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Miquel Coll

Publications and source records attributed to Miquel Coll.

At least 19 recordsLinked to original sources
PubMed2006

The X-ray crystal structures of two constitutively active mutants of the Escherichia coli PhoB receiver domain give insights into activation.

The PhoR/PhoB two-component system is a key regulatory protein network enabling Escherichia coli to respond to inorganic phosphate (Pi) starvation conditions by turning on Pho regulon genes for more efficient Pi uptake and use of alternative phosphorus sources. Under environmental Pi depletion, the response regulator (RR) component, PhoB, is phosphorylated at the receiver domain (RD), a process that requires Mg(2+) bound at the active site. Phosphorylation of the RD relieves the inhibition of the PhoB effector domain (ED), a DNA-binding region that binds to Pho regulon promoters to activate transcription. The molecular details of the activation are proposed to involve dimerization of the RD and a conformational change in the RD detected by the ED. The structure of the PhoB RD shows a symmetrical interaction involving alpha1, loop beta5alpha5 and N terminus of alpha5 elements, also seen in the complex of PhoB RD with Mg(2+), in which helix alpha4 highly increases its flexibility. PhoB RD in complex with Mg(2+) and BeF(3) (an emulator of the phosphate moiety) undergoes a dramatic conformational change on helix alpha4 and shows another interaction involving alpha4, beta5 and alpha5 segments. We have selected a series of constitutively active PhoB mutants (PhoB(CA)) that are able to turn on the Pho regulon promoters in the absence phosphorylation and, as they cannot be inactivated, should therefore mimic the active RD state of PhoB and its functional oligomerisation. We have analysed the PhoB(CA) RD crystal structures of two such mutants, Asp53Ala/Tyr102Cys and Asp10Ala/Asp53Glu. Interestingly, both mutants reproduce the homodimeric arrangement through the symmetric interface encountered in the unbound and magnesium-bound wild-type PhoB RD structures. Besides, the mutant RD structures show a modified active site organization as well as changes at helix alpha4 that correlate with repositioning of surrounding residues, like the active-site events indicator Trp54, putatively redifining the interaction with the ED in the full-length protein.

Amino Acid Motifs↗
PubMed2006

Cut and move: protein machinery for DNA processing in bacterial conjugation.

Conjugation is a paradigmatic example of horizontal or lateral gene transfer, whereby DNA is translocated between bacterial cells. It provides a route for the rapid acquisition of new genetic information. Increased antibiotic resistance among pathogens is a troubling consequence of this microbial capacity. DNA transfer across cell membranes requires a sophisticated molecular machinery that involves the participation of several proteins in DNA processing and replication, cell recruitment, and the transport of DNA and proteins from donor to recipient cells. Although bacterial conjugation was first reported in the 1940s, only now are we beginning to unravel the molecular mechanisms behind this process. In particular, structural biology is revealing the detailed molecular architecture of several of the pieces involved.

Bacteria↗
PubMed2006

The cofactor-induced pre-active conformation in PhoB.

PhoB is an Escherichia coli transcription factor from a two-component signal transduction system that is sensitive to limiting environmental phosphate conditions. It consists of an N-terminal receiver domain (RD) and a C-terminal DNA-binding domain. The protein is activated upon phosphorylation at the RD, an event that depends on Mg(2+) binding. The structure of PhoB RD in complex with Mg(2+) is presented, which shows three protomers in the asymmetric unit that interact across two different surfaces. One association is symmetric and has been described as a non-active dimerization contact; the other involves the alpha4-beta5-alpha5 interface and recalls the contact found in activated PhoB. However, here this last interaction is not perfectly symmetric and helix alpha4, which in the activated molecule undergoes a helical shift, becomes strongly destabilized in one of the interacting monomers. All protomers bind the cation in a similar manner but, interestingly, at the prospective binding site for the phosphate moiety the side chains of either Glu88 (in helix alpha4) or Trp54 alternate and interact with active-site atoms. When Glu88 is inside the cavity, helix alpha4 is arranged similarly to the unliganded wild-type structure. However, if Trp54 is present, the helix loses its contacts with the active-site cavity and vanishes. Accordingly, the presence of Trp54 in the active site induces a flexible state in helix alpha4, potentially allowing a helical shift that phosphorylation would eventually stabilize.

