A three-dimensional model of human organic anion transporter 1: aromatic amino acids required for substrate transport

Organic anion transporters (OATs) play a critical role in the handling of endogenous and exogenous organic anions by excretory and barrier tissues. Little is known about the OAT three-dimensional structure or substrate/protein interactions involved in transport. In this investigation, a theoretical three-dimensional model was generated for human OAT1 (hOAT1) based on fold recognition to the crystal structure of the glycerol 3-phosphate transporter (GlpT) from Escherichia coli. GlpT and hOAT1 share several sequence motifs as major facilitator superfamily members. The structural hOAT1 model shows that helices 5, 7, 8, 10, and 11 surround an electronegative putative active site ( approximately 830A(3)). The site opens to the cytoplasm and is surrounded by three residues not previously examined for function (Tyr(230) (domain 5) and Lys(431) and Phe(438) (domain 10)). Effects of these residues on p-aminohippurate (PAH) and cidofovir transport were assessed by point mutations in a Xenopus oocyte expression system. Membrane protein expression was severely limited for the Y230A mutant. For the K431A and F438A mutants, [(3)H]PAH uptake was less than 30% of wild-type hOAT1 uptake after protein expression correction. Reduced V(max) values for the F438A mutant confirmed lower protein expression. In addition, the F438A mutant exhibited an increased affinity for cidofovir but was not significantly different for PAH. Differences in handling of PAH and cidofovir were also observed for the Y230F mutant. Little uptake was determined for cidofovir, whereas PAH uptake was similar to wild-type hOAT1. Therefore, the hOAT1 structural model has identified two new residues, Tyr(230) and Phe(438), which are important for substrate/protein interactions.     

Identification and Enhancement of HLA-A2.1-Restricted CTL Epitopes in a New Human Cancer Antigen-POTE

Identification of CD8⁺ T cell epitopes that can induce T cells to kill tumor cells is a fundamental step for development of a peptide cancer vaccine. POTE protein is a newly identified cancer antigen that was found to be expressed in a wide variety of human cancers, including prostate, colon, lung, breast, ovary and pancreas. Here, we determined HLA-A2.1-restricted cytotoxic T lymphocyte (CTL) epitopes in the POTE protein, and also designed enhanced epitopes by amino acid (AA) substitutions. Five 9-mer peptides were first selected and their binding affinity to HLA-A2 molecules was measured by the T2 binding assay. POTE 272–280 and POTE 323–331 showed the strongest HLA-A2 binding affinity. AA substituted peptides POTE 252-9V (with valine at position 9), POTE 553-1Y (with tyrosine at position 1) and POTE 323-3F (with phenylalanine at position 3) conferred higher affinity for HLA-A2, and induced CTL responses cross-reactive with wild type antigens. While POTE 252-9V was the strongest in this respect, POTE 323-3F had the greatest increase in immunogenicity compared to wild type. Importantly, two modified epitopes (POTE-553-1Y and POTE-323-3F) induced CTLs that killed NCI-H522, a POTE-expressing HLA-A2⁺ human non-small cell lung cancer cell line, indicating natural endogenous processing of these epitopes. In conclusion, the immunogenicity of POTE epitopes can be enhanced by peptide modification to induce T cells that kill human cancer cells. A combination of POTE 553-1Y and POTE 323-3F epitopes might be an attractive vaccine strategy for HLA-A2 cancer patients to overcome tolerance induced by tumors and prevent escape.     

Investigating the conformational coupling between the transmembrane and cytoplasmic domains of a single-spanning membrane protein. A 1H-NMR study

PMP1 is a 38-residue single-spanning membrane protein whose C-terminal cytoplasmic domain, Y25-F38, is highly positively charged. The conformational coupling between the transmembrane span and the cytoplasmic domain of PMP1 was investigated from 1H-nuclear magnetic resonance data of two synthetic fragments: F9-F38, i.e. 80% of the whole sequence, and Y25-F38, the isolated cytoplasmic domain. Highly disordered in aqueous solution, the Y25-F38 peptide adopts a well-defined conformation in the presence of dodecylphosphocholine micelles. Compared with the long PMP1 fragment, this structure exhibits both native and non-native elements. Our results make it possible to assess the influence of a hydrophobic anchor on the intrinsic conformational propensity of a cytoplasmic domain.     

