Structural studies on Δ3-Δ2-enoyl-CoA isomerase: the variable mode of assembly of the trimeric disks of the crotonase superfamily

AbstractSubunits of the enzymes in the crotonase superfamily form tight trimeric disks. In most members of this protein superfamily these disks assemble further into hexamers. Here we report on the 2.1 Å structure of a tight hexameric crystal form of the yeast peroxisomal Δ3-Δ2-enoyl-CoA isomerase (Eci1p). A comparison of this structure to a previously solved crystal form of Eci1p and other structures of this superfamily shows that there is much variability with respect to the relative distance between the disks and their relative orientations. In particular helices H2 and H9 are involved in the inter-trimer contacts and there are considerable structural differences in these helices in this superfamily. Helices H2 and H9 are near the catalytic cavity and it is postulated that the observed structural variability of these helices, stabilized by the different modes of assembly, has allowed the evolution of the wide range of substrate and catalytic specificity within this enzyme superfamily

Structure of transmembrane prolyl 4-hydroxylase reveals unique organization of EF and dioxygenase domains

Prolyl 4-hydroxylases (P4Hs) catalyze post-translational hydroxylation of peptidyl proline residues. In addition to collagen P4Hs and hypoxia-inducible factor P4Hs, a third P4H—the poorly characterized endoplasmic reticulum–localized transmembrane prolyl 4-hydroxylase (P4H-TM)—is found in animals. P4H-TM variants are associated with the familiar neurological HIDEA syndrome, but how these variants might contribute to disease is unknown. Here, we explored this question in a structural and functional analysis of soluble human P4H-TM. The crystal structure revealed an EF domain with two Ca2+-binding motifs inserted within the catalytic domain. A substrate-binding groove was formed between the EF domain and the conserved core of the catalytic domain. The proximity of the EF domain to the active site suggests that Ca2+ binding is relevant to the catalytic activity. Functional analysis demonstrated that Ca2+-binding affinity of P4H-TM is within the range of physiological Ca2+ concentration in the endoplasmic reticulum. P4H-TM was found both as a monomer and a dimer in the solution, but the monomer–dimer equilibrium was not regulated by Ca2+. The catalytic site contained bound Fe2+ and N-oxalylglycine, which is an analogue of the cosubstrate 2-oxoglutarate. Comparison with homologous P4H structures complexed with peptide substrates showed that the substrate-interacting residues and the lid structure that folds over the substrate are conserved in P4H-TM, whereas the extensive loop structures that surround the substrate-binding groove, generating a negative surface potential, are different. Analysis of the structure suggests that the HIDEA variants cause loss of P4H-TM function. In conclusion, P4H-TM shares key structural elements with other P4Hs while having a unique EF domain.publishedVersio

Complementary substrate specificity and distinct quaternary assembly of the Escherichia coli aerobic and anaerobic beta-oxidation trifunctional enzyme complexes

The trifunctional enzyme (TFE) catalyzes the last three steps of the fatty acid beta-oxidation cycle. Two TFEs are present in Escherichia coli, EcTFE and anEcTFE. EcTFE is expressed only under aerobic conditions, whereas anEcTFE is expressed also under anaerobic conditions, with nitrate or fumarate as the ultimate electron acceptor. The anEcTFE subunits have higher sequence identity with the human mitochondrial TFE (HsTFE) than with the soluble EcTFE. Like HsTFE, here it is found that anEcTFE is a membrane-bound complex. Systematic enzyme kinetic studies show that anEcTFE has a preference for medium- and long-chain enoyl-CoAs, similar to HsTFE, whereas EcTFE prefers short chain enoyl-CoA substrates. The biophysical characterization of anEcTFE and EcTFE shows that EcTFE is heterotetrameric, whereas anEcTFE is purified as a complex of two heterotetrameric units, like HsTFE. The tetrameric assembly of anEcTFE resembles the HsTFE tetramer, although the arrangement of the two anEcTFE tetramers in the octamer is different from the HsTFE octamer. These studies demonstrate that EcTFE and anEcTFE have complementary substrate specificities, allowing for complete degradation of long-chain enoyl-CoAs under aerobic conditions. The new data agree with the notion that anEcTFE and HsTFE are evolutionary closely related, whereas EcTFE belongs to a separate subfamily.Peer reviewe

Correction:How the COVID-19 pandemic highlights the necessity of animal research (vol 30, pg R1014, 2020)

(Current Biology 30, R1014–R1018; September 21, 2020) As a result of an author oversight in the originally published version of this article, a number of errors were introduced in the author list and affiliations. First, the middle initials were omitted from the names of several authors. Second, the surname of Dr. van Dam was mistakenly written as “Dam.” Third, the first name of author Bernhard Englitz was misspelled as “Bernard” and the surname of author B.J.A. Pollux was misspelled as “Pullox.” Finally, Dr. Keijer's first name was abbreviated rather than written in full. These errors, as well as various errors in the author affiliations, have now been corrected online