Bacterial Proteins↗
PubMed2006

The structure of phage phi29 transcription regulator p4-DNA complex reveals an N-hook motif for DNA.

Protein p4 affects the transcriptional switch that divides bacteriophage phi29 infection in early and late phases. The synthesis of DNA replication proteins and p4 takes place in the early phase, while structural, morphogenesis, and lysis proteins are synthesized in the late phase. Transcriptional switch by p4 is achieved by activating the late promoter A3 and repressing the early promoters A2b and A2c. The crystal structure of p4 alone and in complex with a 41 bp DNA, including the A3 promoter binding site, helps us to understand how the phage cycle is controlled. Protein p4 has a unique alpha/beta fold that includes a DNA recognition motif consisting of two N-terminal beta turn substructures, or N-hooks, located at the tips of an elongated protein homodimer. The two N-hooks enter the major groove of the double helix, establishing base-specific contacts. A high DNA curvature allows p4 N-hooks to reach two major groove areas three helical turns apart, like a bow and its string.

Amino Acid Motifs↗
PubMed2006

Unveiling the molecular mechanism of a conjugative relaxase: The structure of TrwC complexed with a 27-mer DNA comprising the recognition hairpin and the cleavage site.

TrwC is a DNA strand transferase that catalyzes the initial and final stages of conjugative DNA transfer. We have solved the crystal structure of the N-terminal relaxase domain of TrwC in complex with a 27 base-long DNA oligonucleotide that contains both the recognition hairpin and the scissile phosphate. In addition, a series of ternary structures of protein-DNA complexes with different divalent cations at the active site have been solved. Systematic anomalous difference analysis allowed us to determine unambiguously the nature of the metal bound. Zn2+, Ni2+ and Cu2+ were found to bind the histidine-triad metal binding site. Comparison of the structures of the different complexes suggests two pathways for the DNA to exit the active pocket. They are probably used at different steps of the conjugative DNA-processing reaction. The structural information allows us to propose (i) an enzyme mechanism where the scissile phosphate is polarized by the metal ion facilitating the nucleophilic attack of the catalytic tyrosine, and (ii) a probable sequence of events during conjugative DNA processing that explains the biological function of the relaxase.

Binding Sites↗
PubMed2005

The anticancer agent ellipticine unwinds DNA by intercalative binding in an orientation parallel to base pairs.

Ellipticine is a natural plant product that has been found to be a powerful anticancer drug. Although still unclear, its mechanism of action is considered to be mainly based on DNA intercalation and/or the inhibition of topoisomerase II. Many experimental data suggest an intercalation based on stacking interactions along the major base-pair axis, but alternative binding modes have been proposed, in particular for ellipticine derivatives. The 1.5 A resolution structure of ellipticine complexed to a 6 bp oligonucleotide unveils its mode of binding and enables a detailed analysis of the distorting effects of the drug on the DNA.

Antineoplastic Agents↗
PubMed2005

Crystal structure of an iron-dependent group III dehydrogenase that interconverts L-lactaldehyde and L-1,2-propanediol in Escherichia coli.

The FucO protein, a member of the group III "iron-activated" dehydrogenases, catalyzes the interconversion between L-lactaldehyde and L-1,2-propanediol in Escherichia coli. The three-dimensional structure of FucO in a complex with NAD(+) was solved, and the presence of iron in the crystals was confirmed by X-ray fluorescence. The FucO structure presented here is the first structure for a member of the group III bacterial dehydrogenases shown experimentally to contain iron. FucO forms a dimer, in which each monomer folds into an alpha/beta dinucleotide-binding N-terminal domain and an all-alpha-helix C-terminal domain that are separated by a deep cleft. The dimer is formed by the swapping (between monomers) of the first chain of the beta-sheet. The binding site for Fe(2+) is located at the face of the cleft formed by the C-terminal domain, where the metal ion is tetrahedrally coordinated by three histidine residues (His200, His263, and His277) and an aspartate residue (Asp196). The glycine-rich turn formed by residues 96 to 98 and the following alpha-helix is part of the NAD(+) recognition locus common in dehydrogenases. Site-directed mutagenesis and enzyme kinetic assays were performed to assess the role of different residues in metal, cofactor, and substrate binding. In contrast to previous assumptions, the essential His267 residue does not interact with the metal ion. Asp39 appears to be the key residue for discriminating against NADP(+). Modeling L-1,2-propanediol in the active center resulted in a close approach of the C-1 hydroxyl of the substrate to C-4 of the nicotinamide ring, implying that there is a typical metal-dependent dehydrogenation catalytic mechanism.