Identification and Clinical Implications of Novel MYO15A Mutations in a Non-consanguineous Korean Family by Targeted Exome Sequencing

Mutations of MYO15A are generally known to cause severe to profound hearing loss throughout all frequencies. Here, we found two novel MYO15A mutations, c.3871C>T (p.L1291F) and c.5835T>G (p.Y1945X) in an affected individual carrying congenital profound sensorineural hearing loss (SNHL) through targeted resequencing of 134 known deafness genes. The variant, p.L1291F and p.Y1945X, resided in the myosin motor and IQ2 domains, respectively. The p.L1291F variant was predicted to affect the structure of the actin-binding site from three-dimensional protein modeling, thereby interfering with the correct interaction between actin and myosin. From the literature analysis, mutations in the N-terminal domain were more frequently associated with residual hearing at low frequencies than mutations in the other regions of this gene. Therefore we suggest a hypothetical genotype-phenotype correlation whereby MYO15A mutations that affect domains other than the N-terminal domain, lead to profound SNHL throughout all frequencies and mutations that affect the N-terminal domain, result in residual hearing at low frequencies. This genotype-phenotype correlation suggests that preservation of residual hearing during auditory rehabilitation like cochlear implantation should be intended for those who carry mutations in the N-terminal domain and that individuals with mutations elsewhere in MYO15A require early cochlear implantation to timely initiate speech development.     

Monoclonal antibodies targeting the HR2 domain and the region immediately upstream of the HR2 of the S protein neutralize in vitro infection of severe acute respiratory syndrome coronavirus

We have previously shown that an Escherichia coli-expressed, denatured spike (S) protein fragment of the severe acute respiratory coronavirus, containing residues 1029 to 1192 which include the heptad repeat 2 (HR2) domain, was able to induce neutralizing polyclonal antibodies (C. T. Keng, A. Zhang, S. Shen, K. M. Lip, B. C. Fielding, T. H. Tan, C. F. Chou, C. B. Loh, S. Wang, J. Fu, X. Yang, S. G. Lim, W. Hong, and Y. J. Tan, J. Virol. 79:3289-3296, 2005). In this study, monoclonal antibodies (MAbs) were raised against this fragment to identify the linear neutralizing epitopes in the functional domain and to investigate the mechanisms involved in neutralization. Eighteen hybridomas secreting the S protein-specific MAbs were obtained. Binding sites of these MAbs were mapped to four linear epitopes. Two of them were located within the HR2 region and two immediately upstream of the HR2 domain. MAbs targeting these epitopes showed in vitro neutralizing activities and were able to inhibit cell-cell membrane fusion. These results provide evidence of novel neutralizing epitopes that are located in the HR2 domain and the spacer region immediately upstream of the HR2 of the S protein.     

Crystal structure of the Marasmius oreades mushroom lectin in complex with a xenotransplantation epitope

MOA, a lectin from the mushroom Marasmius oreades, is one of the few reagents that specifically agglutinate blood group B erythrocytes. Further, it is the only lectin known to have exclusive specificity for Galalpha(1,3)Gal-containing sugar epitopes, which are antigens that pose a severe barrier to animal-to-human organ transplantation. We describe here the structure of MOA at 2.4 A resolution, in complex with the linear trisaccharide Galalpha(1,3)Galbeta(1,4)GlcNAc. The structure is dimeric, with two distinct domains per protomer: the N-terminal lectin module adopts a ricinB/beta-trefoil fold and contains three putative carbohydrate-binding sites, while the C-terminal domain serves as a dimerization interface. This latter domain, which has an unknown function, reveals a novel fold with intriguing conservation of an active site cleft. A number of indications suggest that MOA may have an enzymatic function in addition to the sugar-binding properties.     

