is situated at the upstream of jadW123 encoding putative enzymes for γ-butyrolactone biosynthesis. Disruption of jadR3 resulted in markedly decreased production of jadomycin. Transcriptional analysis revealed that JadR3 represses jadW1, jadR2 and jadR3 but activates jadR1, the key activator gene for jadomycin biosynthesis. DNase I footprinting showed that JadR3 has four binding sites in the intergenic regions of jadR2-jadR1 and jadR3-jadW1. A JadR3 interactive molecule, SVB1, was purified from a large-scale fermentation and its structure found to be the same as SCB3, a γ-butyrolactone from Streptomyces coelicolor, and was absent from a jadW123 mutant lacking jadomycin production. Addition of SVB1 or extract from S. coelicolor to the mutant restored jadomycin production. Overall, our results revealed that the association of JadR3 and SVB1 plays an important role in controlling a regulatory mini-network governing jadomycin biosynthesis, providing new insights into the ways in which γ-butyrolactone/receptor systems modulate antibiotic biosynthesis in Streptomyces.
The mini Activator was inspired by The Activator 3.1 Energy Harmonizer, and carries many of the same potentials and energies of all the Activator line, harmonized into a field of much greater potentials.
SIRT1, the founding member of the mammalian family of seven NAD+-dependent sirtuins, is composed of 747 amino acids forming a catalytic domain and extended N- and C-terminal regions. We report the design and characterization of an engineered human SIRT1 construct (mini-hSIRT1) containing the minimal structural elements required for lysine deacetylation and catalytic activation by small molecule sirtuin-activating compounds (STACs). Using this construct, we solved the crystal structure of a mini-hSIRT1-STAC complex, which revealed the STAC-binding site within the N-terminal domain of hSIRT1. Together with hydrogen-deuterium exchange mass spectrometry (HDX-MS) and site-directed mutagenesis using full-length hSIRT1, these data establish a specific STAC-binding site and identify key intermolecular interactions with hSIRT1. The determination of the interface governing the binding of STACs with human SIRT1 facilitates greater understanding of STAC activation of this enzyme, which holds significant promise as a therapeutic target for multiple human diseases.
Sirtuins are a family of highly conserved NAD+-dependent deacylases that have been linked to a number of important biological processes across a broad span of diverse organisms such as Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophilla melanogaster and Mus musculus, among others1,2. Sirtuins generally catalyze the deacylation of modified lysine residues in protein substrates coupled with the breakdown of NAD+ into nicotinamide (NAM) and 2'-O-acyl-ADP-ribose. Of the seven sirtuins (SIRT1-7) that have been identified in mammals3, human SIRT1 (hSIRT1) is the most studied isoform, and has been shown to be regulated by calorie restriction and to be involved in multiple biological processes4,5,6,7. The validated, protective role of increased mammalian SIRT1 activity in metabolic disorders8, neurodegeneration9 and inflammation10,11 makes this enzyme an attractive therapeutic target. To this end, the development of pharmacological approaches to increase the enzymatic activity of hSIRT1 might lead to a new generation of therapeutic agents for a wide spectrum of diseases associated with aging. Small molecule sirtuin-activating compounds (STAC) have been developed which increase the catalytic deacetylation of specific Lys residues by hSIRT1 in multiple substrates, resulting in a variety of biological responses12,13,14. However, the molecular mechanism of hSIRT1 activation by STACs remains controversial. Questions as to whether STACs directly activate hSIRT1 persist15 despite evidence of allosteric activation13. Recently, a single point mutation of the Glu230 residue of hSIRT1 has been shown to attenuate kinetic activation by STACs16, further demonstrating a direct effect on hSIRT1. Structural characterizations of hSIRT1 fragments have shed light on the inhibitor binding and key regulatory element17,18. Similar to other sirtuins, hSIRT1 catalytic domain contains a Rossmann-fold large lobe and a zinc-binding small lobe and undergoes a significant conformational change of domain closure upon substrate/ligand occupying the active site19,20,21. However, the molecular details governing the binding of STACs to SIRT1 remain elusive, due to the difficulty in obtaining a detailed X-ray crystallographic structure of the full-length enzyme. To address this, we developed an engineered hSIRT1 (mini-hSIRT1) that is biochemically equivalent to the full-length enzyme with respect to basal catalytic activity and activation by STACs. X-ray crystallographic analysis of mini-hSIRT1 resulted in the first detailed structural determination of a fully functional human SIRT1 with a bound small molecule activator. The details of STAC binding to mini-hSIRT1 were translated to the full-length enzyme using structure-guided mutagenesis which corroborated the importance of key amino acids in the binding of STACs. These data are important in elucidating the molecular basis for STAC-mediated activation of hSIRT1 which will be critical for the development of future therapeutic agents.
