On the structural affinity of macromolecules with different biological properties: molecular dynamics simulations of a series of TEM-1 mutants.

Molecular Dynamics simulations have been carried out in order to provide a molecular rationalization of the biological and thermodynamic differences observed for a class of TEM ß-lactamases. In particular we have considered the TEM-1(wt), the single point mutants TEM-40 and TEM-19 representative of IRT and ESBL classes respectively, and TEM-1 mutant M182T, TEM-32 and TEM-20 which differ from the first three for the additional of M182T mutation. Results indicate that most of the thermodynamic, and probably biological behaviour of these systems arise from subtle effects which, starting from the alterations of the local interactions, produce drastic modifications of the conformational space spanned by the enzymes. The present study suggests that systems showing essentially the same secondary and tertiary structure may differentiate their chemical-biological activity essentially (and probably exclusively) on the basis of the thermal fluctuations occurring in their physiological environment.

Conformational study of bovine lactoferricin in membrane-micking conditions by molecular dynamics simulation and circular dichroism.

Lactoferricins are potent antimicrobial peptides released by pepsin cleavage of Lactoferrins. Bovine Lactoferricin (LfcinB) has higher activity than the intact bovine Lactoferrin, and is the most active among the other Lactoferricins of human, murine and caprine origin. In the intact protein the fragment corresponding to LfcinB is in an helical conformation, while in water LfcinB adopts an amphipathic ß-hairpin structure. However, whether any of these structural motifs is the antibacterial active conformation, i.e., the one interacting with bacterial membrane components, remains to be seen. Here we present Circular Dichroism (CD) spectra and Molecular Dynamics (MD) simulations indicating that in membrane-mimicking solvents the LfcinB adopts an amphipathic ß-hairpin structure similar to that observed in water, but differing in the dynamic behavior of the side-chains of the two tryptophan residues. In the membrane-mimicking solvent these side-chains show a high propensity to point towards the hydrophobic environment, rather than being in the hydrophobic core as seen in water, while the backbone preserves the hairpin conformation as found in water. These results suggest that the tryptophans might act as anchors pulling the stable, solvent-invariant hairpin structure into the membrane.

1,3-Dialkyl-8-(hetero)aryl-9-OH-9-deazaxanthines as potent A2B adenosine receptor antagonists: design, synthesis, structure-affinity and structure-selectivity relationships.

A number of 1,3-dialkyl-8-(hetero)aryl-9-OH-9-deazaxanthines were prepared and evaluated as ligands of recombinant human adenosine receptors (hARs). Several 1,3-dipropyl derivatives endowed with nanomolar binding affinity at hA(2B) receptors, but poor selectivity over hA(2A), hA(1) and hA(3) AR subtypes were identified. A comparison with the corresponding 7-OH- and 7,9-unsubstituted-deazaxanthines revealed that 9-OH-9-deazaxanthines are more potent hA(2B) ligands with lower partition coefficients and higher water solubility compared to the other two congeneric classes of deazaxanthines. An optimization of the para-substituent of the 8-phenyl ring of 9-OH-9-deazaxanthines led to the discovery of compound 38, which exhibited outstanding hA(2B) affinity (Ki=1.0 nM), good selectivity over hA(2A), hA(1) and hA(3) (selectivity indices=100, 79 and 1290, respectively) and excellent antagonist potency in a functional assay on rat A(2B) (pA(2B)=9.33).

Stereoselectivity by enantiomeric inhibitors of matrix metalloproteinase-8: new insights from molecular dynamics simulations.

Molecular Dynamics simulations in aqueous solution were performed for the matrix metalloproteinase-8 (MMP-8) free catalytic domain and for its complexes with the (R)- and (S)-[1-(4'-methoxybiphenyl-4-sulfonylamino)-2-methylpropyl] phosphonate. The 144-155 loop of the enzyme undergoes a drastic decrease of mobility once complexed with both enantiomers. The two enantiomers induce a different decrease of conformational entropy upon complexation. The higher affinity of the R-enantiomer can be related to the lower loss of conformational entropy accompanying its binding. The differences in the dynamical behavior of the protein induced by the two enantiomers are discussed at molecular level and the mode of binding of the simulated complexes is compared with that previously determined by X-ray crystallography.