The solution structure of a chimeric LEKTI domain reveals a chameleon sequence

The conversion of an alpha-helical to a beta-strand conformation and the presence of chameleon sequences are fascinating from the perspective that such structural features are implicated in the induction of amyloid-related fatal diseases. In this study, we have determined the solution structure of a chimeric domain (Dom1PI) from the multidomain Kazal-type serine proteinase inhibitor LEKTI using multidimensional NMR spectroscopy. This chimeric protein was constructed to investigate the reasons for differences in the folds of the homologous LEKTI domains 1 and 6 [Lauber, T., et al. (2003) J. Mol. Biol. 328, 205-219]. In Dom1PI, two adjacent phenylalanine residues (F28 and F29) of domain 1 were substituted with proline and isoleucine, respectively, as found in the corresponding P4' and P5' positions of domain 6. The three-dimensional structure of Dom1PI is significantly different from the structure of domain 1 and closely resembles the structure of domain 6, despite the sequence being identical to that of domain 1 except for the two substituted phenylalanine residues and being only 31% identical to the sequence of domain 6. The mutation converted a short 3(10)-helix into an extended loop conformation and parts of the long COOH-terminal alpha-helix of domain 1 into a beta-hairpin structure. The latter conformational change occurs in a sequence stretch distinct from the region containing the substituted residues. Therefore, this switch from an alpha-helical structure to a beta-hairpin structure indicates a chameleon sequence of seven residues. We conclude that the secondary structure of Dom1PI is determined not only by the local protein sequence but also by nonlocal interactions.     

Structure of domain III of the blood-stage malaria vaccine candidate, Plasmodium falciparum apical membrane antigen 1 (AMA1)

Apical membrane antigen 1 of the malarial parasite Plasmodium falciparum (Pf AMA1) is a merozoite antigen that is considered a strong candidate for inclusion in a malaria vaccine. Antibodies reacting with disulphide bond-dependent epitopes in AMA1 block invasion of host erythrocytes by P.falciparum merozoites, and we show here that epitopes involving sites of mutations in domain III are targets of inhibitory human antibodies. The solution structure of AMA1 domain III, a 14kDa protein, has been determined using NMR spectroscopy on uniformly 15N and 13C/15N-labelled samples. The structure has a well-defined disulphide-stabilised core region separated by a disordered loop, and both the N and C-terminal regions of the molecule are unstructured. Within the disulphide-stabilised core, residues 443-447 form a turn of helix and residues 495-498 and 503-506 an anti-parallel beta-sheet with a distorted type I beta-turn centred on residues 500-501, producing a beta-hairpin-type structure. The structured region of the molecule includes all three disulphide bonds. The previously unassigned connectivities for two of these bonds could not be established with certainty from the NMR data and structure calculations, but were determined to be C490-C507 and C492-C509 from an antigenic analysis of mutated forms of this domain expressed using phage display. Naturally occurring mutations in domain III that are located far apart in the primary sequence tend to cluster in the region of the disulphide core in the three-dimensional structure of the molecule. The structure shows that nearly all the polymorphic sites have a high level of solvent accessibility, consistent with their location in epitopes recognised by protective antibodies. Even though domain III in solution contains significant regions of disorder in the structure, the disulphide-stabilised core that is structured is clearly an important element of the antigenic surface of AMA1 recognised by protective antibodies.     