Enzymes of the crotonase superfamily:diverse assembly and diverse function

Abstract The crotonase fold is generated by a framework of four repeats of a ββα-unit, extended by two helical regions. The active site of crotonase superfamily (CS) enzymes is located at the N-terminal end of the helix of the third repeat, typically being covered by a C-terminal helix. A major subset of CS-enzymes catalyzes acyl-CoA-dependent reactions, allowing for a diverse range of acyl-tail modifications. Most of these enzymes occur as trimers or hexamers (dimers of trimers), but monomeric forms are also observed. A common feature of the active sites of CS-enzymes is an oxyanion hole, formed by two peptide-NH hydrogen bond donors, which stabilises the negatively charged thioester oxygen atom of the reaction intermediate. Structural properties and possible use of these enzymes for biotechnological applications are discussed

Prediction of the Occurrence of the ADP-binding βαβ-fold in Proteins, Using an Amino Acid Sequence Fingerprint

An amino acid sequence "fingerprint” has been derived that can be used to test if a particular sequence will fold into a βαβ-unit with ADP-binding properties. It was deduced from a careful analysis of the known three-dimensional structures of ADP-binding βαβ-folds. This fingerprint is in fact a set of 11 rules describing the type of amino acid that should occur at a specific position in a peptide fragment. The total length of this fingerprint varies between 29 and 31 residues. By checking against all possible sequences in a database, it appeared that every peptide, which exactly follows this fingerprint, does indeed fold into an ADP-binding βαβ-unit.

Structure of Mycobacterial β‑Oxidation Trifunctional Enzyme Reveals Its Altered Assembly and Putative Substrate Channeling Pathway

The incidence of tuberculosis is increasing due to the appearance of new drug-resistant variants. A thorough understanding of the disease organism is essential in order to create more effective drugs. In an attempt to understand better the poorly studied lipid metabolism of <i>Mycobacterium tuberculosis</i> (Mtb), we identified and characterized its fatty acid β-oxidation complex (trifunctional enzyme (TFE)). TFE is an α₂β₂ complex consisting of two types of polypeptides catalyzing three of the four reactions of the β-oxidation of fatty acids. The kinetic constants (<i>k</i>_cat and <i>K</i>_m) show that the complexed α chain is more active than the individual α chain. Crystal structures of Mtb TFE (mtTFE) reveal that the quaternary assembly is strikingly different from the already known <i>Pseudomonas fragi</i> TFE (pfTFE) assembly due to the presence of a helical insertion (LA5) in the mtTFE-β subunit. This helical insertion prevents the pfTFE mode of assembly, as it would clash with helix H9A of the TFE-α chain. The mtTFE assembly appears to be more rigid and results in a different substrate channeling path between the α and the β subunits. Structural comparisons suggest that the mtTFE active sites can accommodate bulkier fatty acyl chains than in pfTFE. Although another thiolase (FadA2), more closely related to human TFE-β/thiolase, is present in the Mtb genome, it does not form a complex with mtTFE-α. Extensive phylogenetic analyses show that there are at least four TFE subfamilies. Our studies highlight the molecular properties of mtTFE, significantly extending the structural knowledge on this type of very interesting multifunctional enzymes

The extended structure of the periplasmic region of CdsD, a structural protein of the type III secretion system of Chlamydia trachomatis

The type III secretion system (T3SS) is required for the virulence of many gram-negative bacterial human pathogens. It is composed of several structural proteins, forming the secretion needle and its basis, the basal body. In Chlamydia spp., the T3SS inner membrane ring (IM-ring) of the basal body is formed by the periplasmic part of CdsD (outer ring) and CdsJ (inner ring). Here we describe the crystal structure of the C-terminal, periplasmic part of CdsD, not including the last 60 residues. Two crystal forms were obtained, grown in three different crystallization conditions. In both crystal forms there is one molecule per asymmetric unit adopting a similar extended structure. The structures consist of three periplasmic domains (PDs) of similar αββαβ topology as seen also in the structures of the homologous PrgH (Salmonella typhimurium) and YscD (Yersinia enterocolitica). Only in the C2 crystal form, there is a C-terminal additional helix after the PD3 domain. The relative orientation of the three subsequent CdsD PD domains with respect to each other is more extended than in PrgH but less extended than in YscD. Small-angle X-ray scattering data show that also in solution this CdsD construct adopts the same elongated shape. In both crystal forms the CdsD molecules are packed in a parallel fashion, using translational crystallographic symmetry. The most extensive crystal contacts are preserved in both crystal forms, suggesting a possible mode of assembly of the CdsD periplasmic part into a 24-mer complex forming the outer ring of the IM-ring of the T3SS

The importance of the conserved Arg191-Asp227 salt bridge of triosephosphate isomerase for folding, stability, and catalysis

AbstractTriosephosphate isomerase (TIM) has a conserved salt bridge 20 Å away from both the active site and the dimer interface. In this study, four salt bridge mutants of Trypanosoma brucei brucei TIM were characterized. The folding and stability of the mutants are impaired compared to the wild-type enzyme. This salt bridge is part of a hydrogen bonding network which tethers the C-terminal β7α7β8α8 unit to the bulk of the protein. In the variants D227N, D227A, and R191S, this network is preserved, as can be deduced from the structure of the R191S variant. In the R191A variant, the side chain at position 191 cannot contribute to this network. Also the catalytic power of this variant is most affected