Metal-coordinating Motif Research Articles

Rheological Properties of Ionically Crosslinked Viscoelastic 2D Films vs. Corresponding 3D Bulk Hydrogels.

Ionically crosslinked hydrogels containing metal coordination motifs have piqued the interest of researchers in recent decades due to their self-healing and adhesive properties. In particular, catechol-functionalized bulk hydrogels have received a lot of attention because of their bioinspired nature. By contrast, very little is known about thin viscoelastic membranes made using similar chelator-ion pair motifs. This shortcoming is surprising because the unique interfacial properties of these membranes, namely, their self-healing and adhesion, would be ideal for capsule shells, adhesives, or for drug delivery purposes. We recently demonstrated the feasibility to fabricate 10 nm thick viscoelastic membranes from catechol-functionalized surfactants that are ionically crosslinked at the liquid/liquid interface. However, it is unclear if the vast know-how existing on the influence of the chelator-ion pair on the mechanical properties of ionically crosslinked three-dimensional (3D) hydrogels can be translated to two-dimensional (2D) systems. To address this question, we compare the dynamic mechanical properties of ionically crosslinked pyrogallol functionalized hydrogels with those of viscoelastic membranes that are crosslinked using the same chelator-ion pairs. We demonstrate that the storage and loss moduli of viscoelastic membranes follow a trend similar to that of the hydrogels, with the membrane becoming stronger as the ion-chelator affinity increases. Yet, membranes relax significantly faster than bulk equivalents. These insights enable the targeted design of viscoelastic, adhesive, self-healing membranes possessing tunable mechanical properties. Such capsules can potentially be used, for example, in cosmetics, as granular inks, or with additional work that includes replacing the fluorinated block by a hydrocarbon-based one in drug delivery and food applications.

Capturing the geometry, function, and evolution of enzymes with 3D templates.

Structural templates are 3D signatures representing protein functional sites, such as ligand binding cavities, metal coordination motifs, or catalytic sites. Here we explore methods to generate template libraries and algorithms to query structures for conserved 3D motifs. Applications of templates are discussed, as well as some exemplar cases for examining evolutionary links in enzymes. We also introduce the concept of using more than one template per structure to represent flexible sites, as an approach to better understand catalysis through snapshots captured in enzyme structures. Functional annotation from structure is an important topic that has recently resurfaced due to the new more accurate methods of protein structure prediction. Therefore, we anticipate that template‐based functional site detection will be a powerful tool in the task of characterizing a vast number of new protein models.

Structural Basis for Rare Earth Element Recognition by Methylobacterium extorquens Lanmodulin.

Lanmodulin (LanM) is a high-affinity lanthanide (Ln)-binding protein recently identified in Methylobacterium extorquens, a bacterium that requires Lns for the function of at least two enzymes. LanM possesses four EF-hands, metal coordination motifs generally associated with CaII binding, but it undergoes a metal-dependent conformational change with a 100 million-fold selectivity for LnIIIs and YIII over CaII. Here we present the nuclear magnetic resonance solution structure of LanM complexed with YIII. This structure reveals that LanM features an unusual fusion of adjacent EF-hands, resulting in a compact fold to the best of our knowledge unique among EF-hand-containing proteins. It also supports the importance of an additional carboxylate ligand in contributing to the protein's picomolar affinity for LnIIIs, and it suggests a role of unusual N i+1-H···N i hydrogen bonds, in which LanM's unique EF-hand proline residues are engaged, in selective LnIII recognition. This work sets the stage for a detailed mechanistic understanding of LanM's Ln selectivity, which may inspire new strategies for binding, detecting, and sequestering these technologically important metals.

Driving Protein Conformational Changes with Light: Photoinduced Structural Rearrangement in a Heterobimetallic Oxidase.

The heterobimetallic R2lox protein binds both manganese and iron ions in a site-selective fashion and activates oxygen, ultimately performing C-H bond oxidation to generate a tyrosine-valine cross-link near the active site. In this work, we demonstrate that, following assembly, R2lox undergoes photoinduced changes to the active site geometry and metal coordination motif. Through spectroscopic, structural, and mass spectrometric characterization, the photoconverted species is found to consist of a tyrosinate-bound iron center following light-induced decarboxylation of a coordinating glutamate residue and cleavage of the tyrosine-valine cross-link. This process occurs with high quantum efficiencies (Φ = 3%) using violet and near-ultraviolet light, suggesting that the photodecarboxylation is initiated via ligand-to-metal charge transfer excitation. Site-directed mutagenesis and structural analysis suggest that the cross-linked tyrosine-162 is the coordinating residue. One primary product is observed following irradiation, indicating potential use of this class of proteins, which contains a putative substrate channel, for controlled photoinduced decarboxylation processes, with relevance for in vivo functionality of R2lox as well as application in environmental remediation.

