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James C Hu

Publications and source records attributed to James C Hu.

5 recordsLinked to original sources
PubMed2005

Assessing methods for identifying pair-wise atomic contacts across binding interfaces.

An essential step in understanding the molecular basis of protein-protein interactions is the accurate identification of inter-protein contacts. We evaluate a number of common methods used in analyzing protein-protein interfaces: a Voronoi polyhedra-based approach, changes in solvent accessible surface area (DeltaSASA) and various radial cutoffs (closest atom, Cbeta, and centroid). First, we compared the Voronoi polyhedra-based analysis to the DeltaSASA and show that using Voronoi polyhedra finds knob-in-hole contacts. To assess the accuracy between the Voronoi polyhedra-based approach and the various radial cutoff methods, two sets of data were used: a small set of 75 experimental mutants and a larger one of 592 structures of protein-protein interfaces. In an assessment using the small set, the Voronoi polyhedra-based methods, a solvent accessible surface area method, and the closest atom radial method identified 100% of the direct contacts defined by mutagenesis data, but only the Voronoi polyhedra-based method found no false positives. The other radial methods were not able to find all of the direct contacts even using a cutoff of 9A. With the larger set of structures, we compared the overall number contacts using the Voronoi polyhedra-based method as a standard. All the radial methods using a 6-A cutoff identified more interactions, but these putative contacts included many false positives as well as missed many false negatives. While radial cutoffs are quicker to calculate as well as to implement, this result highlights why radial cutoff methods do not have the proper resolution to detail the non-homogeneous packing within protein interfaces, and suggests an inappropriate bias in pair-wise contact potentials. Of the radial cutoff methods, using the closest atom approach exhibits the best approximation to the more intensive Voronoi calculation. Our version of the Voronoi polyhedra-based method QContacts is available at .

Databases, Protein↗
PubMed2004

Identification and mapping of self-assembling protein domains encoded by the Escherichia coli K-12 genome by use of lambda repressor fusions.

Self-assembling proteins and protein fragments encoded by the Escherichia coli genome were identified from E. coli K-12 strain MG1655. Libraries of random DNA fragments cloned into a series of lambda repressor fusion vectors were subjected to selection for immunity to infection by phage lambda. Survivors were identified by sequencing the ends of the inserts, and the fused protein sequence was inferred from the known genomic sequence. Four hundred sixty-three nonredundant open reading frame-encoded interacting sequence tags (ISTs) were recovered from sequencing 2,089 candidates. These ISTs, which range from 16 to 794 amino acids in length, were clustered into families of overlapping fragments, identifying potential homotypic interactions encoded by 232 E. coli genes. Repressor fusions identified ISTs from genes in every protein-based functional category, but membrane proteins were underrepresented. The IST-containing genes were enriched for regulatory proteins and for proteins that form higher-order oligomers. Forty-eight (20.7%) homotypic proteins identified by ISTs are predicted to contain coiled coils. Although most of the IST-containing genes are identifiably related to proteins in other bacterial genomes, more than half of the ISTs do not have identifiable homologs in the Protein Data Bank, suggesting that they may include many novel structures. The data are available online at http://oligomers.tamu.edu/.

Artificial Gene Fusion↗
PubMed2003

Proteome analysis of Escherichia coli K-12 by two-dimensional native-state chromatography and MALDI-MS.

To identify proteins expressed in Escherichia coli K-12 MG1655 during exponential growth in defined medium, we separated soluble proteins of E. coli over two dimensions of native-state high-performance liquid chromatography, and examined the components of the protein mixtures in each of 380 fractions by peptide mass fingerprinting. To date, we have identified the products of 310 genes covering a wide range of cellular functions. Validation of protein assignments was made by comparing the assignments of proteins to specific first-dimension fractions to proteins visualized by two-dimensional gel electrophoresis. Co-fractionation of proteins suggests the possible identities of components of multiprotein complexes. This approach yields high-throughput gel-independent identification of proteins. It can also be used to assign identities to spots visualized by two-dimensional gels, and should be useful to evaluate differences in expressed proteome content and protein complexes among strains or between different physiological states.

Chromatography, High Pressure Liquid↗
PubMed2002

Isolation and mapping of self-assembling protein domains encoded by the Saccharomyces cerevisiae genome using lambda repressor fusions.

Understanding how proteins are able to form stable complexes is of fundamental interest from the perspective of protein structure and function. Here we show that lambda repressor fusions can be used to identify and characterize homotypic interaction domains encoded by the genome of Saccharomyces cerevisiae, using a selection for polypeptides that can drive the assembly of the DNA binding domain of bacteriophage lambda repressor. Three high complexity libraries were constructed by cloning random fragments of S. cerevisiae DNA as lambda repressor fusions. Repressor fusions encoding homotypic interactions were recovered, identifying oligomerization units in 35 yeast proteins. Seventeen of these interaction domains have not been previously reported, while the other 18 represent homotypic interactions that have been characterized at varying levels of detail. The novel interactions include several predicted coiled-coils as well as domains of unknown structure. With the availability of genomic sequences it should be possible to apply this approach, which provides information about protein-protein interactions that is complementary to that obtained from yeast two-hybrid screens, on a genome-wide scale in yeast or other organisms where large-scale protein-protein interaction data is not available.

Amino Acid Sequence↗