Aldehydes↗
PubMed2004

On the transcriptional regulation of methicillin resistance: MecI repressor in complex with its operator.

Bacterial resistance to antibiotics poses a serious worldwide public health problem due to the high morbidity and mortality caused by infectious diseases. Most hospital-onset infections are associated with methicillin-resistant Staphylococcus aureus (MRSA) strains that have acquired multiple drug resistance to beta-lactam antibiotics. In a response to antimicrobial stress, nearly all clinical MRSA isolates produce beta-lactamase (BlaZ) and a penicillin-binding protein with low affinity for beta-lactam antibiotics (PBP2a, also known as PBP2' or MecA). Both effectors are regulated by homologous signal transduction systems consisting of a sensor/transducer and a transcriptional repressor. MecI (methicillin repressor) blocks mecA but also blaZ transcription and that of itself and the co-transcribed sensor/transducer. The structure of MecI in complex with a cognate operator double-stranded DNA reveals a homodimeric arrangement with a novel C-terminal spiral staircase dimerization domain responsible for dimer integrity. Each protomer interacts with the DNA major groove through a winged helix DNA-binding domain and specifically recognizes the nucleotide sequence 5'-Gua-Thy-Ade-X-Thy-3'. This results in an unusual convex bending of the DNA helix. The structure of this first molecular determinant of methicillin resistance in complex with its target DNA provides insights into its regulatory mechanism and paves the way for new antimicrobial strategies against MRSA.

Amino Acid Sequence↗
PubMed2003

Recognition and processing of the origin of transfer DNA by conjugative relaxase TrwC.

Relaxases are DNA strand transferases that catalyze the initial and final stages of DNA processing during conjugative cell-to-cell DNA transfer. Upon binding to the origin of transfer (oriT) DNA, relaxase TrwC melts the double helix. The three-dimensional structure of the relaxase domain of TrwC in complex with its cognate DNA at oriT shows a fold built on a two-layer alpha/beta sandwich, with a deep narrow cleft that houses the active site. The DNA includes one arm of an extruded cruciform, an essential feature for specific recognition. This arm is firmly embraced by the protein through a beta-ribbon positioned in the DNA major groove and a loop occupying the minor groove. It is followed by a single-stranded DNA segment that enters the active site, after a sharp U-turn forming a hydrophobic cage that traps the N-terminal methionine. Structural analysis combined with site-directed mutagenesis defines the architecture of the active site.

Amino Acid Sequence↗
PubMed2003

Three-dimensional structure of MecI. Molecular basis for transcriptional regulation of staphylococcal methicillin resistance.

Methicillin-resistant Staphylococcus aureus is the main cause of nosocomial and community-onset infections that affect millions of people worldwide. Some methicillin-resistant Staphylococcus aureus infections have become essentially untreatable by beta-lactams because of acquired molecular machineries enabling antibiotic resistance. Evasion from methicillin challenge is mainly achieved by the synthesis of a penicillin-binding protein of low affinity for antibiotics, MecA, that replaces regular penicillin-binding proteins in cell wall turnover when these have been inactivated by antibiotics. MecA synthesis is regulated by a signal transduction system consisting of the sensor/transducer MecR1 and the 14-kDa transcriptional repressor MecI (also known as methicillin repressor) that constitutively blocks mecA transcription. The three-dimensional structure of MecI reveals a dimer of two independent winged helix domains, each of which binds a palindromic DNA-operator half site, and two intimately intertwining dimerization domains of novel spiral staircase architecture, held together by a hydrophobic core. Limited proteolytic cleavage by cognate MecR1 within the dimerization domains results in loss of dimer interaction surface, dissociation, and repressor release, which triggers MecA synthesis. Structural information on components of the MecA regulatory pathway, in particular on methicillin repressor, the ultimate transcriptional trigger of mecA-encoded methicillin resistance, is expected to lead to the development of new antimicrobial drugs.