YspD: A Potential Therapeutic Target for Drug Design to Combat Yersinia enterocolitica Infection

YspD is an annotated hydrophilic translocator of Ysa–Ysp type III secretion system of Yersinia enterocolitica. YspD has sequence, secondary structure and three-dimensional structure similar to other hydrophilic translocators. All hydrophilic translocators lack transmembrane region and possess intramolecular coiled-coil region. Disordered regions are mostly clustered at the N-terminal. Large loops provide flexibility, allowing conformational changes during oligomerization and protein–protein interaction. LcrV and PcrV have globular N-terminal and C-terminal domains, connected by intramolecular coiled-coil region. YspD, IpaD, SipD and BipD lack globular N-terminal and C-terminal domains. Their N-terminal and C-terminal domain have a bundle like structure connected by the intramolecular coiled-coil. The intramolecular coiled-coil regions (helix-5&9) of YspD showed maximum conservation, followed by helices at N-terminal. Polar interactions are mainly involved during dimerization of YspD, involving polar residues from helix-9 of both the YspD molecules. A methionine forms the boundary of interaction between the two YspD molecules. The two YspD molecules are arranged in antiparallel fashion to form the dimer. N-terminal of YspB interacted with C-terminal of YspD molecule to form a pentameric complex, consisting four YspD molecules and one YspB molecule. Sequence, structural similarity and presence of specific motifs in YspD (like chaperone protein) indicate the ability of N-terminal domain to show self-chaperoning activity and regulate folding and conformational state of YspD during its journey from the bacterial cytoplasm to the needle tip. Structural analysis of YspD and its mechanism of interaction with other proteins would enable us to design drugs against this hydrophilic protein to combat Yersinia infection.

     

A new siglec family member, siglec-10, is expressed in cells of the immune system and has signaling properties similar to CD33.

The siglecs (sialic acid-binding Ig-like lectins) are a distinct subset of the Ig superfamily with adhesion-molecule-like structure. We describe here a novel member of the siglec protein family that shares a similar structure including five Ig-like domains, a transmembrane domain, and a cytoplasmic tail containing two ITIM-signaling motifs. Siglec-10 was identified through database mining of an asthmatic eosinophil EST library. Using the Stanford G3 radiation hybrid panel we were able to localize the genomic sequence of siglec-10 within the cluster of genes on chromosome 19q13.3-4 that encode other siglec family members. We have demonstrated that siglec-10 is an immune system-restricted membrane-bound protein that is highly expressed in peripheral blood leukocytes as demonstrated by Northern, RT-PCR and flow cytometry. Binding assays determined that the extracellular domain of siglec-10 was capable of binding to peripheral blood leukocytes. The cytoplasmic tail of siglec-10 contains four tyrosines, two of which are embedded in ITIM-signaling motifs (Y597 and Y667) and are likely involved in intracellular signaling. The ability of tyrosine kinases to phosphorylate the cytoplasmic tyrosines was evaluated by kinase assay using wild-type siglec-10 cytoplasmic domain and Y-->F mutants. The majority of the phosphorylation could be attributed to Y597 andY667. Further experiments with cell extracts suggest that SHP-1 interacts with Y667 and SHP-2 interacts with Y667 in addition to another tyrosine. This is very similar to CD33, which also binds the phosphatases SHP-1 and SHP-2, therefore siglec-10, as CD33, may be characterized as an inhibitory receptor.     

Analysis of murine B-cell epitopes on Eastern equine encephalitis virus glycoprotein E2