Interestingly, a STAC-mediated dimer of mini-hSIRT1 related by crystallographic symmetry was observed in the crystal lattices (Fig. 2d). Size exclusion chromatography (SEC) indicates that the apparent size of mini-hSIRT1 increases in the presence of STAC 1, which is likely correspondent to the mini-hSIRT1 dimer species (Supplementary Fig. 4). We are currently attempting to determine if the observed crystallographic dimer has any relevance in the observed biology of STAC-mediated SIRT1 activation.
We used site-directed mutagenesis on the full-length hSIRT1 to confirm the key residues of the SBD that were identified by the mini-hSIRT1 structures. The following point mutants of full-length hSIRT1 were generated probing three classes of residues: (a) residues which appear to directly interact with STACs (T219A, I223A, N226A and I227A); (b) SBD residues with no apparent role in activator binding (Q222A and V224A); and (c) Glu230, previously demonstrated to be important for SIRT1 activation16 (E230K, E230A and E230Q) (Fig. 2b). None of the mutants significantly impaired the basal catalytic activity using the Ac-p53(W5) substrate or affected inhibition by EX-527, a Trifluoroacetic acid (TFA)-p53 peptide (Ac-RHK-KTFA-L-Nle-F-NH2), or NAM (Supplementary Tables 4 and 5).
Asn226 appears to form a hydrogen bond between its carboxamide nitrogen and the carbonyl oxygen of 1 on the surface of the protein (Fig. 2b). However, activation of N226A was only minimally impaired compared with the wild type (Fig. 4a). The small contribution from this H-bond is likely because of its high solvent exposure.
In contrast to the above mutants, Q222A and V224A displayed normal activation which is consistent with their positions away from the STAC in the mini-hSIRT1/1 structure (Fig. 4a and Supplementary Fig. 6b,c). Importantly, all of these data obtained with full-length hSIRT1 are consistent with what the mini-SIRT1 crystal structures predict further validating the biochemical significance of these structures.
Despite the broad impact of the mutations described above, none of them completely abolished activation of hSIRT1 as seen with removal of the SBD. As Ile223 lies directly beneath the bound STAC and activation of I223A is highly compound-dependent, we reasoned that further mutating this residue, to incorporate a more disruptive interaction in hSIRT1, would result in a more highly activation-impaired full-length enzyme. To test this hypothesis, we prepared an I223R mutant to introduce steric bulk and charge into the hydrophobic STAC-binding site. Consistent with our hypothesis, activation is completely lost for all 246 activators using both the Ac-p53(W5) or FOXO-3a substrate peptides (Fig. 4b and Supplementary Fig. 6d), while the basal catalytic activity and inhibition by EX-527, TFA-p53 peptide or NAM is not impacted in the I223R mutant (Supplementary Tables 4, 5 and 8). SEC of the STAC-binding deficient mini-hSIRT1 I223R mutant remains the same in the presence of STAC 1, confirming that the observed mini-hSIRT1 dimerization in solution is mediated by STAC 1. (Supplementary Fig. 4).
Mutation of Glu230 to either Lys or Ala has been recently reported to broadly impair activation by STACs, although the mechanism by which this occurs is unclear16. We tested activation of E230K, E230A and E230Q full-length hSIRT1 proteins and found that the maximum activation is impaired with a minimal impact on the EC50 (Supplementary Tables 6 and 7), suggesting a role for Glu230 in the formation or stabilization of the activated conformation of hSIRT1. Activation of E230Q is also broadly impaired indicating that the negative charge of Glu230 is important for stabilizing the activated conformation of hSIRT1 and likely interacts with a positively charged residue in the activated state.
The observation that regions outside STAC-binding site and substrate-binding site show minimal perturbation in HDX-MS in the presence of both ligands suggests the possibility that the two binding sites might be physically close to each other in the activated conformation. Given this observation and the importance of the negative charge of Glu230 for activation, we postulated that Arg446 located at the active site might be a possible electrostatic partner for Glu230, stabilizing the activated conformation of hSIRT1 and mediating the observed coupling. To this end, we made the mini-hSIRT1 R446E/E230K double mutant with E230K and R446E mini-hSIRT1 as controls. Mini-hSIRT1(E230K) mutant does not affect the basal catalytic activity using the Ac-p53(W5) substrate, as observed in full-length SIRT1 (Supplementary Table 2). Both mini-hSIRT1(R446E) mutant and mini-hSIRT1(E230K,R446E) mutant show higher KM values for both peptide substrate and NAD+, which might result from the potential hydrophobic interaction between the aliphatic part of Arg446 side chain and the substrate as R446F mutant does not affect the basal catalytic activity (Supplementary Table 2). Whereas either E230K or R446E results in significant attenuation of STAC activation of mini-hSIRT1, the E230K,R446E double mutant partially restores STAC-mediated activation of mini-hSIRT1 compared with E230K or R446E, supporting the importance of potential electrostatic interaction between Glu230 and Arg446 in the activated conformation (Fig. 5b,c).
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