Tunable Helicity, Stability and DNA-Binding Properties of Short Peptides with Hybrid Metal Coordination Motifs.

Given the prevalent role of α-helical motifs on protein surfaces in mediating protein-protein and protein-DNA interactions, there have been significant efforts to develop strategies to induce α-helicity in short, unstructured peptides to interrogate such interactions. Toward this goal, we have recently introduced hybrid metal coordination motifs (HCMs). HCMs combine a natural metal-binding amino acid side chain with a synthetic chelating group that are appropriately positioned in a peptide sequence to stabilize an α-helical conformation upon metal coordination. Here, we present a series of short peptides modified with HCMs consisting of a His and a phenanthroline group at i and i+7 positions that can induce α-helicity in a metal-tunable fashion as well as direct the formation of discrete dimeric architectures for recognition of biological targets. We show that the induction of α-helicity can be further modulated by secondary sphere interactions between amino acids at the i+4 position and the HCM. A frequently cited drawback of the use of peptides as therapeutics is their propensity to be quickly digested by proteases; here, we observe an enhancement of up to ∼100-fold in the half-lifes of the metal-bound HCM-peptides in the presence of trypsin. Finally, we show that an HCM-bearing peptide sequence, which contains the DNA-recognition domain of a bZIP protein but is devoid of the obligate dimerization domain, can dimerize with the proper geometry and in an α-helical conformation to bind a cognate DNA sequence with high affinities (Kd≥ 65 nM), again in a metal-tunable manner.

Bioinspired Reversibly Cross‐linked Hydrogels Comprising Polypeptide Micelles Exhibit Enhanced Mechanical Properties

Noncovalently cross‐linked networks are attractive hydrogel platforms because of their facile fabrication, dynamic behavior, and biocompatibility. The majority of noncovalently cross‐linked hydrogels, however, exhibits poor mechanical properties, which significantly limit their utility in load bearing applications. To address this limitation, hydrogels are presented composed of micelles created from genetically engineered, amphiphilic, elastin‐like polypeptides that contain a relatively large hydrophobic block and a hydrophilic terminus that can be cross‐linked through metal ion coordination. To create the hydrogels, heat is firstly used to trigger the self‐assembly of the polypeptides into monodisperse micelles that display transition metal coordination motifs on their coronae, and subsequently cross‐link the micelles by adding zinc ions. These hydrogels exhibit hierarchical structure, are stable over a large temperature range, and exhibit tunable stiffness, self‐healing, and fatigue resistance. Gels with polypeptide concentration of 10%, w/v, and higher show storage moduli of ≈1 MPa from frequency sweep tests and exhibit self‐healing within minutes. These reversibly cross‐linked, hierarchical hydrogels with enhanced mechanical properties have potential utility in a variety of biomedical applications.

Supramolecular patterns of cationic and neutral Ni(ii) complexes from the interplay of hydrogen-bonding, stacking interactions and metal-coordination motifs

In an effort to explore the way in which the chemical subunits of crystal structures of transition metal complexes are put together in periodic ordered arrays in the solid state via noncovalent interactions, an investigation on a series of 13 nickel(II) complexes has been carried out. The complexes were isolated from the general NiII/X−/L or HL′ [X− = Cl−, Br−, I−, NO3−, NO2−, ClO4−; L = 1-methyl-4,5-diphenylimidazole, and HL′ = 4,5-diphenylimidazole] reaction system. A single-crystal diffraction analysis shows that, independently of the ligand used, most of the complexes contain the rigid square planar [NiL4]2+ (1–5) or [Ni(HL′)4]2+ (6–10) cation, which seems to have an impact on the self-assembly process by adopting a structure-directing role: the supramolecular assembly is organized around the rigid bulky cations via interactions with the surrounding counterion/solvent clusters in each individual structure. The components of the clusters, i.e. OH−/H2O (1), [NiCl4]2–/EtOH (2), Br−/H2O (3), NO3−/MeOH (4), ClO4−/Me2CO (5), Cl−/H2O (6), Br−/MeCN (7), I−/Me2CO/H2O (8), NO3−/EtOH/H2O (9), and ClO4−/Me2CO (10), are held tightly together by strong or weak hydrogen bonding. The structure-directing action of the cations is accomplished via weak C–H⋯O/Cl/Br−, π⋯π and C–H⋯π interactions (for L-containing complexes) or strong recurring N–H⋯/Cl−/Br−/I−/O motifs dominating the molecular self-assembly together with weak interactions (for HL′-containing complexes). The variety of the stereochemistries observed among the studied compounds (square planar, 1–10; tetrahedral, 11 and 12; octahedral, 13) seems to advocate the choice of nickel as an interesting candidate in metallosupramolecular research.