Amino Acid Sequence↗
PubMed2003

Structure of xylanase Xys1delta from Streptomyces halstedii.

Xylanases hydrolyze the beta-1,4-linked xylose backbone of xylans. They are of increasing interest in the paper and food industries for their pre-bleaching and bio-pulping applications. Such industries demand new xylanases to cover a wider range of cleavage specificity, activity and stability. The catalytic domain of xylanase Xys1 from Streptomyces halstedii JM8 was expressed, purified and crystallized and native data were collected to 1.78 A resolution with an R(merge) of 4.4%. The crystals belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 34.05, b = 79.60, c = 87.80 A. The structure was solved by the molecular-replacement method using the structure of the homologue Xyl10A from Streptomyces lividans. In a similar manner to other members of its family, Xys1 folds to form a standard (beta/alpha)(8) barrel with the two catalytic functions, the acid/base and the nucleophile, at its C-terminal side. The overall structure is described and compared with those of related xylanases.

Amino Acid Sequence↗
PubMed2002

Human procarboxypeptidase B: three-dimensional structure and implications for thrombin-activatable fibrinolysis inhibitor (TAFI).

Besides their classical role in alimentary protein degradation, zinc-dependant carboxypeptidases also participate in more selective regulatory processes like prohormone and neuropeptide processing or fibrinolysis inhibition in blood plasma. Human pancreatic procarboxypeptidase B (PCPB) is the prototype for those human exopeptidases that cleave off basic C-terminal residues and are secreted as inactive zymogens. One such protein is thrombin-activatable fibrinolysis inhibitor (TAFI), also known as plasma PCPB, which circulates in human plasma as a zymogen bound to plasminogen. The structure of human pancreatic PCPB displays a 95-residue pro-segment consisting of a globular region with an open-sandwich antiparallel-alpha antiparallel-beta topology and a C-terminal alpha-helix, which connects to the enzyme moiety. The latter is a 309-amino acid residue catalytic domain with alpha/beta hydrolase topology and a preformed active site, which is shielded by the globular domain of the pro-segment. The fold of the proenzyme is similar to previously reported procarboxypeptidase structures, also in that the most variable region is the connecting segment that links both globular moieties. However, the empty active site of human procarboxypeptidase B has two alternate conformations in one of the zinc-binding residues, which account for subtle differences in some of the key residues for substrate binding. The reported crystal structure, refined with data to 1.6A resolution, permits in the absence of an experimental structure, accurate homology modelling of TAFI, which may help to explain its properties.

Amino Acid Sequence↗
PubMed2002

The inherent properties of DNA four-way junctions: comparing the crystal structures of holliday junctions.

Holliday junctions are four-stranded DNA complexes that are formed during recombination and related DNA repair events. Much work has focused on the overall structure and properties of four-way junctions in solution, but we are just now beginning to understand these complexes at the atomic level. The crystal structures of two all-DNA Holliday junctions have been determined recently from the sequences d(CCGGGACCGG) and d(CCGGTACCGG). A detailed comparison of the two structures helps to distinguish distortions of the DNA conformation that are inherent to the cross-overs of the junctions in this crystal system from those that are consequences of the mismatched dG.dA base-pair in the d(CCGGGACCGG) structure. This analysis shows that the junction itself perturbs the sequence-dependent conformational features of the B-DNA duplexes and the associated patterns of hydration in the major and minor grooves only minimally. This supports the idea that a DNA four-way junction can be assembled at relatively low energetic cost. Both structures show a concerted rotation of the adjacent duplex arms relative to B-DNA, and this is discussed in terms of the conserved interactions between the duplexes at the junctions and further down the helical arms. The interactions distant from the strand cross-overs of the junction appear to be significant in defining its macroscopic properties, including the angle relating the stacked duplexes across the junction.

Base Pair Mismatch↗
PubMed2002

The structure of human prokallikrein 6 reveals a novel activation mechanism for the kallikrein family.

