Non-canonical Staphylococcus aureus pathogenicity island repression.

Mobile genetic elements control their life cycles by the expression of a master repressor, whose function must be disabled to allow the spread of these elements in nature. Here, we describe an unprecedented repression-derepression mechanism involved in the transfer of Staphylococcus aureus pathogenicity islands (SaPIs). Contrary to the classical phage and SaPI repressors, which are dimers, the SaPI1 repressor StlSaPI1 presents a unique tetrameric conformation never seen before.

Hijacking the Hijackers: Escherichia coli Pathogenicity Islands Redirect Helper Phage Packaging for Their Own Benefit.

Phage-inducible chromosomal islands (PICIs) represent a novel and universal class of mobile genetic elements, which have broad impact on bacterial virulence. In spite of their relevance, how the Gram-negative PICIs hijack the phage machinery for their own specific packaging and how they block phage reproduction remains to be determined. Using genetic and structural analyses, we solve the mystery here by showing that the Gram-negative PICIs encode a protein that simultaneously performs these processes.

The role of water molecules in the binding of class I and II peptides to the SH3 domain of the Fyn tyrosine kinase.

Interactions of proline-rich motifs with SH3 domains are present in signal transduction and other important cell processes. Analysis of structural and thermodynamic data suggest a relevant role of water molecules in these protein-protein interactions. To determine whether or not the SH3 domain of the Fyn tyrosine kinase shows the same behaviour, the crystal structures of its complexes with two high-affinity synthetic peptides, VSL12 and APP12, which are class I and II peptides, respectively, have been solved.

The Monomeric Species of the Regulatory Domain of Tyrosine Hydroxylase Has a Low Conformational Stability.

Tyrosine hydroxylase (TyrH) catalyzes the hydroxylation of tyrosine to form 3,4-dihydroxyphenylalanine, the first step in the synthesis of catecholamine neurotransmitters. The protein contains a 159-residue regulatory domain (RD) at its N-terminus that forms dimers in solution; the N-terminal region of RDTyrH (residues 1-71) is absent in the solution structure of the domain. We have characterized the conformational stability of two species of RDTyrH (one containing the N-terminal region and another lacking the first 64 residues) to clarify how that N-terminal region modulates the conformational stability of RD.

New crystal form of human ubiquitin in the presence of magnesium.

Ubiquitin is a small globular protein that has a considerable number of lysine residues on its surface. This results in a high surface entropy that precludes the formation of crystal-packing interactions. To date, only a few structures of the native form of ubiquitin have been solved, and most of the crystals that led to these structures were obtained in the presence of different divalent metal cations.

Crystal structure of the first WW domain of human YAP2 isoform.

The WW domains are the smallest modular domains known. The study of the structural basis of their stability is important to understand their physiological role. These domains are intrinsically flexible, which makes them difficult to crystallize.

Electrostatic effects in the folding of the SH3 domain of the c-Src tyrosine kinase: pH-dependence in 3D-domain swapping and amyloid formation.

The SH3 domain of the c-Src tyrosine kinase (c-Src-SH3) aggregates to form intertwined dimers and amyloid fibrils at mild acid pHs. In this work, we show that a single mutation of residue Gln128 of this SH3 domain has a significant effect on: (i) its thermal stability; and (ii) its propensity to form amyloid fibrils. The Gln128Glu mutant forms amyloid fibrils at neutral pH but not at mild acid pH, while Gln128Lys and Gln128Arg mutants do not form these aggregates under any of the conditions assayed.

Structure of the c-Src-SH3 domain in complex with a proline-rich motif of NS5A protein from the hepatitis C virus.

The non-structural hepatitis C virus proteins NS5A and NS5B form a complex through interaction with the SH2 and SH3 domains of the non-receptor Src tyrosine kinase, which seems essential for viral replication. We have crystallized the complex between the SH3 domain of the c-Src tyrosine kinase and the C-terminal proline rich motif of the NS5A protein (A349PPIPPPRRKR359). Crystals obtained at neutral pH belong to the space group I41, with a single molecule of the SH3/NS5A complex at the asymmetric unit.

The isolated N terminus of Ring1B is a well-folded, monomeric fragment with native-like structure.

The Polycomb group (PcG) proteins assemble into Polycomb repressive complexes (PRCs), PRC1 and PRC2, which act as general transcriptional repressors. PRC1 comprises a variety of biochemical entities endowed with histone H2A monoubiquitylation activity conferred by really interesting new gene (RING) finger E3 ubiquitin ligases Ring1A and Ring1B. All PRC1 complexes contain Ring1 proteins which are essential for Polycomb epigenetic regulation.

The histidine-phosphocarrier protein of the phosphoenolpyruvate: sugar phosphotransferase system of Bacillus sphaericus self-associates.

The phosphotransferase system (PTS) is involved in the use of carbon sources in bacteria. Bacillus sphaericus, a bacterium with the ability to produce insecticidal proteins, is unable to use hexoses and pentoses as the sole carbon source, but it has ptsHI genes encoding the two general proteins of the PTS: enzyme I (EI) and the histidine phosphocarrier (HPr). In this work, we describe the biophysical and structural properties of HPr from B.

Atomic resolution structures of the c-Src SH3 domain in complex with two high-affinity peptides from classes I and II.

The atomic resolution crystal structures of complexes between the SH3 domain of the c-Src tyrosine kinase and two high-affinity peptides belonging to class I and class II have been solved. The crystals of the Thr98Asp and Thr98Glu mutants in complex with the APP12 peptide (APPLPPRNRPRL) belonged to the trigonal space group P3121 and in both cases the asymmetric unit was composed of one molecule of the SH3-APP12 complex. The crystals of the Thr98Glu mutant in complex with the VSL12 peptide (VSLARRPLPLP) belonged to the trigonal space group P3221 and the asymmetric unit was also composed of a single molecule of the SH3-VSL12 complex.

An N-terminally truncated mutant of human chemokine CXCL14 has biological activity.

Chemokines are members of the superfamily of cytokines involved in: (i) cell migration to sites of infection; or (ii) cellular stress during an immune response. Human CXCL14/BRAK is a monocyte-selective chemokine expressed in all normal tissues, but is also involved in the development of several cancers. We describe the expression, structural characterization and biological activity of an N-terminal truncated mutant of CXCL14, ΔCXCL14, where the first eleven residues and the two disulphide bridges were removed.

pH-dependent structural conformations of B-phycoerythrin from Porphyridium cruentum.

B-phycoerythrin from the red alga Porphyridium cruentum was crystallized using the technique of capillary counter-diffusion. Crystals belonging to the space group R3 with almost identical unit cell constants and diffracting to 1.85 and 1.

Biophysical characterization of the isolated C-terminal region of the transient receptor potential vanilloid 1.

Transient receptor potential (TRP) proteins are sensory-related cation channels. TRPV subfamily responds to vanilloids, generating a Ca(2+) current. TRPV1, a thermal-sensitive non-selective ion channel, possesses six transmembrane helices and the intracellular N- and C-terminal domains.