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Cell type-specific signal proteins, known as pheromones, are synthesized by ciliated protozoa in association with their self/nonself mating-type systems, and are utilized to control the vegetative growth and mating stages of their life cycle. In species of the most ubiquitous ciliate, Euplotes, these pheromones form families of structurally homologous molecules, which are constitutively secreted into the extracellular environment, from where they can be isolated in sufficient amounts for chemical characterization. This paper describes the NMR structures of En-1 and En-2, which are members of the cold-adapted pheromone family produced by Euplotes nobilii, a species inhabiting the freezing coastal waters of Antarctica. The structures were determined with the proteins from the natural source, using homonuclear (1)H NMR techniques in combination with automated NOESY peak picking and NOE assignment. En-1 and En-2 have highly homologous global folds, which consist of a central three-alpha-helix bundle with an up-down-up topology and a 3(10)-helical turn near the N-terminus. This fold is stabilized by four disulfide bonds and the helices are connected by bulging loops. Apparent structural specificity resides in the variable C-terminal regions of the pheromones. The NMR structures of En-1 and En-2 provide novel insights into the cold-adaptive modifications that distinguish the E. nobilii pheromone family from the closely related E. raikovi pheromone family isolated from temperate waters.  相似文献   

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The MPT64 protein and its homologs form a highly conserved family of secreted proteins with unknown function that are found within the pathogenic Mycobacteria genus. The founding member of this family from Mycobacterium tuberculosis (MPT64 or protein Rv1980c) is expressed only when Mycobacteria cells are actively dividing. By virtue of this relatively unique expression profile, Rv1980c is currently under phase III clinical trials to evaluate its potential to replace tuberculin, or purified protein derivative, as the rapid diagnostic of choice for detection of active tuberculosis infection. We describe here the NMR solution structure of Rv1980c. This structure reveals a previously undescribed fold that is based upon a variation of a beta-grasp motif most commonly found in protein-protein interaction domains. Examination of this structure in conjunction with multiple sequence alignments of MPT64 homologs identifies a candidate ligand-binding site, which may help guide future studies of Rv1980c function. The work presented here also suggests structure-based approaches for increasing the antigenic potency of a Rv1980c-based diagnostic.  相似文献   

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The NMR structure of the Antheraea polyphemus pheromone-binding protein 1 at pH 4.5, ApolPBP1A, was determined at 20 degrees C. The structure consists of six alpha-helices, which are arranged in a globular fold that encapsulates a central helix alpha7 formed by the C-terminal polypeptide segment 131-142. The 3D arrangement of these helices is anchored by the three disulfide bonds 19-54, 50-108 and 97-117, which were identified by NMR. Superposition of the ApolPBP1A structure with the structure of the homologous pheromone-binding protein of Bombyx mori at pH 4.5, BmorPBPA, yielded an rmsd of 1.7 A calculated for the backbone heavy-atoms N, Calpha and C' of residues 10-142. In contrast, the present ApolPBP1A structure is different from a recently proposed molecular model for a low-pH form of ApolPBP1 that does not contain the central helix alpha7. ApolPBP1 exhibits a pH-dependent transition between two different globular conformations in slow exchange on the NMR chemical shift timescale similar to BmorPBP, suggesting that the two proteins use the same mechanism of ligand binding and ejection. The extensive sequence homology observed for pheromone-binding proteins from moth species further implies that the previously proposed mechanism of ligand ejection involving the insertion of a C-terminal helix into the pheromone-binding site is a general feature of pheromone signaling in moths.  相似文献   

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NMR spectroscopy has proven to be a powerful tool for the structure determination of protein/RNA complexes. However, the quality of these structures depends critically on the number of unambiguous intermolecular and intra-RNA nuclear Overhauser effect (NOE) constraints that can be derived. This number is often limited due to exchange phenomena that can cause signal line broadening and the fact that unambiguous NOE assignments are challenging in systems that exchange between different conformations in the intermediate to fast exchange limit. These exchange processes can include exchange between free and bound form, as well as exchange of the ligand between different binding sites on the protein. Furthermore, for the large class of RNA metabolizing proteins that bind repetitive low-complexity RNA sequences in multiple register, exchange of the protein between these overlapping binding sites introduces additional exchange pathways. Here, we describe the strategy we used to overcome these exchange processes and to reduce significantly the line width of the RNA resonances in complexes of the RNA recognition motifs (RRMs) of the polypyrimidine tract-binding protein (PTB) in complex with pyrimidine tracts and hence allowed a highly precise structure determination. This method could be employed to derive structures of other protein/single-stranded nucleic acid complexes by NMR spectroscopy. Furthermore, we have determined the affinities of the individual RRMs of PTB for pyrimidine tracts of different length and sequence. These measurements show that PTB binds preferentially to long pyrimidine tracts that contain cytosine and hence confirm the structure of PTB in complex with RNA. Furthermore, they provide quantitative insight into the question of which pyrimidine sequences within alternatively spliced pre-mRNAs will be preferentially bound by PTB.  相似文献   

