Jason W. Schmidberger

The Crystal Structure of DehI Reveals a New α-Haloacid Dehalogenase Fold and Active-Site Mechanism

Haloacid dehalogenases catalyse the removal of halides from organic haloacids and are of interest for bioremediation and for their potential use in the synthesis of industrial chemicals. We present the crystal structure of the homodimer DehI from Pseudomonas putida strain PP3, the first structure of a group I alpha-haloacid dehalogenase that can process both L- and D-substrates. The structure shows that the DehI monomer consists of two domains of approximately 130 amino acids that have approximately 16% sequence identity yet adopt virtually identical and unique folds that form a pseudo-dimer. Analysis of the active site reveals the likely binding mode of both L- and D-substrates with respect to key catalytic residues. Asp189 is predicted to activate a water molecule for nucleophilic attack of the substrate chiral centre resulting in an inversion of configuration of either l- or d-substrates in contrast to D-only enzymes. These details will assist with future bioengineering of dehalogenases.

Federated repositories of X‐ray diffraction images

There is a pressing need for the archiving and curation of raw X-ray diffraction data. This information is critical for validation, methods development and improvement of archived structures. However, the relatively large size of these data sets has presented challenges for storage in a single worldwide repository such as the Protein Data Bank archive. This problem can be avoided by using a federated approach, where each institution utilizes its institutional repository for storage, with a discovery service overlaid. Institutional repositories are relatively stable and adequately funded, ensuring persistence. Here, a simple repository solution is described, utilizing Fedora open-source database software and data-annotation and deposition tools that can be deployed at any site cheaply and easily. Data sets and associated metadata from federated repositories are given a unique and persistent handle, providing a simple mechanism for search and retrieval via web interfaces. In addition to ensuring that valuable data is not lost, the provision of raw data has several uses for the crystallographic community. Most importantly, structure determination can only be truly repeated or verified when the raw data are available. Moreover, the availability of raw data is extremely useful for the development of improved methods of image analysis and data processing.

Grb7 SH2 domain structure and interactions with a cyclic peptide inhibitor of cancer cell migration and proliferation.

BackgroundHuman g rowth factor r eceptor b ound protein 7 (Grb7) is an adapter protein that mediates the coupling of tyrosine kinases with their downstream signaling pathways. Grb7 is frequently overexpressed in invasive and metastatic human cancers and is implicated in cancer progression via its interaction with the ErbB2 receptor and focal adhesion kinase (FAK) that play critical roles in cell proliferation and migration. It is thus a prime target for the development of novel anti-cancer therapies. Recently, an inhibitory peptide (G7-18NATE) has been developed which binds specifically to the Grb7 SH2 domain and is able to attenuate cancer cell proliferation and migration in various cancer cell lines.ResultsAs a first step towards understanding how Grb7 may be inhibited by G7-18NATE, we solved the crystal structure of the Grb7 SH2 domain to 2.1 Å resolution. We describe the details of the peptide binding site underlying target specificity, as well as the dimer interface of Grb 7 SH2. Dimer formation of Grb7 was determined to be in the μM range using analytical ultracentrifugation for both full-length Grb7 and the SH2 domain alone, suggesting the SH2 domain forms the basis of a physiological dimer. ITC measurements of the interaction of the G7-18NATE peptide with the Grb7 SH2 domain revealed that it binds with a binding affinity of Kd = ~35.7 μM and NMR spectroscopy titration experiments revealed that peptide binding causes perturbations to both the ligand binding surface of the Grb7 SH2 domain as well as to the dimer interface, suggesting that dimerisation of Grb7 is impacted on by peptide binding.ConclusionTogether the data allow us to propose a model of the Grb7 SH2 domain/G7-18NATE interaction and to rationalize the basis for the observed binding specificity and affinity. We propose that the current study will assist with the development of second generation Grb7 SH2 domain inhibitors, potentially leading to novel inhibitors of cancer cell migration and invasion.

The AEROPATH project targeting Pseudomonas aeruginosa: crystallographic studies for assessment of potential targets in early-stage drug discovery.

A focused strategy has been directed towards the structural characterization of selected proteins from the bacterial pathogen P. aeruginosa. The objective is to exploit the resulting structural data, in combination with ligand-binding studies, and to assess the potential of these proteins for early-stage antimicrobial drug discovery.

Refolding Your Protein with a Little Help from REFOLD

The expression and harvesting of proteins from insoluble inclusion bodies by solubilization and refolding is a technique commonly used in the production of recombinant proteins. Despite the importance of refolding, publications in the literature are essentially ad hoc reports consisting of a dazzling array of experimental protocols and a diverse collection of buffer cocktails. For the protein scientists, using this information to refold their protein of interest presents enormous challenges. Here, we describe some of the practical considerations in refolding and present several standard protocols. Further, we describe how refolding procedures can be designed and modified using the information in the REFOLD database (http://refold.med.monash.edu.au), a freely available, open repository for protocols describing the refolding and purification of recombinant proteins.

