Biomedical subjects

Catherine H Schein

Publications and source records attributed to Catherine H Schein.

24 records · Page 2Linked to original sources

PubMed2003

SDAP: database and computational tools for allergenic proteins.

SDAP (Structural Database of Allergenic Proteins) is a web server that provides rapid, cross-referenced access to the sequences, structures and IgE epitopes of allergenic proteins. The SDAP core is a series of CGI scripts that process the user queries, interrogate the database, perform various computations related to protein allergenic determinants and prepare the output HTML pages. The database component of SDAP contains information about the allergen name, source, sequence, structure, IgE epitopes and literature references and easy links to the major protein (PDB, SWISS-PROT/TrEMBL, PIR-ALN, NCBI Taxonomy Browser) and literature (PubMed, MEDLINE) on-line servers. The computational component in SDAP uses an original algorithm based on conserved properties of amino acid side chains to identify regions of known allergens similar to user-supplied peptides or selected from the SDAP database of IgE epitopes. This and other bioinformatics tools can be used to rapidly determine potential cross-reactivities between allergens and to screen novel proteins for the presence of IgE epitopes they may share with known allergens. SDAP is available via the World Wide Web at http://fermi.utmb.edu/SDAP/.

Allergens↗

PubMed2003

Major linear IgE epitopes of mountain cedar pollen allergen Jun a 1 map to the pectate lyase catalytic site.

Resolution of the 3D structures and IgE epitopes of allergens may identify common or conserved features of allergens. Jun a 1, the predominant allergen in mountain cedar pollen, was chosen as a model for identifying common structural and functional features among a group of plant allergens. In this study, synthetic, overlapping peptides of Jun a 1 and sera from patients allergic to mountain cedar pollen were used to identify linear epitopes. A 3D model of Jun a 1 was produced using the Bacillus subtiles pectate lyase (PL) as a template and validated with biophysical measurements. This allowed mappings of four IgE binding sites on Jun a 1. Two of the epitopes mapped to turns or loops on the surface of the model structure. The other two epitopes mapped to the beta-sheet region, homologous to the catalytic site of PL. This region of Jun a 1 is highly conserved in the group 1 allergens from other cedar trees as well as microbial PLs. The finding that two out of three major IgE epitopes map to highly conserved catalytic regions of group 1 cedar allergens may help to explain the high degree of cross-reactivity between cedar pollen allergens and might represent a pattern of reactivity common to other allergens with catalytic activity.

Allergens↗

PubMed2002

Total sequence decomposition distinguishes functional modules, "molegos" in apurinic/apyrimidinic endonucleases.

BACKGROUND: Total sequence decomposition, using the web-based MASIA tool, identifies areas of conservation in aligned protein sequences. By structurally annotating these motifs, the sequence can be parsed into individual building blocks, molecular legos ("molegos"), that can eventually be related to function. Here, the approach is applied to the apurinic/apyrimidinic endonuclease (APE) DNA repair proteins, essential enzymes that have been highly conserved throughout evolution. The APEs, DNase-1 and inositol 5'-polyphosphate phosphatases (IPP) form a superfamily that catalyze metal ion based phosphorolysis, but recognize different substrates. RESULTS: MASIA decomposition of APE yielded 12 sequence motifs, 10 of which are also structurally conserved within the family and are designated as molegos. The 12 motifs include all the residues known to be essential for DNA cleavage by APE. Five of these molegos are sequentially and structurally conserved in DNase-1 and the IPP family. Correcting the sequence alignment to match the residues at the ends of two of the molegos that are absolutely conserved in each of the three families greatly improved the local structural alignment of APEs, DNase-1 and synaptojanin. Comparing substrate/product binding of molegos common to DNase-1 showed that those distinctive for APEs are not directly involved in cleavage, but establish protein-DNA interactions 3' to the abasic site. These additional bonds enhance both specific binding to damaged DNA and the processivity of APE1. CONCLUSION: A modular approach can improve structurally predictive alignments of homologous proteins with low sequence identity and reveal residues peripheral to the traditional "active site" that control the specificity of enzymatic activity.

Amino Acid Motifs↗

PubMed2002

Membrane-protein interactions contribute to efficient 27-hydroxylation of cholesterol by mitochondrial cytochrome P450 27A1.