The Eastern equine encephalitis virus (EEEV) E2 protein is one of the main targets of the protective immune response against EEEV. Although some efforts have done to elaborate the structure and immune molecular basis of Alphaviruses E2 protein, the published data of EEEV E2 are limited. Preparation of EEEV E2 protein-specific antibodies and define MAbs-binding epitopes on E2 protein will be conductive to the antibody-based prophylactic and therapeutic and to the study on structure and function of EEEV E2 protein. In this study, 51 EEEV E2 protein-reactive monoclonal antibodies (MAbs) and antisera (polyclonal antibodies, PAbs) were prepared and characterized. By pepscan with MAbs and PAbs using enzyme-linked immunosorbent assay, we defined 18 murine linear B-cell epitopes. Seven peptide epitopes were recognized by both MAbs and PAbs, nine epitopes were only recognized by PAbs, and two epitopes were only recognized by MAbs. Among the epitopes recognized by MAbs, seven epitopes were found only in EEEV and two epitopes were found both in EEEV and Venezuelan equine encephalitis virus (VEEV). Four of the EEEV antigenic complex-specific epitopes were commonly held by EEEV subtypes I/II/III/IV (1-16aa, 248-259aa, 271-286aa, 321-336aa probably located in E2 domain A, domain B, domain C, domain C, respectively). The remaining three epitopes were EEEV type-specific epitopes: a subtype I-specific epitope at amino acids 108–119 (domain A), a subtype I/IV-specific epitope at amino acids 211–226 (domain B) and a subtype I/II/III-specific epitope at amino acids 231–246 (domain B). The two common epitopes of EEEV and VEEV were located at amino acids 131–146 and 241–256 (domain B). The generation of EEEV E2-specific MAbs with defined specificities and binding epitopes will inform the development of differential diagnostic approaches and structure study for EEEV and associated alphaviruses.     

Crystal structure of a phage library-derived single-chain Fv fragment complexed with turkey egg-white lysozyme at 2.0 A resolution

The three-dimensional structure of the single-chain Fv fragment 1F9 in complex with turkey egg-white lysozyme (TEL) has been determined to a nominal resolution of 2.0 A by X-ray diffraction. The scFv fragment 1F9 was derived from phage-display libraries in two steps and binds both hen and turkey egg-white lysozyme, although the level of binding affinity is two orders of magnitude greater for the turkey lysozyme. The comparison of the crystal structure with a model of the single-chain Fv fragment 1F9 in complex with hen egg-white lysozyme (HEL) reveals that in the latter a clash between Asp101 in lysozyme and Trp98 of the complementarity determining region H3 of the heavy chain variable domain occurs. This is the only explanation apparent from the crystal structure for the better binding of TEL compared to HEL.The binding site topology on the paratope is not simply a planar surface as is usually found in antibody-protein interfaces, but includes a cleft between the light chain variable domain and heavy chain variable domain large enough to accommodate a loop from the lysozyme. The scFv fragment 1F9 recognizes an epitope on TEL that differs from the three antigenic determinants recognized in other known crystal structures of monoclonal antibodies in complex with lysozyme.     

Bioenergetic and structural consequences of allotopic expression of subunit 8 of yeast mitochondrial ATP synthase. The hydrophobic character of residues 23 and 24 is essential for maximal activity and structural stability of the enzyme complex.

Subunit 8 (Y8), a mitochondrially encoded subunit of the F0 sector of the F1F0-ATP synthase is essential for oxidative phosphorylation. We have previously introduced the technique of allotopic expression to study the structure/function of Y8, whereby an artificial Y8 gene is expressed in the nucleus of cells lacking a functional mitochondrial Y8, thus generating assembly of a functional F1F0-ATPase complex. In this paper we show that when a gene encoding an essentially unmodified version of Y8 is allotopically expressed, ATP synthesis and hydrolysis rates, as well as efficiency of oxidative phosphorylation, were similar to those of the parental wild-type strain in which Y8 is naturally expressed in mitochondria. We then tested the requirement for the hydrophobicity of the central domain (residues 14-32), which possibly represents a transmembrane stem, by introducing adjacent negative charges at different positions of Y8. One of the variants thus generated, which carries the double substitution Leu23-->Asp, Leu24-->Asp, when expressed in a strain lacking endogenous Y8, gave rise to cells which grew very slowly by oxidative phosphorylation. Measurement of bioenergetic parameters showed two major defects in these cells relative to control cells allotopically expressing unmodified Y8. First, the activity of the F1F0-ATP synthase was significantly decreased. ATP synthesis and state 3 of respiration were reduced by approximately 30-40%. ATP hydrolysis was reduced by approximately 30% and was almost insensitive to the F0 inhibitor oligomycin. Second, the physical coupling between the two sectors of the enzyme, as well as the stability of the F1 sector itself, were affected as shown by decreased recovery of F0 sector [8, 9, b, oligomycin sensitivity-conferring protein (OSCP), d, h and f] and F1 sector (alpha, gamma, delta) subunits in immunoprecipitates of ATP synthase. This study indicates that Y8 not only performs an important role in the structure of the mitochondrial complex but also in its activity. We conclude that the hydrophobic character of amino acids 23 and 24 in the middle of the putative transmembrane stem of Y8 is essential for coupling proton transport through F0 to ATP synthesis on F1.     