MrGrid: a portable grid based molecular replacement pipeline.

Background The crystallographic determination of protein structures can be computationally demanding and for difficult cases can benefit from user-friendly interfaces to high-performance computing resources. Molecular replacement (MR) is a popular protein crystallographic technique that exploits the structural similarity between proteins that share some sequence similarity. But the need to trial permutations of search models, space group symmetries and other parameters makes MR time- and labour-intensive. However, MR calculations are embarrassingly parallel and thus ideally suited to distributed computing. In order to address this problem we have developed MrGrid, web-based software that allows multiple MR calculations to be executed across a grid of networked computers, allowing high-throughput MR. Methodology/Principal Findings MrGrid is a portable web based application written in Java/JSP and Ruby, and taking advantage of Apple Xgrid technology. Designed to interface with a user defined Xgrid resource the package manages the distribution of multiple MR runs to the available nodes on the Xgrid. We evaluated MrGrid using 10 different protein test cases on a network of 13 computers, and achieved an average speed up factor of 5.69. Conclusions MrGrid enables the user to retrieve and manage the results of tens to hundreds of MR calculations quickly and via a single web interface, as well as broadening the range of strategies that can be attempted. This high-throughput approach allows parameter sweeps to be performed in parallel, improving the chances of MR success.

The MTA1 subunit of the nucleosome remodeling and deacetylase complex can recruit two copies of RBBP4/7

The nucleosome remodeling and deacetylase (NuRD) complex remodels the genome in the context of both gene transcription and DNA damage repair. It is essential for normal development and is distributed across multiple tissues in organisms ranging from mammals to nematode worms. In common with other chromatin‐remodeling complexes, however, its molecular mechanism of action is not well understood and only limited structural information is available to show how the complex is assembled. As a step towards understanding the structure of the NuRD complex, we have characterized the interaction between two subunits: the metastasis associated protein MTA1 and the histone‐binding protein RBBP4. We show that MTA1 can bind to two molecules of RBBP4 and present negative stain electron microscopy and chemical crosslinking data that allow us to build a low‐resolution model of an MTA1‐(RBBP4)2 subcomplex. These data build on our understanding of NuRD complex structure and move us closer towards an understanding of the biochemical basis for the activity of this complex.

Structural characterization of substrate and inhibitor binding to farnesyl pyrophosphate synthase from Pseudomonas aeruginosa

The crystal structures of farnesyl diphosphate synthase from the pathogen Pseudomonas aeruginosa in complex with substrates and inhibitors have been determined. The study reveals the presence of an allosteric binding pocket also in bacterial enzymes that, similar to the human enzyme, could be the target for the design of specific and potent inhibitors.

Refinement of the subunit interaction network within the nucleosome remodelling and deacetylase (NuRD) complex

The nucleosome remodelling and deacetylase (NuRD) complex is essential for the development of complex animals. NuRD has roles in regulating gene expression and repairing damaged DNA. The complex comprises at least six proteins with two or more paralogues of each protein routinely identified when the complex is purified from cell extracts. To understand the structure and function of NuRD, a map of direct subunit interactions is needed. Dozens of published studies have attempted to define direct inter‐subunit connectivities. We propose that conclusions reported in many such studies are in fact ambiguous for one of several reasons. First, the expression of many NuRD subunits in bacteria is unlikely to lead to folded, active protein. Second, interaction studies carried out in cells that contain endogenous NuRD complex can lead to false positives through bridging of target proteins by endogenous components. Combining existing information on NuRD structure with a protocol designed to minimize false positives, we report a conservative and robust interaction map for the NuRD complex. We also suggest a 3D model of the complex that brings together the existing data on the complex. The issues and strategies discussed herein are also applicable to the analysis of a wide range of multi‐subunit complexes.

Purification, crystallization and preliminary crystallographic analysis of DehI, a group I alpha-haloacid dehalogenase from Pseudomonas putida strain PP3.

Pseudomonas putida strain PP3 produces two dehalogenases, DehI and DehII, which belong to the group I and II alpha-haloacid dehalogenases, respectively. Group I dehalogenases catalyse the removal of halides from D-haloalkanoic acids and in some cases also the L-enantiomers, both substituted at their chiral centres. Studies of members of this group have resulted in the proposal of general catalytic mechanisms, although no structural information is available in order to better characterize their function. This work presents the initial stages of the structural investigation of the group I alpha-haloacid dehalogenase DehI. The DehI gene was cloned into a pET15b vector with an N-terminal His tag and expressed in Escherichia coli Nova Blue strain. Purified protein was crystallized in 25% PEG 3350, 0.4 M lithium sulfate and 0.1 M bis-tris buffer pH 6.0. The crystals were primitive monoclinic (space group P2(1)), with unit-cell parameters a = 68.32, b = 111.86, c = 75.13 A, alpha = 90, beta = 93.7, gamma = 90 degrees , and a complete native data set was collected. Molecular replacement is not an option for structure determination, so further experimental phasing methods will be necessary.