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Rosalind Kim

Publications and source records attributed to Rosalind Kim.

At least 37 records · Page 2Linked to original sources
PubMed2005

Structural genomics of minimal organisms and protein fold space.

The initial aim of the Berkeley Structural Genomics Center is to obtain a near-complete structural complement of two minimal organisms, closely related pathogens Mycoplasma genitalium and M. pneumoniae. The former has fewer than 500 genes and the latter fewer than 700 genes. To achieve this goal, the current protein targets have been selected starting with those predicted to be most tractable and likely to yield new structural and functional information. During the past 3 years, the semi-automated structural genomics pipeline has been set up from cloning, expression, purification, and ultimately to structural determination. The results from the pipeline substantially increased the coverage of the protein fold space of M. pneumoniae and M. genitalium. Furthermore, about 1/2 of the structures of 'unique' protein sequences revealed new and novel folds, and over 2/3 of the structures of previously annotated 'hypothetical proteins' inferred their molecular functions.

Bacterial Proteins↗
PubMed2005

On-column protein refolding for crystallization.

One major bottleneck in protein production in Escherichia coli for structural genomics projects is the formation of insoluble protein aggregates (inclusion bodies). The efficient refolding of proteins from inclusion bodies is becoming an important tool that can provide soluble native proteins for structural and functional studies. Here we report an on-column refolding method established at the Berkeley Structural Genomics Center (BSGC). Our method is a combination of an 'artificial chaperone-assisted refolding' method previously proposed and affinity chromatography to take advantage of a chromatographic step: less time-consuming, no filtration or concentration, with the additional benefit of protein purification. It can be easily automated and formatted for high-throughput process.

Chromatography, Affinity↗
PubMed2005

Crystal structure of the "PhoU-like" phosphate uptake regulator from Aquifex aeolicus.

The phoU gene of Aquifex aeolicus encodes a protein called PHOU_AQUAE with sequence similarity to the PhoU protein of Escherichia coli. Despite the fact that there is a large number of family members (more than 300) attributed to almost all known bacteria and despite PHOU_AQUAE's association with the regulation of genes for phosphate metabolism, the nature of its regulatory function is not well understood. Nearly one-half of these PhoU-like proteins, including both PHOU_AQUAE and the one from E. coli, form a subfamily with an apparent dimer structure of two PhoU domains on the basis of their amino acid sequence. The crystal structure of PHOU_AQUAE (a 221-amino-acid protein) reveals two similar coiled-coil PhoU domains, each forming a three-helix bundle. The structures of PHOU_AQUAE proteins from both a soluble fraction and refolded inclusion bodies (at resolutions of 2.8 and 3.2A, respectively) showed no significant differences. The folds of the PhoU domain and Bag domains (for a class of cofactors of the eukaryotic chaperone Hsp70 family) are similar. Accordingly, we propose that gene regulation by PhoU may occur by association of PHOU_AQUAE with the ATPase domain of the histidine kinase PhoR, promoting release of its substrate PhoB. Other proteins that share the PhoU domain fold include the coiled-coil domains of the STAT protein, the ribosome-recycling factor, and structural proteins like spectrin.

Amino Acid Sequence↗
PubMed2004

Crystal structure of YjeQ from Thermotoga maritima contains a circularly permuted GTPase domain.

We have determined the crystal structure of the GDP complex of the YjeQ protein from Thermotoga maritima (TmYjeQ), a member of the YjeQ GTPase subfamaily. TmYjeQ, a homologue of Escherichia coli YjeQ, which is known to bind to the ribosome, is composed of three domains: an N-terminal oligonucleotide/oligosaccharide-binding fold domain, a central GTPase domain, and a C-terminal zinc-finger domain. The crystal structure of TmYjeQ reveals two interesting domains: a circularly permutated GTPase domain and an unusual zinc-finger domain. The binding mode of GDP in the GTPase domain of TmYjeQ is similar to those of GDP or GTP analogs in ras proteins, a prototype GTPase. The N-terminal oligonucleotide/oligosaccharide-binding fold domain, together with the GTPase domain, forms the extended RNA-binding site. The C-terminal domain has an unusual zinc-finger motif composed of Cys-250, Cys-255, Cys-263, and His-257, with a remote structural similarity to a portion of a DNA-repair protein, rad51 fragment. The overall structural features of TmYjeQ make it a good candidate for an RNA-binding protein, which is consistent with the biochemical data of the YjeQ subfamily in binding to the ribosome.

Amino Acid Sequence↗
PubMed2004

Optimum solubility (OS) screening: an efficient method to optimize buffer conditions for homogeneity and crystallization of proteins.

