Remko Kuipers

Protein structure analysis of mutations causing inheritable diseases. An e-Science approach with life scientist friendly interfaces

BackgroundMany newly detected point mutations are located in protein-coding regions of the human genome. Knowledge of their effects on the proteins 3D structure provides insight into the proteins mechanism, can aid the design of further experiments, and eventually can lead to the development of new medicines and diagnostic tools.ResultsIn this article we describe HOPE, a fully automatic program that analyzes the structural and functional effects of point mutations. HOPE collects information from a wide range of information sources including calculations on the 3D coordinates of the protein by using WHAT IF Web services, sequence annotations from the UniProt database, and predictions by DAS services. Homology models are built with YASARA. Data is stored in a database and used in a decision scheme to identify the effects of a mutation on the proteins 3D structure and function. HOPE builds a report with text, figures, and animations that is easy to use and understandable for (bio)medical researchers.ConclusionsWe tested HOPE by comparing its output to the results of manually performed projects. In all straightforward cases HOPE performed similar to a trained bioinformatician. The use of 3D structures helps optimize the results in terms of reliability and details. HOPEs results are easy to understand and are presented in a way that is attractive for researchers without an extensive bioinformatics background.

The alpha/beta-hydrolase fold 3DM database (ABHDB) as a tool for protein engineering.

Aligning the haystack to expose the needle: The 3DM method was used to generate a comprehensive database of the a/s-hydrolase fold enzyme superfamily. This database facilitates the analysis of structure–function relationships and enables novel insights into this superfamily to be made. In addition high-quality libraries for protein engineering can be easily designed.

3DM: Systematic analysis of heterogeneous superfamily data to discover protein functionalities

Ten years of experience with molecular class–specific information systems (MCSIS) such as with the hand‐curated G protein–coupled receptor database (GPCRDB) or the semiautomatically generated nuclear receptor database has made clear that a wide variety of questions can be answered when protein‐related data from many different origins can be flexibly combined. MCSISes revolve around a multiple sequence alignment (MSA) that includes “all” available sequences from the entire superfamily, and it has been shown at many occasions that the quality of these alignments is the most crucial aspect of the MCSIS approach. We describe here a system called 3DM that can automatically build an entire MCSIS. 3DM bases the MSA on a multiple structure alignment, which implies that the availability of a large number of superfamily members with a known three‐dimensional structure is a requirement for 3DM to succeed well. Thirteen MCSISes were constructed and placed on the Internet for examination. These systems have been instrumental in a large series of research projects related to enzyme activity or the understanding and engineering of specificity, protein stability engineering, DNA‐diagnostics, drug design, and so forth. Proteins 2010.

Correlated mutation analyses on super‐family alignments reveal functionally important residues

Correlated mutation analyses (CMA) on multiple sequence alignments are widely used for the prediction of the function of amino acids. The accuracy of CMA‐based predictions is mainly determined by the number of sequences, by their evolutionary distances, and by the quality of the alignments. These criteria are best met in structure‐based sequence alignments of large super‐families. So far, CMA‐techniques have mainly been employed to study the receptor interactions. The present work shows how a novel CMA tool, called Comulator, can be used to determine networks of functionally related residues in enzymes. These analyses provide leads for protein engineering studies that are directed towards modification of enzyme specificity or activity. As proof of concept, Comulator has been applied to four enzyme super‐families: the isocitrate lyase/phoshoenol‐pyruvate mutase super‐family, the hexokinase super‐family, the RmlC‐like cupin super‐family, and the FAD‐linked oxidases super‐family. In each of those cases networks of functionally related residue positions were discovered that upon mutation influenced enzyme specificity and/or activity as predicted. We conclude that CMA is a powerful tool for redesigning enzyme activity and selectivity. Proteins 2009.

Increasing the thermostability of sucrose phosphorylase by a combination of sequence- and structure-based mutagenesis

Sucrose phosphorylase is a promising biocatalyst for the glycosylation of a wide variety of acceptor molecules, but its low thermostability is a serious drawback for industrial applications. In this work, the stability of the enzyme from Bifidobacterium adolescentis has been significantly improved by a combination of smart and rational mutagenesis. The former consists of substituting the most flexible residues with amino acids that occur more frequently at the corresponding positions in related sequences, while the latter is based on a careful inspection of the enzymes crystal structure to promote electrostatic interactions. In this way, a variant enzyme could be created that contains six mutations and whose half-life at the industrially relevant temperature of 60 °C has more than doubled compared with the wild-type enzyme. An increased stability in the presence of organic co-solvents could also be observed, although these effects were most noticeable at low temperatures.