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Tropomyosin is a coiled-coil protein that binds head-to-tail along the length of actin filaments in eukaryotic cells, stabilizing them and providing protection from severing proteins. Tropomyosin cooperatively regulates actin's interaction with myosin and mediates the Ca2+ -dependent regulation of contraction by troponin in striated muscles. The N-terminal and C-terminal ends are critical functional determinants that form an "overlap complex". Here we report the solution NMR structure of an overlap complex formed of model peptides. In the complex, the chains of the C-terminal coiled coil spread apart to allow insertion of 11 residues of the N-terminal coiled coil into the resulting cleft. The plane of the N-terminal coiled coil is rotated 90 degrees relative to the plane of the C terminus. A consequence of the geometry is that the orientation of postulated periodic actin binding sites on the coiled-coil surface is retained from one molecule to the next along the actin filament when the overlap complex is modeled into the X-ray structure of tropomyosin determined at 7 Angstroms. Nuclear relaxation NMR data reveal flexibility of the junction, which may function to optimize binding along the helical actin filament and to allow mobility of tropomyosin on the filament surface as it switches between regulatory states.  相似文献   

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The capsular polysaccharide from Streptococcus pneumoniae Type 15B is a component of the 23-valent polysaccharide vaccine against pneumococcal disease. We report full NMR assignments for the native and de-O-acetylated polysaccharide, and confirm that the phosphorylated substituent is glycerol-2-phosphate rather than phosphocholine, located on O-3 of the side chain beta-Galp residue. The polysaccharide is O-acetylated on the terminal alpha-Gal residue, distributed between O-2, O-3, O-4 and O-6 in a ratio of 6:12:12:55, with approximately 15% of the repeat units not O-acetylated.  相似文献   

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The three-dimensional structure of the outer membrane protein A from Klebsiella pneumoniae transmembrane domain was determined by NMR. This protein induces specific humoral and cytotoxic responses, and is a potent carrier protein. This is one of the largest integral membrane proteins (210 residues) for which nearly complete resonance assignment, including side chains, has been achieved so far. The methodology rested on the use of 900 MHz 3D and 4D TROSY experiments recorded on a uniformly 15N,13C,2H-labeled sample and on a perdeuterated methyl protonated sample. The structure was refined from 920 experimental constraints, giving an ensemble of 20 best structures with an r.m.s. deviation of 0.54 Å for the main chain atoms in the core eight-stranded β-barrel. The protein dynamics was assessed, in a residue-specific manner, by 1H-15N NOEs (pico- to nanosecond timescale), exchange broadening (millisecond to second) and 1H-2H chemical exchange (hour-weeks).  相似文献   

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CHD7 is a member of the chromodomain helicase DNA binding domain (CHD) family of ATP-dependent chromatin remodelling enzymes. It is mutated in CHARGE syndrome, a multiple congenital anomaly condition. CHD7 is one of a subset of CHD proteins, unique to metazoans that contain the BRK domain, a protein module also found in the Brahma/BRG1 family of helicases. We describe here the NMR solution structure of the two BRK domains of CHD7. Each domain has a compact betabetaalphabeta fold. The second domain has a C-terminal extension consisting of two additional helices. The structure differs from those of other domains present in chromatin-associated proteins.  相似文献   

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Type 1 pili from uropathogenic Escherichia coli strains mediate bacterial attachment to target receptors on the host tissue. They are composed of up to 3000 copies of the subunit FimA, which form the stiff, helical pilus rod, and the subunits FimF, FimG, and FimH, which form the linear tip fibrillum. All subunits in the pilus interact via donor strand complementation, in which the incomplete immunoglobulin-like fold of each subunit is complemented by insertion of an N-terminal extension from the following subunit. We determined the NMR structure of a monomeric, self-complemented variant of FimF, FimFF, which has a second FimF donor strand segment fused to its C-terminus that enables intramolecular complementation of the FimF fold. NMR studies on bimolecular complexes between FimFF and donor strand-depleted variants of FimF and FimG revealed that the relative orientations of neighboring domains in the tip fibrillum cover a wide range. The data provide strong support for the intrinsic flexibility of the tip fibrillum. They lend further support to the hypothesis that this flexibility would significantly increase the probability that the adhesin at the distal end of the fibrillum successfully targets host cell receptors.  相似文献   