The structure of the sarcomeric M band: localization of defined domains of myomesin, M-protein, and the 250-kD carboxy-terminal region of titin by immunoelectron microscopy

The M band of vertebrate cross-striated myofibrils has remained an enigmatic structure. In addition to myosin thick filaments, two major structural proteins, myomesin and M-protein, have been localized to the M band. Also, titin is expected to be anchored in this structure. To begin to understand the molecular layout of these three proteins, a panel of 16 polyclonal and monoclonal antibodies directed against unique epitopes of defined sequence was assembled, and immunoelectron microscopy was used to locate the position of the epitopes at the sarcomere level. The results allow the localization and orientation of defined domains of titin, myomesin, and M-protein at high resolution. The 250-kD carboxy-terminal region of titin clearly enters the M band with the kinase domain situated approximately 52 nm from the central M1- line. The positions of three additional epitopes are compatible with the view that the titin molecule reaches approximately 60 nm into the opposite sarcomere half. Myomesin also seems to bridge the central M1- line and is oriented parallel to the long axis of the myofibril. The neighboring molecules are oriented in an antiparallel and staggered fashion. The amino-terminal portion of the protein, known to contain a myosin binding site, seems to adopt a specific three-dimensional arrangement. While myomesin is present in both slow and fast fibers, M- protein is restricted to fast fibers. It appears to be organized in a fundamentally different manner: the central portion of the polypeptide is around the M1-line, while the terminal epitopes seem to be arranged along thick filaments. This orientation fits the conspicuously stronger M1-lines in fast twitch fibers. Obvious implications of this model are discussed.     

Chimeric animal and plant viruses expressing epitopes of outer membrane protein F as a combined vaccine against Pseudomonas aeruginosa lung infection

Outer membrane protein F of Pseudomonas aeruginosa has vaccine efficacy against infection by P. aeruginosa as demonstrated in a variety of animal models. Through the use of synthetic peptides, three surface-exposed epitopes have been identified. These are called peptides 9 (aa 261-274 in the mature F protein, TDAYNQKLSERRAN), 10 (aa 305-318, NATAEGRAINRRVE), and 18 (aa 282-295, NEYGVEGGRVNAVG). Both the peptide 9 and 10 epitopes are protective when administered as a vaccine. In order to develop a vaccine that is suitable for use in humans, including infants with cystic fibrosis, the use of viral vector systems to present the protective epitopes has been investigated. An 11-amino acid portion of epitope 10 (AEGRAINRRVE) was successfully inserted into the antigenic B site of the hemagglutinin on the surface of influenza virus. This chimeric influenza virus protects against challenge with P. aeruginosa in the mouse model of chronic pulmonary infection. Attempts to derive a chimeric influenza virus carrying epitope 9 have been unsuccessful. A chimeric plant virus, cowpea mosaic virus (CPMV), with epitopes 18 and 10 expressed in tandem on the large coat protein subunit (CPMV-PAE5) was found to elicit antibodies that reacted exclusively with the 10 epitope and not with epitope 18. Use of this chimeric virus as a vaccine afforded protection against challenge with P. aeruginosa in the mouse model of chronic pulmonary infection. Chimeric CPMVs with a single peptide containing epitopes 9 and 18 expressed on either of the coat proteins are in the process of being evaluated. Epitope 9 was successfully expressed on the coat protein of tobacco mosaic virus (TMV), and this chimeric virus is protective when used as a vaccine in the mouse model of chronic pulmonary infection. However, initial attempts to express epitope 10 on the coat protein of TMV have been unsuccessful. Efforts are continuing to construct chimeric viruses that express both the 9 and 10 epitopes in the same virus vector system. Ideally, the use of a vaccine containing two epitopes of protein F is desirable in order to greatly reduce the likelihood of selecting a variant of P. aeruginosa that escapes protective antibodies in immunized humans via a mutation in a single epitope within protein F. When the chimeric influenza virus containing epitope 10 and the chimeric TMV containing epitope 9 were given together as a combined vaccine, the immunized mice produced antibodies directed toward both epitopes 9 and 10. The combined vaccine afforded protection against challenge with P. aeruginosa in the chronic pulmonary infection model at approximately the same level of efficacy as provided by the individual chimeric virus vaccines. These results prove in principle that a combined chimeric viral vaccine presenting both epitopes 9 and 10 of protein F has vaccine potential warranting continued development into a vaccine for use in humans.     