Novel tools for extraction and validation of disease‐related mutations applied to fabry disease

Genetic disorders are often caused by nonsynonymous nucleotide changes in one or more genes associated with the disease. Specific amino acid changes, however, can lead to large variability of phenotypic expression. For many genetic disorders this results in an increasing amount of publications describing phenotype‐associated mutations in disorder‐related genes. Keeping up with this stream of publications is essential for molecular diagnostics and translational research purposes but often impossible due to time constraints: there are simply too many articles to read. To help solve this problem, we have created Mutator, an automated method to extract mutations from full‐text articles. Extracted mutations are crossreferenced to sequence data and a scoring method is applied to distinguish false‐positives. To analyze stored and new mutation data for their (potential) effect we have developed Validator, a Web‐based tool specifically designed for DNA diagnostics. Fabry disease, a monogenetic gene disorder of the GLA gene, was used as a test case. A structure‐based sequence alignment of the alpha‐amylase superfamily was used to validate results. We have compared our data with existing Fabry mutation data sets obtained from the HGMD and Swiss‐Prot databases. Compared to these data sets, Mutator extracted 30% additional mutations from the literature. Hum Mutat 31:1026–1032, 2010.

Structure and function of 2,3-dimethylmalate lyase, a PEP mutase/isocitrate lyase superfamily member.

The Aspergillus niger genome contains four genes that encode proteins exhibiting greater than 30% amino acid sequence identity to the confirmed oxaloacetate acetyl hydrolase (OAH), an enzyme that belongs to the phosphoenolpyruvate mutase/isocitrate lyase superfamily. Previous studies have shown that a mutant A. niger strain lacking the OAH gene does not produce oxalate. To identify the function of the protein sharing the highest amino acid sequence identity with the OAH (An07g08390, Swiss-Prot entry Q2L887, 57% identity), we produced the protein in Escherichia coli and purified it for structural and functional studies. A focused substrate screen was used to determine the catalytic function of An07g08390 as (2R,3S)-dimethylmalate lyase (DMML): k(cat)=19.2 s(-1) and K(m)=220 microM. DMML also possesses significant OAH activity (k(cat)=0.5 s(-1) and K(m) =220 microM). DNA array analysis showed that unlike the A. niger oah gene, the DMML encoding gene is subject to catabolite repression. DMML is a key enzyme in bacterial nicotinate catabolism, catalyzing the last of nine enzymatic steps. This pathway does not have a known fungal counterpart. BLAST analysis of the A. niger genome for the presence of a similar pathway revealed the presence of homologs to only some of the pathway enzymes. This and the finding that A. niger does not thrive on nicotinamide as a sole carbon source suggest that the fungal DMML functions in a presently unknown metabolic pathway. The crystal structure of A. niger DMML (in complex with Mg(2+) and in complex with Mg(2+) and a substrate analog: the gem-diol of 3,3-difluoro-oxaloacetate) was determined for the purpose of identifying structural determinants of substrate recognition and catalysis. Structure-guided site-directed mutants were prepared and evaluated to test the contributions made by key active-site residues. In this article, we report the results in the broader context of the lyase branch of the phosphoenolpyruvate mutase/isocitrate lyase superfamily to provide insight into the evolution of functional diversity.

CorNet: Assigning function to networks of co-evolving residues by automated literature mining

CorNet is a web-based tool for the analysis of co-evolving residue positions in protein super-family sequence alignments. CorNet projects external information such as mutation data extracted from literature on interactively displayed groups of co-evolving residue positions to shed light on the functions associated with these groups and the residues in them. We used CorNet to analyse six enzyme super-families and found that groups of strongly co-evolving residues tend to consist of residues involved in a same function such as activity, specificity, co-factor binding, or enantioselectivity. This finding allows to assign a function to residues for which no data is available yet in the literature. A mutant library was designed to mutate residues observed in a group of co-evolving residues predicted to be involved in enantioselectivity, but for which no literature data is available yet. The resulting set of mutations indeed showed many instances of increased enantioselectivity.

Common Pitfalls and Novel Opportunities for Predicting Variant Pathogenicity

The prediction of missense variant pathogenicity is normally performed using analyses of multiple sequence alignments optionally augmented with analyses of the (predicted) protein structure. The most straightforward way, though, is to search the literature to see whether this variant has already been described. Variant data from homologous proteins are also valuable because mutations in a homologous protein often have similar effects as mutations at the equivalent residues of the protein of interest. Transferring variant data seems trivial but is seriously hampered by the fact that homologous residue positions have different numbers in different species. This problem is even bigger when to proteins have such low sequence identities that they can no longer be aligned based on their sequences only and their structures need to be compared to align them accurately. The protein superfamily analysis software suite 3DM solves these problems, because 3DM is a system that combines high quality structure based multiple sequence alignments in which aligned residues have the same number, with all published mutant and variant data for human and all other species. We have used 3DM to analyze nine human proteins for which many disease-related variants are known. This study reveals that mutation data can be transferred even between very distant homologous proteins. Thus, protein superfamily information systems, such as 3DM, offer a wealth of unused information that can be used in the analysis of human variants.