The Putative Metal Coordination Motif in the Endonuclease Domain of Human Parvovirus B19 NS1 Is Critical for NS1 Induced S Phase Arrest and DNA Damage

The non-structural proteins (NS) of the parvovirus family are highly conserved multi-functional molecules that have been extensively characterized and shown to be integral to viral replication. Along with NTP-dependent helicase activity, these proteins carry within their sequences domains that allow them to bind DNA and act as nucleases in order to resolve the concatameric intermediates developed during viral replication. The parvovirus B19 NS1 protein contains sequence domains highly similar to those previously implicated in the above-described functions of NS proteins from adeno-associated virus (AAV), minute virus of mice (MVM) and other non-human parvoviruses. Previous studies have shown that transient transfection of B19 NS1 into human liver carcinoma (HepG2) cells initiates the intrinsic apoptotic cascade, ultimately resulting in cell death. In an effort to elucidate the mechanism of mammalian cell demise in the presence of B19 NS1, we undertook a mutagenesis analysis of the protein's endonuclease domain. Our studies have shown that, unlike wild-type NS1, which induces an accumulation of DNA damage, S phase arrest and apoptosis in HepG2 cells, disruptions in the metal coordination motif of the B19 NS1 protein reduce its ability to induce DNA damage and to trigger S phase arrest and subsequent apoptosis. These studies support our hypothesis that, in the absence of replicating B19 genomes, NS1-induced host cell DNA damage is responsible for apoptotic cell death observed in parvoviral infection of non-permissive mammalian cells.

Multiresponsive Reversible Polymer Networks Based on Hydrogen Bonding and Metal Coordination

Side-chain-functionalized polymers containing hydrogen bonding and metal coordination sites have been synthesized using ring-opening metathesis polymerization. These polymers were cross-linked reversibly either selectively by using hydrogen bonding or metal coordination or simultaneously using both interactions through the addition of small molecule cross-linking agents. The hydrogen bonding motifs utilized for reversible cross-linking are based on cyanuric acid residues hydrogen bonded to 2,4-diaminotriazine-based cross-linking agents. The metal coordination motifs are based on palladated SCS pincer complexes coordinated to bispyridine cross-linking agents. By controlling the reversible cross-linking strategy, we were able to modulate (1) the rheology of the polymer networks from a free-flowing liquid to a highly elastic gel and vice versa and vary the dynamic moduli over 10 orders of magnitude and (2) the responsiveness of the networks to external stimuli such as temperature and ligand displacement agents. The hydrogen bonded cross-linking resulted in polymer networks that were thermally reversible whereas the metal coordinated cross-linked networks mainly showed chemoresponsive behavior. Since both interactions are fully orthogonal to each other, we successfully cross-linked the polymer using both interactions to obtain multiresponsive networks that exhibited both thermal and chemoresponsiveness. We were also able to selectively de-cross-link the hydrogen bonded cross-links of the multifunctionalized networks through competitive interactions at room temperature via the addition of a monotopic end-capping agent without affecting the metal coordinated cross-links. In contrast, the metal coordination could be de-cross-linked completely using a ligand displacement agent such as triphenylphosphine again without affecting the hydrogen bonded cross-links.