Molecular dynamics simulation of Leishmania major surface metalloprotease GP63 (leishmanolysin).

One of the molecular factors contributing to Leishmania sp. virulence and pathogenesis is the major surface metalloprotease GP63, alternatively called leishmanolysin, MSP, and PSP (EC 3.4.24.36). Here, the molecular dynamics simulation of Leishmania major GP63 in water at pH 7 is reported. Upon solvation, GP63 undergoes a sharp structural relaxation with respect to the crystal structure. The fluctuation pattern occurs essentially in solvent-exposed nonstructured regions. By contrast, the active site turns out to be rigid. Essential dynamics and dynamic-domain analyses, both carried out on the equilibrated portion of GP63, show that the fingerprint fluctuations of GP63 are practically characterized by the motion of a large part of the N-terminal domain. These results appear to be in line with substrate recognition and (pro)enzyme activation played by the N-terminal domain of GP63. A systematic analysis among a series of 10 homologs of GP63 also shows that the residues involved in the interdomain bending result highly conserved. This finding also suggests possible relationship between the maintainance of proteolytic activity and the similarity of the dynamical properties of the related enzymes.

Structural insight into the stereoselective inhibition of MMP-8 by enantiomeric sulfonamide phosphonates.

Potent and selective inhibitors of matrix metalloproteinases (MMPs), a family of zinc proteases that can degrade all the components of the extracellular matrix, could be useful for treatment of diseases such as cancer and arthritis. The most potent MMP inhibitors are based on hydroxamate as zinc-binding group (ZBG). alpha-Arylsulfonylamino phosphonates incorporate a particularly favorable combination of phosphonate as ZBG and arylsulfonylamino backbone so that their affinity exceptionally attains the nanomolar strength frequently observed for hydroxamate analogues. The detailed mode of binding of [1-(4'-methoxybiphenyl-4-sulfonylamino)-2-methylpropyl]phosphonate has been clarified by the crystal structures of the complexes that the R- and S-enantiomers respectively form with MMP-8. The reasons for the preferential MMP-8 inhibition by the R-phosphonate are underlined and the differences in the mode of binding of analogous alpha-arylsulfonylamino hydroxamates and carboxylates are discussed.

Synthesis and evaluation of new tripeptide phosphonate inhibitors of MMP-8 and MMP-2.

The phosphotryptophan derivative l-Pro-l-Leu-l-(P)Trp(OH)(2) (2b) was reported as the first example of left-hand-sideLeft-hand-side inhibitors: inhibitors that bind in the unprime region of the enzyme active site, in reference to the convention of drawing the unprimed residues of a peptide substrate on the left side. [R.P. Beckett et al., Drug Discov. Today 1 (1996) 16-26]. The opposite applies to right-hand-side inhibitors. phosphonate inhibitor of MMP-8. Its uncommon mode of binding to MMP-8 was mainly ascribed to the presence of the proline residue in P(3). Ten new analogues of 2b were obtained by replacement of the aminoterminal l-Pro with aminoacid residues bearing small side chains. Most of the new analogues show an increase of affinity for MMP-2 and MMP-8, and different profiles of selectivity. Computer simulations were performed to explain the effects of substitutions on the preferred mode of binding. They reveal that most of the new analogues are probably accommodated in the right, rather than left-hand side of MMP-8 active site.

Overexpression system and biochemical profile of CTX-M-3 extended-spectrum beta-lactamase expressed in Escherichia coli.

An efficient over-expression system was developed for CTX-M-3 extended-spectrum-beta-lactamase. The recombinant enzyme was purified from 1 l of culture to yield 22 mg of pure enzyme. The N-terminal amino acid sequence was determined to be NH2-QTADVQ... Determination of kinetic parameters with the purified CTX-M-3 revealed efficient hydrolysis of penicillins and cephalosporins, while ceftazidime and aztreonam were very poor substrates. Clavulanic acid, sulbactam and especially tazobactam inhibited the CTX-M-3 enzyme.

Structural insight into peroxisome proliferator-activated receptor gamma binding of two ureidofibrate-like enantiomers by molecular dynamics, cofactor interaction analysis, and site-directed mutagenesis.