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Beclin-1, originally identified as a Bcl-2 binding protein, is an evolutionarily conserved protein required for autophagy. The direct interaction between Beclin-1 and Bcl-2 or Bcl-xL provides a potential convergence point for apoptosis and autophagy, two programmed cell death processes. Given the functional significance of the interaction between Beclin-1 and Bcl-2/Bcl-xL, we performed detailed biochemical and structural characterizations of this interaction. We demonstrated that the Bcl-xL-binding domain of Beclin-1 contains a BH3 domain. Therefore, Beclin-1 is a new member of the BH3-only family proteins. The structure of Bcl-xL in complex with the Beclin-1 BH3 domain was determined at high resolution by NMR spectroscopy. Although similar to other known BH3 domains, the Beclin-1 BH3 domain displays its own distinct features in the complex with Bcl-xL. Systematic analysis of all known Bcl-xL/BH3 domain complexes helped us to identify the molecular basis underlying the capacity of Bcl-xL to recognize diverse target sequences.  相似文献   

13.
Computational protein design procedures were applied to the redesign of the entire sequence of a 51 amino acid residue protein, Drosophila melanogaster engrailed homeodomain. Various sequence optimization algorithms were compared and two resulting designed sequences were experimentally evaluated. The two sequences differ by 11 mutations and share 22% and 24% sequence identity with the wild-type protein. Both computationally designed proteins were considerably more stable than the naturally occurring protein, with midpoints of thermal denaturation greater than 99 degrees C. The solution structure was determined for one of the two sequences using multidimensional heteronuclear NMR spectroscopy, and the structure was found to closely match the original design template scaffold.  相似文献   

14.
The study of multidomain or large proteins in solution by NMR spectroscopy has been made possible in recent years by the development of new spectroscopic methods. However, resonance overlap found in large proteins remains a limiting factor, making resonance assignments and structure determination of large proteins very difficult. In this study, we present an expressed protein ligation protocol that can be used for the segmental isotopic labeling of virtually any multidomain or high molecular mass protein, independent of both the folding state and the solubility of the protein fragments, as well as independent of whether the fragments are interacting. The protocol was applied successfully to two different multidomain proteins containing RNA recognition motifs (RRMs), heterogeneous nuclear ribonucleoprotein L and Npl3p. High yields of segmentally labeled proteins could be obtained, allowing characterization of the interdomain interactions with NMR spectroscopy. We found that the RRMs of heterogeneous nuclear ribonucleoprotein L interact, whereas those of Npl3p are independent. Subsequently, the structures of the two RRMs of Npl3p were determined on the basis of samples in which each RRM was expressed individually. The two Npl3p RRMs adopt the expected βαββαβ fold.  相似文献   

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GABAB receptor is a G protein-coupled receptor for GABA and drug target for neurological and psychiatric disorders. From the analysis of GTPγS binding assay, we found that a synthesized peptide (GABAb: ETKSVSTEKINDHR) corresponding to the intracellular third loop region of metabotropic GABAB receptor could activate Gi protein α subunit directly. The three dimensional molecular structure of the peptide in SDS-d25 micelles was determined by 2D 1H-NMR spectroscopy. GABAb peptide formed an α helical structure and a positive charge cluster at the C-terminal site. These structural features were also found in several other G protein activating peptides. From the comparison among these peptides, we found that peptides with high helical content show the high activity.  相似文献   