Deciphering the Distinct Role for the Metal Coordination Motif in the Catalytic Activity of Mycobacterium smegmatis Topoisomerase I

Mycobacterium smegmatis topoisomerase I (MstopoI) is distinct from typical type IA topoisomerases. The enzyme binds to both single- and double-stranded DNA with high affinity, making specific contacts. The enzyme comprises conserved regions similar to type IA topoisomerases from Escherichia coli and other eubacteria but lacks the typically found zinc fingers in the carboxy-terminal domain. The enzyme can perform DNA cleavage in the absence of Mg2+, but religation needs exogenously added Mg2+. One molecule of Mg2+ tightly bound to the enzyme has no role in DNA cleavage but is needed only for the religation reaction. The toprim (topoisomerase–primase) domain in MstopoI comprising the Mg2+ binding pocket, conserved in both type IA and type II topoisomerases, was subjected to mutagenesis to understand the role of Mg2+ in different steps of the reaction. The residues D108, D110, and E112 of the enzyme, which form the acidic triad in the DXDXE motif, were changed to alanines. D108A mutation resulted in an enzyme that is Mg2+ dependent for DNA cleavage unlike MstopoI and exhibited enhanced DNA cleavage property and reduced religation activity. The mutant was toxic for cell growth, most likely due to the imbalance in cleavage–religation equilibrium. In contrast, the E112A mutant behaved like wild-type enzyme, cleaving DNA in a Mg2+-independent fashion, albeit to a reduced extent. Intra- and intermolecular religation assays indicated specific roles for D108 and E112 residues during the reaction. Together, these results indicate that the D108 residue has a major role during cleavage and religation, while E112 is important for enhancing the efficiency of cleavage. Thus, although architecturally and mechanistically similar to topoisomerase I from E. coli, the metal coordination pattern of the mycobacterial enzyme is distinct, opening up avenues to exploit the enzyme to develop inhibitors.

Two Roads Diverged: The Structure of Hydroxymandelate Synthase from Amycolatopsis orientalis in Complex with 4-Hydroxymandelate,

The crystal structure of the hydroxymandelate synthase (HMS).Co2+.hydroxymandelate (HMA) complex determined to a resolution of 2.3 A reveals an overall fold that consists of two similar beta-barrel domains, one of which contains the characteristic His/His/acid metal-coordination motif (facial triad) found in the majority of Fe2+-dependent oxygenases. The fold of the alpha-carbon backbone closely resembles that of the evolutionarily related enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) in its closed conformation with a root-mean-square deviation of 1.85 A. HPPD uses the same substrates as HMS but forms instead homogentisate (HG). The active site of HMS is significantly smaller than that observed in HPPD, reflecting the relative changes in shape that occur in the conversion of the common HPP substrate to the respective HMA or HG products. The HMA benzylic hydroxyl and carboxylate oxygens coordinate to the Co2+ ion, and three other potential H-bonding interactions to active site residue side chains are observed. Additionally, it is noted that there is a buried well-ordered water molecule 3.2 A from the distal carboxylate oxygen. The p-hydroxyl group of HMA is within hydrogen-bonding distance of the side chain hydroxyl of a serine residue (Ser201) that is conserved in both HMS and HPPD. This potential hydrogen bond and the known geometry of iron ligation for the substrate allowed us to model 4-hydroxyphenylpyruvate (HPP) in the active sites of both HMS and HPPD. These models suggest that the position of the HPP substrate differs between the two enzymes. In HMS, HPP binds analogously to HMA, while in HPPD, the p-hydroxyl group of HPP acts as a hydrogen-bond donor and acceptor to Ser201 and Asn216, respectively. It is suggested that this difference in the ring orientation of the substrate and the corresponding intermediates influences the site of hydroxylation.

Variations of the 2‐His‐1‐carboxylate Theme in Mononuclear Non‐Heme FeII Oxygenases

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Variations of the 2‐His‐1‐carboxylate Theme in Mononuclear Non‐Heme FeII Oxygenases