Molecular dynamics simulations were performed on two ureidofibrate-like enantiomers to gain insight into their different potency and efficacy against PPARgamma. The partial agonism of the S enantiomer seems to be due to its capability to stabilize different regions of the receptor allowing the interaction with both coactivators and corepressors as shown by fluorescence resonance energy transfer (FRET) assays. The recruitment of the corepressor N-CoR1 by the S enantiomer on two different responsive elements of PPARgamma regulated promoters was confirmed by chromatin immunoprecipitation assays. Cell-based transcription assays show that PPARgamma coactivator 1alpha (PGC-1alpha) and cAMP response element binding protein-binding protein (CBP) enhance the basal and ligand-stimulated receptor activity acting as coactivators of PPARgamma, whereas the receptor interacting protein 140 (RIP140) and the nuclear corepressor 1 (N-CoR1) repress the transcriptional activity of PPARgamma. We also tested the importance of the residue Q286 on the transcriptional activity of the receptor by site-directed mutagenesis and confirmed its key role in the stabilization of helix 12. Molecular modeling studies were performed to provide a molecular explanation for the different behavior of the mutants.

Extra binding region induced by non-zinc chelating inhibitors into the S1' subsite of matrix metalloproteinase 8 (MMP-8).

The mode of binding and the activity of the first two non-zinc chelating, potent, and selective inhibitors of human neutrophil collagenase are reported. The crystal structures of the catalytic domain of MMP-8, respectively complexed with each inhibitor, reveals that both ligands are deeply inserted into the primary specificity subsite S(1)', where they induce a similar conformational change of the surrounding loop that is endowed with the main specificity determinants of MMPs. Accord to this rearrangement, both inhibitors remove the floor of the pocket formed by the Y227 side-chain, rendering available an extra binding region never explored before. The present data show that potent and more selective inhibitors can be obtained by developing ligands able to interact with the selectivity regions of the enzyme rather than with the catalytic zinc ion, which is the common feature of all MMP members.

New 2-aryloxy-3-phenyl-propanoic acids as peroxisome proliferator-activated receptors alpha/gamma dual agonists with improved potency and reduced adverse effects on skeletal muscle function.

The preparation of a new series of 2-aryloxy-3-phenyl-propanoic acids, resulting from the introduction of a linker into the diphenyl system of the previously reported PPARalpha/gamma dual agonist 1, allowed the identification of new ligands with improved potency on PPARalpha and unchanged activity on PPARgamma. For the most interesting stereoisomers S-2 and S-4, X-ray studies in PPARgamma and docking experiments in PPARalpha provided a molecular explanation for their different behavior as full and partial agonists of PPARalpha and PPARgamma, respectively. Due to the adverse effects provoked by hypolipidemic drugs on skeletal muscle function, we also investigated the blocking activity of S-2 and S-4 on skeletal muscle membrane chloride channel conductance and found that these ligands have a pharmacological profile more beneficial compared to fibrates currently used in therapy.

Crystal structure of the peroxisome proliferator-activated receptor gamma (PPARgamma) ligand binding domain complexed with a novel partial agonist: a new region of the hydrophobic pocket could be exploited for drug design.

The peroxisome proliferator-activated receptors (PPARs) are ligand-dependent transcription factors regulating glucose and lipid metabolism. The search for new PPAR ligands with reduced adverse effects with respect to the marketed antidiabetic agents thiazolidinediones (TZDs) and the dual-agonists glitazars is highly desired. We report the crystal structure and activity of the two enantiomeric forms of a clofibric acid analogue, respectively complexed with the ligand-binding domain (LBD) of PPARgamma, and provide an explanation on a molecular basis for their different potency and efficacy against PPARgamma. The more potent S-enantiomer is a dual PPARalpha/PPARgamma agonist which presents a partial agonism profile against PPARgamma. Docking of the S-enantiomer in the PPARalpha-LBD has been performed to explain its different subtype pharmacological profile. The hypothesis that partial agonists show differential stabilization of helix 3, when compared to full agonists, is also discussed. Moreover, the structure of the complex with the S-enantiomer reveals a new region of the PPARgamma-LBD never sampled before by other ligands.

alpha-Biphenylsulfonylamino 2-methylpropyl phosphonates: enantioselective synthesis and selective inhibition of MMPs.