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The genome of the opportunistic pathogen Clostridium perfringens encodes a large number of secreted glycoside hydrolases. Their predicted activities indicate that they are involved in the breakdown of complex carbohydrates and other glycans found in the mucosal layer of the human gastrointestinal tract, within the extracellular matrix, and on the surface of host cells. One such group of these enzymes is the family 84 glycoside hydrolases, which has predicted hyaluronidase activity and comprises five members [C. perfringens glycoside hydrolase family 84 (CpGH84) A-E]. The first identified member, CpGH84A, corresponds to the μ-toxin whose modular architecture includes an N-terminal catalytic domain, four family 32 carbohydrate-binding modules, three FIVAR modules of unknown function, and a C-terminal putative calcium-binding module. Here, we report the solution NMR structure of the C-terminal modular pair from the μ-toxin. The three-helix bundle FIVAR module displays structural homology to a heparin-binding module within the N-terminal of the a C protein from group B Streptoccocus. The C-terminal module has a typical calcium-binding dockerin fold comprising two anti-parallel helices that form a planar face with EF-hand calcium-binding loops at opposite ends of the module. The size of the helical face of the μ-toxin dockerin module is approximately equal to the planar region recently identified on the surface of a cohesin-like X82 module of CpGH84C. Size-exclusion chromatography and heteronuclear NMR-based chemical shift mapping studies indicate that the helical face of the dockerin module recognizes the CpGH84C X82 module. These studies represent the structural characterization of a noncellulolytic dockerin module and its interaction with a cohesin-like X82 module. Dockerin/X82-mediated enzyme complexes may have important implications in the pathogenic properties of C. perfringens.  相似文献   

18.
The NMR structure of the pheromone Er-2 from the ciliated protozoan Euplotes raikovi has been determined in aqueous solution. The structure of this 40-residue protein was calculated with the distance geometry program DIANA from 621 distance constraints and 89 dihedral angle constraints; the program OPAL was employed for the energy minimization. For a group of 20 conformers used to characterize the solution structure, the average pairwise RMS deviation from the mean structure calculated for the backbone heavy atoms N, C alpha, and C' of residues 3-37 was 0.31 A. The molecular architecture is dominated by an up-down-up bundle of 3 short helices of residues 5-11, 14-20, and 23-33, which is similar to the structures of the homologous pheromones Er-1 and Er-10. Novel structural features include a well-defined N-cap on the first helix, a 1-residue deletion in the second helix resulting in the formation of a 3(10)-helix rather than an alpha-helix as found in Er-1 and Er-10, and the simultaneous presence of 2 different conformations for the C-terminal tetrapeptide segment, i.e., a major conformation with the Leu 39-Pro 40 peptide bond in the trans form and a minor conformation with this peptide bond in the cis form.  相似文献   

19.
Interruptions in the repeating (Gly-X1-X2)n amino acid sequence pattern are found in the triple-helix domains of all non-fibrillar collagens, and perturbations to the triple-helix at such sites are likely to play a role in collagen higher-order structure and function. This study defines the sequence features and structural consequences of the most common interruption, where one residue is missing from the tripeptide pattern, Gly-X1-X2-Gly-AA1-Gly-X1-X2, designated G1G interruptions. Residues found within G1G interruptions are predominantly hydrophobic (70%), followed by a significant amount of charged residues (16%), and the Gly-X1-X2 triplets flanking the interruption are atypical. Studies on peptide models indicate the degree of destabilization is much greater when Pro is in the interruption, GP, than when hydrophobic residues (GF, GY) are present, and a rigid Gly-Pro-Hyp tripeptide adjacent to the interruption leads to greater destabilization than a flexible Gly-Ala-Ala sequence. Modeling based on NMR data indicates the Phe residue within a GF interruption is located on the outside of the triple helix. The G1G interruptions resemble a previously studied collagen interruption GPOGAAVMGPO, designated G4G-type, in that both are destabilizing, but allow continuation of rod-like triple helices and maintenance of the single residue stagger throughout the imperfection, with a loss of axial register of the superhelix on both sides. Both kinds of interruptions result in a highly localized perturbation in hydrogen bonding and dihedral angles, but the hydrophobic residue of a G4G interruption packs near the central axis of the superhelix, while the hydrophobic residue of a G1G interruption is located on the triple-helix surface. The different structural consequences of G1G and G4G interruptions in the repeating tripeptide sequence pattern suggest a physical basis for their differential susceptibility to matrix metalloproteinases in type X collagen.  相似文献   

20.
Chi LM  Lam SL 《FEBS letters》2006,580(27):6496-6500
Slipped frameshift intermediates can occur when DNA polymerase slows or stalls at sites of DNA lesions. However, this phenomenon is much less common when unmodified DNA is replicated. In order to study the effect of templating bases on the alignment of primer-templates, NMR structural investigation has been performed on primer-template oligonucleotide models which mimic the situation that dNTP has just been incorporated opposite template. NMR evidence reveals the occurrence of misalignment when dGTP is incorporated opposite template T with a downstream nucleotide C. Depending on the template sequence, further extension of the primer can lead to realignment.  相似文献   

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