A facial triad of two histidine side chains and one aspartate or glutamate side chain forms the canonical metal-coordinating motif in the catalytic centers of various mononuclear non-heme Fe(II) enzymes. Although these active sites are based on totally unrelated protein folds and bring about a wide range of chemical transformations, most of them share the ability to couple dioxygen reduction with the oxygenation of an organic substrate. With the increasing number of protein structures now solved, it has become clear that the 2-His-1-carboxylate signature is less of a paradigm for non-heme Fe(II) active sites than had long been thought and that it can be replaced by alternative metal centers in various oxygenases, the structure-function relationships and proposed catalytic mechanisms of which are reviewed here. Metal coordination through three histidines and one glutamate constitutes the classical motif described for enzyme members of the cupin protein superfamily, such as aci-reductone dioxygenase and quercetin dioxygenase, multiple metal forms of which (including the Fe(II) type) are found in nature. Cysteine dioxygenase and diketone dioxygenase, which are strictly Fe(II)-dependent oxygenases based on the cupin fold, bind the catalytic metal through the homologous triad of histidines, but lack the fourth glutamate ligand. An alpha-ketoglutarate-dependent Fe(II) halogenase shows metal coordination by two histidines as the only protein-derived ligands, whilst carotene oxygenase, from a different protein fold family, features an Fe(II) site consisting of four histidine side chains. These recently discovered metallocenters are discussed with respect to their metal-binding properties and the reaction coordinates of the O(2)-dependent conversions they catalyze.

The interplay of hydrogen-bonding and metal-coordination motifs in the formation of supramolecular patterns: Copper/zinc malonates–aminopyrimidine complexes

The X-ray crystal structures of 1 [2[AMPYH] · [(Cu (H 2O) (mal) 2)]:2H 2O] and 2 [2[AMPYH] · [ZnBr (Hmal) (mal)]:2H 2O ] [mal = malonate; Hmal = hydrogen malonate; AMPYH = 2-amino-4, 6-dimethylpyrimidinium] reveal the interplay of metal-coordination motifs and the hydrogen-bonding patterns . In both the structures, the 2-amino-4,6-dimethylpyrimidine cations are not directly coordinated to copper and zinc, but are hydrogen-bonded to the malonate ion. The protonated endocyclic nitrogen and the amino group of 2-amino-4,6-dimethylpyrimidine molecule interact with malonate ligand via a pair of N–H⋯O hydrogen-bonds, (with graph set notation R 2 2 ( 8 ) ) whereas the unprotonated endocyclic nitrogen and the amino group interact with the malonate ligand via N–H..O and C–H⋯N hydrogen-bonds forming the same R 2 2 ( 8 ) motif. The combination of hydrogen-bonding motif and metal-coordination motif creates a novel supramolecular motif. The interplay of the hydrogen-bonding motif and metal-coordination motif via hydrogen-bonds leads to similar supramolecular motifs in both the structures.

Molecular and Functional Differences between Heart mKv1.7 Channel Isoforms

Ion channels are membrane-spanning proteins that allow ions to permeate at high rates. The kinetic characteristics of the channels present in a cell determine the cell signaling profile and therefore cell function in many different physiological processes. We found that Kv1.7 channels from mouse heart muscle have two putative translation initiation start sites that generate two channel isoforms with different functional characteristics, mKv1.7L (489 aa) and a shorter mKv1.7S (457 aa). The electrophysiological analysis of mKv1.7L and mKv1.7S channels revealed that the two channel isoforms have different inactivation kinetics. The channel resulting from the longer protein (L) inactivates faster than the shorter channels (S). Our data supports the hypothesis that mKv1.7L channels inactivate predominantly due to an N-type related mechanism, which is impaired in the mKv1.7S form. Furthermore, only the longer version mKv1.7L is regulated by the cell redox state, whereas the shorter form mKv1.7S is not. Thus, expression starting at each translation initiation site results in significant functional divergence. Our data suggest that the redox modulation of mKv1.7L may occur through a site in the cytoplasmic N-terminal domain that seems to encompass a metal coordination motif resembling those found in many redox-sensitive proteins. The mRNA expression profile and redox modulation of mKv1.7 kinetics identify these channels as molecular entities of potential importance in cellular redox-stress states such as hypoxia.

Evolutionary connection between the catalytic subunits of DNA-dependent RNA polymerases and eukaryotic RNA-dependent RNA polymerases and the origin of RNA polymerases