(R)-alpha-Biphenylsulfonylamino 2-methylpropyl phosphonates attain nM potency against several MMPs and are the most effective inhibitors based on phosphonate as zinc binding group. Since their preparation by direct N-acylation of expensive, enantiopure, alpha-aminophosphonic acids proceeds in low yields, we devised and evaluated a stereoselective and straightforward method of synthesis that avoids the unfavourable step of N-acylation. The key intermediate (R)-4-bromophenylsulfonylamino 2-methylpropyl phosphonate 9 was obtained by highly stereoselective addition of dibenzylphosphite to the enantiopure (S)-N-isobutylidene-p-bromobenzenesulfinamide 3, followed by oxidation with m-CPBA. Suzuki coupling of 9 with the desired arylboronic acids, gave the expected biphenylsulfonylamino derivatives in satisfactory yields. Liberation of the phosphonic group by hydrogenolysis led to the desired (R)-alpha-biphenylsulfonylamino 2-methylpropyl phosphonates 14a-i. Screening of the new compounds on MMP-1, -2, -3, -7, -8, -9, -13 and -14 showed IC(50) in the range of nM in most cases.

Insights into the mechanism of partial agonism: crystal structures of the peroxisome proliferator-activated receptor gamma ligand-binding domain in the complex with two enantiomeric ligands.

The peroxisome proliferator-activated receptors (PPARs) are transcriptional regulators of glucose and lipid metabolism. They are activated by natural ligands, such as fatty acids, and are also targets of synthetic antidiabetic and hypolipidemic drugs. By using cell-based reporter assays, we studied the transactivation activity of two enantiomeric ureidofibrate-like derivatives. In particular, we show that the R-enantiomer, (R)-1, is a full agonist of PPARgamma, whereas the S-enantiomer, (S)-1, is a less potent partial agonist. Most importantly, we report the x-ray crystal structures of the PPARgamma ligand binding domain complexed with the R- and the S-enantiomer, respectively. The analysis of the two crystal structures shows that the different degree of stabilization of the helix 12 induced by the ligand determines its behavior as full or partial agonist. Another crystal structure of the PPARgamma.(S)-1 complex, only differing in the soaking time of the ligand, is also presented. The comparison of the two structures of the complexes with the partial agonist reveals significant differences and is suggestive of the possible coexistence in solution of transcriptionally active and inactive forms of helix 12 in the presence of a partial agonist. Mutation analysis confirms the importance of Leu(465), Leu(469), and Ile(472) in the activation by (R)-1 and underscores the key role of Gln(286) in the PPARgamma activity.

N-Hydroxyurea as zinc binding group in matrix metalloproteinase inhibition: mode of binding in a complex with MMP-8.

The first crystallographic structure of an N-hydroxyurea inhibitor bound into the active site of a matrix metalloproteinase is reported. The ligand and three other analogues were prepared and studied as inhibitors of MMP-2, MMP-3, and MMP-8. The crystal structure of the complex with MMP-8 shows that the N-hydroxyurea, contrary to the analogous hydroxamate, binds the catalytic zinc ion in a monodentate rather than bidentate mode and with high out-of-plane distortion of the amide bonds.

Dynamical aspects of TEM-1 beta-lactamase probed by molecular dynamics.

The dynamical aspects of the fully hydrated TEM-1 beta-lactamase have been determined by a 5 ns Molecular Dynamics simulation. Starting from the crystallographic coordinates, the protein shows a relaxation in water with an overall root mean square deviation from the crystal structure increasing up to 0.17 nm, within the first nanosecond. Then a plateau is reached and the molecule fluctuates around an equilibrium conformation. The results obtained in the first nanosecond are in agreement with those of a previous simulation (Diaz et al., J. Am. Chem. Soc., (2003) 125, 672-684). The successive equilibrium conformation in solution shows an increased mobility characterized by the following aspects. A flap-like translational motion anchors the omega-loop to the body of the enzyme. A relevant part of the backbone dynamics implies a rotational motion of one domain relative to the other. The water molecules in the active site can exchange with different residence times. The H-bonding networks formed by the catalytic residues are frequently interrupted by water molecules that could favour proton transfer reactions. An additional simulation, where the aspartyl dyad D214-D233 was considered fully deprotonated, shows that the active site is destabilized.