Zyme/protease M/neurosin/human kallikrein 6 (hK6) is a member of the human kallikrein family of trypsin-like serine proteinases and was originally identified as being down-regulated in metastatic breast and ovarian tumors when compared with corresponding primary tumors. Recent evidence suggests that hK6 may serve as a circulating tumor marker in ovarian cancers. In addition, it was described in the brain of Parkinson's disease and Alzheimer's disease patients, where it is implicated in amyloid precursor protein processing. It is thus a biomarker for these diseases. To examine the mechanism of activation of hK6, we have solved the structure of its proform, the first of a human kallikrein family member. The proenzyme displays a fold that exhibits chimeric features between those of trypsinogen and other family members. It lacks the characteristic "kallikrein loop" and forms the six disulfide bridges of trypsin. Pro-hK6 displays a completely closed specificity pocket and a unique conformation of the regions involved in structural rearrangements upon proteolytic cleavage activation. This points to a novel activation mechanism, which could be extrapolated to other human kallikreins.

Amino Acid Sequence↗
PubMed2002

Three-dimensional structure of human tubulin chaperone cofactor A.

alpha and beta-Tubulin fold in a series of chaperone-assisted steps. At least five protein cofactors are involved in the post-chaperonin tubulin folding pathway and required to maintain the supply of tubulin; some of them also participate in microtubule dynamics. The first tubulin chaperone identified in the tubulin folding pathway was cofactor A (CoA). Here we describe the three-dimensional structure of human CoA at 1.7 A resolution, determined by multiwavelength anomalous diffraction (MAD). The structure is a monomer with a rod-like shape and consists of a three-alpha-helix bundle, or coiled coil, with the second helix kinked by a proline break, offering a convex surface at one face of the protein. The helices are connected by short turns, one of them, between alpha2 and alpha3, including a 3(10)-helix. Peptide mapping analysis and competition experiments with peptides show that CoA interacts with beta-tubulin via the three alpha-helical regions but not with the rod-end loops. The main interaction occurs with the middle kinked alpha2 helix, at the convex face of the rod. Strong 3D structural homology is found with the Hsp70 chaperone cofactor BAG domain, suggesting that these proteins define a family of cofactors of simple compact architecture. Further structural homology is found with alpha-spectrin/alpha-actinin repeats, all are rods of identical length of ten helical turns. We propose to call these three-helix bundles alpha ten modules.

Actinin↗
PubMed2002

Detailed architecture of a DNA translocating machine: the high-resolution structure of the bacteriophage phi29 connector particle.

The three-dimensional crystal structure of the bacteriophage phi29 connector has been solved and refined to 2.1A resolution. This 422 kDa oligomeric protein connects the head of the phage to its tail and translocates the DNA into the prohead during packaging. Each monomer has an elongated shape and is composed of a central, mainly alpha-helical domain that includes a three-helix bundle, a distal alpha/beta domain and a proximal six-stranded SH3-like domain. The protomers assemble into a 12-mer, propeller-like, super-structure with a 35 A wide central channel. The surface of the channel is mainly electronegative, but it includes two lysine rings 20 A apart. On the external surface of the particle a hydrophobic belt extends to the concave area below the SH3-like domain, which forms a crown that retains the particle in the head. The lipophilic belt contacts the non-matching symmetry vertex of the capsid and forms a bearing for the connector rotation. The structure suggests a translocation mechanism in which the longitudinal displacement of the DNA along its axis is coupled to connector spinning.

Amino Acid Sequence↗
PubMed2002

Structure and role of coupling proteins in conjugal DNA transfer.

Type IV secretory systems are transmembrane bacterial multiprotein complexes. They are pivotal for conjugation, bacterial-induced plant tumour formation, toxin secretion and mammalian pathogen intracellular activity. These systems are involved in the spread of antibiotic resistance genes among bacteria by enabling conjugative DNA transfer. When such translocons transport DNA, they require the assistance of multimeric integral inner membrane proteins, the type IV coupling proteins. Its structural prototype is plasmid R388 TrwB protein, responsible for coupling the relaxosome with the DNA transport apparatus during bacterial conjugation. Its monomeric molecular structure is reminiscent of ring helicases and AAA ATPases. The quaternary structure is made up by six equivalent protomers featuring a flattened sphere resembling F1-ATPase, with a central channel traversing the particle, thus connecting cytoplasm and periplasm.

Bacteria↗