NMR solution structure of Ole e 6, a major allergen from olive tree pollen

Ole e 6 is a pollen protein from the olive tree (Olea europaea) that exhibits allergenic activity with a high prevalence among olive-allergic individuals. The three-dimensional structure of Ole e 6 has been determined in solution by NMR methods. This is the first experimentally determined structure of an olive tree pollen allergen. The structure of this 50-residue protein is based on 486 upper limit distance constraints derived from nuclear Overhauser effects and 24 torsion angle restraints. The global fold of Ole e 6 consists of two nearly antiparallel alpha-helices, spanning residues 3-19 and 23-33, that are connected by a short loop and followed by a long, unstructured C-terminal tail. Viewed edge-on, the structured N terminus has a dumbbell-like shape with the two helices on the outside and with the hydrophobic core, mainly composed of 3 aromatic and 6 cysteine residues, on the inside. All the aromatic rings lie on top of and pack against the three disulfide bonds. The lack of thermal unfolding, even at 85 degrees C, indicates a high conformational stability. Based on the analysis of the molecular surface, we propose five plausible epitopes for IgE recognition. The results presented here provide the structural foundation for future experiments to verify the antigenicity of the proposed epitopes, as well as to design novel hypoallergenic forms of the protein suitable for diagnosis and treatment of type-I allergies. In addition, three-dimensional structure features of Ole e 6 are discussed to provide a basis for future functional studies.     

Spectroscopy and a high-resolution crystal structure of Tyr263 mutants of cyanobacterial phytochrome Cph1

Phytochromes are biliprotein photoreceptors that can be photoswitched between red-light-absorbing state (Pr) and far-red-light-absorbing state (Pfr). Although three-dimensional structures of both states have been reported, the photoconversion and intramolecular signaling mechanisms are still unclear. Here, we report UV-Vis absorbance, fluorescence and CD spectroscopy along with various photochemical parameters of the wild type and Y263F, Y263H and Y263S mutants of the Cph1 photosensory module, as well as a 2.0-Å-resolution crystal structure of the Y263F mutant in its Pr ground state. Although Y263 is conserved, we show that the aromatic character but not the hydroxyl group of Y263 is important for Pfr formation. The crystal structure of the Y263F mutant (Protein Data Bank ID: 3ZQ5) reaffirms the ZZZssa chromophore configuration and provides a detailed picture of its binding pocket, particularly conformational heterogeneity around the chromophore. Comparison with other phytochrome structures reveals differences in the relative position of the PHY (phytochrome specific) domain and the interaction of the tongue with the extreme N-terminus. Our data support the notion that native phytochromes in their Pr state are structurally heterogeneous.