Design, modelling, synthesis and biological evaluation of peptidomimetic phosphinates as inhibitors of matrix metalloproteinases MMP-2 and MMP-8.

Three novel peptidomimetic phosphinate inhibitors have been synthesized and evaluated as inhibitors of matrix metalloproteinases MMP-2 and MMP-8. Their IC50 values are in the micromolar range, and one of them showed to be the most effective inhibitor of MMP-2. The differences in binding affinities for MMP-2 and MMP-8 of the three phosphinates have been rationalized by means of modelling studies and molecular dynamics simulations.

Peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt): conformation of Boc-Adt-Adt-NHMe and NH...S interactions.

To study the conformational preferences induced by the insertion of the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) residue into a peptide backbone, the achiral N-protected dipeptide methylamide Boc-Adt-Adt-NHMe (1) was synthesized and its crystal state and solution conformation studied and compared with that exhibited by its carba-analogue Boc-Ac5c-Ac5c-NHMe containing two residues of 1-aminocyclopentane-1-carboxylic acid (Ac5c). Compound 1 in the crystal adopts a type-III beta-turn conformation and an analogous structure is that preferred in chloroform solution as established by 1H-NMR and NOE information. In the crystal packing three different Adt rings form a cavity and the involved sulphur atoms give rise to unusual multiple interactions with one NH group. The chemical nature of these intermolecular and intramolecular main-chain...side-chain NH...S interactions are discussed in terms of quantum chemical calculations.

Exploring the interest of 1,2-dithiolane ring system in peptide chemistry. Synthesis of a chemotactic tripeptide and x-ray crystal structure of a 4-amino-1,2-dithiolane-4-carboxylic acid derivative.

Due to their relevant biological functions and specific chemical reactivity 1,2-dithiolanes (five-membered cyclic disulfides) represent an emerging class of heterocyclic compounds. However, despite the extensive research centered on lipoic acid and its analogues, only very few data are at the present available on peptides containing this ring system. We report here synthesis, conformation and bioactivity of a fMLF-OMe analogue, namely For-Met-Adt-Phe-OMe (7), in which the residue of the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) (4) replaces the central L-leucine. The crystal conformation of the synthetic intermediate Boc-Adt-OMe (5) is also described and compared to that of lipoic acid (R-1,2-dithiolane-3-pentanoic acid) (3) and asparagusic acid (1,2-dithiolane-4-carboxylic acid) (2).

Peptide backbone folding induced by the C(alpha)-tetrasubstituted cyclic alpha-amino acids 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) and 1-aminocyclopentane-1-carboxylic acid (Ac5c). A joint computational and experimental study.

The conformational study of a new group of synthetic peptides containing 4-amino-1,2-dithiolane-4-carboxylic acid (Adt), a cysteine-related achiral residue, has been carried out through a joint application of computational and experimental methodologies. Molecular Dynamics simulations clearly suggest the tendency of this molecule to adopt a gamma-turn conformation in vacuum and help in analyzing the complex and crucial conformational behaviour of the dithiolane ring which appears to preferentially adopt a C(S)-like structure. Electronic structure calculations carried out in solution using the Density Functional Theory also indicate the preservation of the gamma-like folding in apolar solvents and the helix-like one in more polar solvents. A comparison with the achiral 1-aminocycloalkane-1-carboxylic acid (Ac5c) has been carried out using the same computational tools. NMR and IR data on dipeptide derivatives containing the Adt or Ac5c residue show that in chloroform solution all the models prefer a gamma-turn structure, centered at the cyclic residue, stabilized by an intramolecular H-bond, whereas in a more polar solvent, i.e. dimethyl sulfoxide, this folding is not maintained. The experimental conformational studies, extended to N-Boc protected tripeptides, clearly indicate the remarkable tendency of both the five-membered C(alpha)-tetrasubstituted cyclic amino acids Adt and Ac5c to induce the gamma-turn structure also in models able to adopt the beta-bend conformation.