One of the most critical steps in the preparation of protein samples for structural studies by X-ray crystallography is to obtain biochemically pure and conformationally homogenous protein samples. Very often, the purified sample does not meet these qualifications and therefore does not crystallize. A screening method, Optimum Solubility Screen, has been developed that consists of two steps. The first step selects a better buffer than that used during purification. 24 different buffers ranging from pH 3 to pH 10 are screened using a vapor-diffusion method and very small amounts of protein. The solubility of the protein is first determined by visual examination using a light microscope and those drops that remain clear after 24 h are further evaluated using dynamic light scattering. If the results from the first step are still not satisfactory, a second step explores a variety of chemical additives in order to improve the monodispersity of the protein sample. In 64% of the cases, crystallization was successful from proteins that had initially shown high levels of aggregation. This screen can be configured to perform in an automated high-throughput mode and can be expanded for additional buffers and additives.

Buffers↗
PubMed2004

Structural analyses of peptide release factor 1 from Thermotoga maritima reveal domain flexibility required for its interaction with the ribosome.

We have determined the crystal structure of peptide chain release factor 1 (RF1) from Thermotoga maritima (gi 4981173) at 2.65 Angstrom resolution by selenomethionine single-wavelength anomalous dispersion (SAD) techniques. RF1 is a protein that recognizes stop codons and promotes the release of a nascent polypeptide from tRNA on the ribosome. Selenomethionine-labeled RF1 crystallized in space group P2(1) with three monomers per asymmetric unit. It has approximate dimensions of 75 Angstrom x 70 Angstrom x 45 Angstrom and is composed of four domains. The overall fold of each RF1 domain shows almost the same topology with Escherichia coli RF2, except that the RF1 N-terminal domain is shorter and the C-terminal domain is longer than that of RF2. The N-terminal domain of RF1 indicates a rigid-body movement relative to that of RF2 with an angle of approximately 90 degrees. Including these features, RF1 has a tripeptide anticodon PVT motif instead of the SPF motif of RF2, which confers the specificity towards the stop codons. The analyses of three molecules in the asymmetric unit and comparison with RF2 revealed the presence of dynamic movement of domains I and III, which are anchored to the central domain by hinge loops. The crystal structure of RF1 elucidates the intrinsic property of this family of having large domain movements for proper function with the ribosome.

Amino Acid Sequence↗
PubMed2004

Structure of the putative DNA-binding protein SP_1288 from Streptococcus pyogenes.

The crystal structure of the putative DNA-binding protein SP_1288 (gi/15675166, also listed as gi/28895954) from Streptococcus pyogenes has been determined by X-ray crystallography to a resolution of 2.3 A using anomalous diffraction data at the Se peak wavelength. SP_1288 belongs to a family of proteins whose cellular function is associated with the signal recognition particle; no structural information has been available until now about the members of the family. Crystallographic analysis revealed that the overall fold of SP_1288 consists exclusively of alpha-helices and that 75% of the structure has good similarity to domain 4 of the sigma subunit of RNA polymerase. This suggests its possible involvement in the biochemical function of transcription initiation, which includes interaction with DNA.

Amino Acid Sequence↗
PubMed2004

Crystal structure of a protein associated with cell division from Mycoplasma pneumoniae (GI: 13508053): a novel fold with a conserved sequence motif.

UPF0040 is a family of proteins implicated in a cellular function of bacteria cell division. There is no structure information available on protein of this family. We have determined the crystal structure of a protein from Mycoplasma pneumoniae that belongs to this family using X-ray crystallography. Structural homology search reveals that this protein has a novel fold with no significant similarity to any proteins of known three-dimensional structure. The crystal structures of the protein in three different crystal forms reveal that the protein exists as a ring of octamer. The conserved protein residues, including a highly conserved DXXXR motif, are examined on the basis of crystal structure.

Amino Acid Motifs↗
PubMed2004

Structural and functional characterization of a novel phosphodiesterase from Methanococcus jannaschii.