Mitochondrial cytochrome P450 27A1 (P450 27A1) catalyzes 27-hydroxylation of cholesterol, the first step in the alternative bile acid biosynthetic pathway. Although several crystal structures of P450s are known, no structural information is available for the mammalian, membrane-bound enzymes involved in the removal of cholesterol from the body. We prepared a three-dimensional model of P450 27A1 based on the structure of P450 BM-3. Conservative and non-conservative mutations were introduced at hydrophobic and positively charged residues in the putative F-G loop and the adjacent helix G (positions 219-237). Subcellular distribution of the mutant P450s expressed in Escherichia coli was used as a measure of membrane-protein interactions. Conservative substitutions of residues located on the surface, according to our model, L219V, L219I, Y220F, F223Y, L224I, R229K, V231L, F234Y, K236R, and R237K, weakened the association of the mutant P450s with the membrane and led to the appearance of up to 21% of P450 27A1 in the bacterial cytosol. It is likely that the mutated side chains are involved in binding to membrane phospholipids. Substitutions in the F-G loop did not significantly affect the K(m) value for cholesterol hydroxylation. However, non-conservative mutants, L219N, Y220A, Y220S, F223A, K226R, and R229A, had significantly impaired catalytic properties, indicating strict requirements for the size and polarity of the side chains at these positions for the catalysis. The results provide insight into the membrane topology of mitochondrial P450s and indicate the importance of membrane-protein interactions in the efficiency of reactions catalyzed by P450 27A1.

Amino Acid Sequence↗

PubMed2002

Data mining of sequences and 3D structures of allergenic proteins.

MOTIVATION: Many sequences, and in some cases structures, of proteins that induce an allergic response in atopic individuals have been determined in recent years. This data indicates that allergens, regardless of source, fall into discreet protein families. Similarities in the sequence may explain clinically observed cross-reactivities between different biological triggers. However, previously available allergy databases group allergens according to their biological sources, or observed clinical cross-reactivities, without providing data about the proteins. A computer-aided data mining system is needed to compare the sequential and structural details of known allergens. This information will aid in predicting allergenic cross-responses and eventually in determining possible common characteristics of IgE recognition. RESULTS: The new web-based Structural Database of Allergenic Proteins (SDAP) permits the user to quickly compare the sequence and structure of allergenic proteins. Data from literature sources and previously existing lists of allergens are combined in a MySQL interactive database with a wide selection of bioinformatics applications. SDAP can be used to rapidly determine the relationship between allergens and to screen novel proteins for the presence of IgE or T-cell epitopes they may share with known allergens. Further, our novel similarity search method, based on five dimensional descriptors of amino acid properties, can be used to scan the SDAP entries with a peptide sequence. For example, when a known IgE binding epitope from shrimp tropomyosin was used as a query, the method rapidly identified a similar sequence in known shellfish and insect allergens. This prediction of cross-reactivity between allergens is consistent with clinical observations. AVAILABILITY: SDAP is available on the web at http://fermi.utmb.edu/SDAP/index.html

Allergens↗

PubMed2002

The shape of the messenger: using protein structure information to design novel cytokine-based therapeutics.

The cloning and mass production of recombinant cytokine proteins opened a new world of treatment possibilities. While some cytokines, including several haematopoietic factors and interferons, are now used routinely in the clinic, there are still many problems with side effects. These are due to the many different activities of cytokines on different cell populations. In some cases, activities responsible for side effects have been attributed to discreet areas of the proteins and "structure driven design" can be used to generate novel proteins with better clinical profile. In other cases, structural alterations can enhance activity by increasing serum half-life. This review summarizes the structures of cytokines and their receptor complexes deposited in the Protein Data Base (PDB) and introduces the other articles in this issue on structure-driven design of cytokines for therapy. Cytokines fall into only a few structural classifications. Most of the growth regulatory cytokines including serum factors, growth hormone, haematopoietic growth factors, colony stimulating factors, erythropoietin, IL-3, IL-2 and interferons, are four or five helix bundles. Factors which primarily induce inflammatory responses, including TNF, lymphotoxin and IL-1, form beta-barrel structures that resemble the FGF family. Chemokines and factors that regulate multicellular responses, such as macrophage migration, neutrophil invasion and chemotaxis, have similar structures, classified as alpha + beta. One biological paradox is that many cytokines that vary greatly in function have a similar structure and share receptors. However, homologous cytokines may differ considerably in their mode of interaction with a shared receptor. A few structures for the extracellular regions of cytokine receptors are known, in several cases complexed with their biological target. These structures, coupled with structural alignment of families, indicate areas that control binding to receptors, as opposed to specific areas responsible for the specific activities of this diverse group of proteins. Methods to use cytokine structure to derive better therapeutics are summarized.

Amino Acid Sequence↗