BackgroundThe eukaryotic RNA-dependent RNA polymerase (RDRP) is involved in the amplification of regulatory microRNAs during post-transcriptional gene silencing. This enzyme is highly conserved in most eukaryotes but is missing in archaea and bacteria. No evolutionary relationship between RDRP and other polymerases has been reported so far, hence the origin of this eukaryote-specific polymerase remains a mystery.ResultsUsing extensive sequence profile searches, we identified bacteriophage homologs of the eukaryotic RDRP. The comparison of the eukaryotic RDRP and their homologs from bacteriophages led to the delineation of the conserved portion of these enzymes, which is predicted to harbor the catalytic site. Further, detailed sequence comparison, aided by examination of the crystal structure of the DNA-dependent RNA polymerase (DDRP), showed that the RDRP and the β' subunit of DDRP (and its orthologs in archaea and eukaryotes) contain a conserved double-psi β-barrel (DPBB) domain. This DPBB domain contains the signature motif DbDGD (b is a bulky residue), which is conserved in all RDRPs and DDRPs and contributes to catalysis via a coordinated divalent cation. Apart from the DPBB domain, no similarity was detected between RDRP and DDRP, which leaves open two scenarios for the origin of RDRP: i) RDRP evolved at the onset of the evolution of eukaryotes via a duplication of the DDRP β' subunit followed by dramatic divergence that obliterated the sequence similarity outside the core catalytic domain and ii) the primordial RDRP, which consisted primarily of the DPBB domain, evolved from a common ancestor with the DDRP at a very early stage of evolution, during the RNA world era. The latter hypothesis implies that RDRP had been subsequently eliminated from cellular life forms and might have been reintroduced into the eukaryotic genomes through a bacteriophage. Sequence and structure analysis of the DDRP led to further insights into the evolution of RNA polymerases. In addition to the β' subunit, β subunit of DDRP also contains a DPBB domain, which is, however, distorted by large inserts and does not harbor a counterpart of the DbDGD motif. The DPBB domains of the two DDRP subunits together form the catalytic cleft, with the domain from the β' subunit supplying the metal-coordinating DbDGD motif and the one from the β subunit providing two lysine residues involved in catalysis. Given that the two DPBB domains of DDRP contribute completely different sets of active residues to the catalytic center, it is hypothesized that the ultimate ancestor of RNA polymerases functioned as a homodimer of a generic, RNA-binding DPBB domain. This ancestral protein probably did not have catalytic activity and served as a cofactor for a ribozyme RNA polymerase. Subsequent evolution of DDRP and RDRP involved accretion of distinct sets of additional domains. In the DDRPs, these included a RNA-binding Zn-ribbon, an AT-hook-like module and a sandwich-barrel hybrid motif (SBHM) domain. Further, lineage-specific accretion of SBHM domains and other, DDRP-specific domains is observed in bacterial DDRPs. In contrast, the orthologs of the β' subunit in archaea and eukaryotes contains a four-stranded α + β domain that is shared with the α-subunit of bacterial DDRP, eukaryotic DDRP subunit RBP11, translation factor eIF1 and type II topoisomerases. The additional domains of the RDRPs remain to be characterized.ConclusionsEukaryotic RNA-dependent RNA polymerases share the catalytic double-psi β-barrel domain, containing a signature metal-coordinating motif, with the universally conserved β' subunit of DNA-dependent RNA polymerases. Beyond this core catalytic domain, the two classes of RNA polymerases do not have common domains, suggesting early divergence from a common ancestor, with subsequent independent domain accretion. The β-subunit of DDRP contains another, highly diverged DPBB domain. The presence of two distinct DPBB domains in two subunits of DDRP is compatible with the hypothesis that the ultimate ancestor of RNA polymerases was a RNA-binding DPBB domain that had no catalytic activity but rather functioned as a homodimeric cofactor for a ribozyme polymerase.

Interlocking molecular grid lattices involving weak assembly forces

The X-ray structures of the two diquinoline derivatives 6,13-dihydro-6,13-ethano-5,12-diazapentacene (1) and 6α,13α-dibromo-2,9-dichloro-5bα,6,12bα,13-tetrahydropentaleno[1,2-b:4,5-b′]diquinoline (2) reveal that both crystallise by forming network lattices involving only weak intermolecular forces. These very similar lattices contain no aryl edge–edge C–H⋯N R22(8) dimers or efficient aryl offset face–face interactions, commonly found in related diquinoline crystals. Both lattices arise from multiple interlocking, at an inclined angle, of two identical sets of parallel molecular grids. Each grid connector site comprises a centrosymmetric tetramer of molecules held together by weak intermolecular forces, unlike the metal co-ordination motifs normally used to generate grid structures. Edge–edge C–H⋯N weak hydrogen bonds of various types help stabilise these structures by linking molecules of opposite handedness in neighbouring grids.