Methanococcus jannaschii MJ0936 is a hypothetical protein of unknown function with over 50 homologs found in many bacteria and Archaea. To help define the molecular (biochemical and biophysical) function of MJ0936, we determined its crystal structure at 2.4-A resolution and performed a series of biochemical screens for catalytic activity. The overall fold of this single domain protein consists of a four-layered structure formed by two beta-sheets flanked by alpha-helices on both sides. The crystal structure suggested its biochemical function to be a nuclease, phosphatase, or nucleotidase, with a requirement for some metal ions. Crystallization in the presence of Ni(2+) or Mn(2+) produced a protein containing a binuclear metal center in the putative active site formed by a cluster of conserved residues. Analysis of MJ0936 against a panel of general enzymatic assays revealed catalytic activity toward bis-p-nitrophenyl phosphate, an indicator substrate for phosphodiesterases and nucleases. Significant activity was also found with two other phosphodiesterase substrates, thymidine 5'-monophosphate p-nitrophenyl ester and p-nitrophenylphosphorylcholine, but no activity was found for cAMP or cGMP. Phosphodiesterase activity of MJ0936 had an absolute requirement for divalent metal ions with Ni(2+) and Mn(2+) being most effective. Thus, our structural and enzymatic studies have identified the biochemical function of MJ0936 as that of a novel phosphodiesterase.

Amino Acid Sequence↗
PubMed2004

Structure of OsmC from Escherichia coli: a salt-shock-induced protein.

The crystal structure of an osmotically inducible protein (OsmC) from Escherichia coli has been determined at 2.4 A resolution. OsmC is a representative protein of the OsmC sequence family, which is composed of three sequence subfamilies. The structure of OsmC provides a view of a salt-shock-induced protein. Two identical monomers form a cylindrically shaped dimer in which six helices are located on the inside and two six-stranded beta-sheets wrap around these helices. Structural comparison suggests that the OsmC sequence family has a peroxiredoxin function and has a unique structure compared with other peroxiredoxin families. A detailed analysis of structures and sequence comparisons in the OsmC sequence family revealed that each subfamily has unique motifs. In addition, the molecular function of the OsmC sequence family is discussed based on structural comparisons among the subfamily members.

Amino Acid Sequence↗
PubMed2004

An automated small-scale protein expression and purification screening provides beneficial information for protein production.

One of the first key steps in structural genomics is high-throughput expression and rapid screening to select highly soluble proteins, the preferred candidates for crystal production. Here we describe the methodology used at the Berkeley Structural Genomics Center (BSGC) for automated parallel expression and small-scale purification of fusion proteins using a 96-well format. Our robotic method includes cell lysis, soluble fraction separation and purification with affinity resins. For detection of His-tagged proteins in the soluble fractions and after affinity resin elution, a dot-blot procedure with an anti-His-antibody is used. The expression level and molecular mass of recombinant proteins are checked by SDS-PAGE. With this approach, we are able to obtain beneficial information to be used for large-scale protein expression and purification.

Automation↗
PubMed2004

Using an Escherichia coli cell-free extract to screen for soluble expression of recombinant proteins.

For structural and functional genomics programs, new high-throughput methods to characterize well-expressing and highly soluble proteins are essential. A faster and more convenient approach to screen expression conditions of recombinant proteins compared to classical in vivo systems is the Escherichia coli cell-free expression system. Here, we describe a rapid procedure to screen for expression and solubility of recombinant proteins using an E. coli cell-free extract. The results presented cover 24 open reading frames of unknown function from different micro-organisms. In order to screen different variables that may interfere with solubility, we expressed the recombinant proteins with a histidine6 tag, either N-terminal or C-terminal at two temperatures (25 degrees C and 30 degrees C). The identification of recombinant proteins is performed by the dot blot procedure using an anti-histidine tag antibody. We designed a rapid method that allows the characterization of soluble candidates from a large number of genes or from a large number of variants that is highly compatible with structural genomics expectations.

DNA, Recombinant↗
PubMed2003

Crystal structure of NusA from Thermotoga maritima and functional implication of the N-terminal domain.

We report the crystal structure of N-utilizing substance A protein (NusA) from Thermotoga maritima (TmNusA), a protein involved in transcriptional pausing, termination, and antitermination. TmNusA has an elongated rod-shaped structure consisting of an N-terminal domain (NTD, residues 1-132) and three RNA binding domains (RBD). The NTD consists of two subdomains, the globular head and the helical body domains, that comprise a unique three-dimensional structure that may be important for interacting with RNA polymerase. The globular head domain possesses a high content of negatively charged residues that may interact with the positively charged flaplike domain of RNA polymerase. The helical body domain is composed of a three-helix bundle that forms a hydrophobic core with the aid of two neighboring beta-strands. This domain shows structural similarity with one of the helical domains of sigma(70) factor from Escherichia coli. One side of the molecular surface shows positive electrostatic potential suitable for nonspecific RNA interaction. The RBD is composed of one S1 domain and two K-homology (KH) domains forming an elongated RNA binding surface. Structural comparison between TmNusA and Mycobacterium tuberculosis NusA reveals a possible hinge motion between NTD and RBD. In addition, a functional implication of the NTD in its interaction with RNA polymerase is discussed.

Amino Acid Sequence↗