Aplysia attractin: biophysical characterization and modeling of a water-borne pheromone

Transcriptional responses of attractin gene in the mosquito Anopheles culicifacies: A synergistic neuro-olfactory regulation

Background & objectives

Attractin, is a large multi-domain protein which has regulatory functions in multiple physiological processes and thus have strong therapeutic potential. In invertebrates, it was first identified as a water-borne protein pheromone that plays important role in chemical communication and coordinates reproductive activities. But its role in mosquitoes/insects remains unknown. Our unexpected discovery of attractin homolog from the olfactory tissue of Anopheles culicifacies mosquito prompted us to investigate the possible role of Ac-attractin (Ac-atrn) in diverse behavioural responses, e.g. feeding, mating and other non-genetic stresses.

Methods

A homology search analysis was performed to identify the full length attractin (Ac-atrn) gene of Anopheles culicifacies mosquito. To unravel its molecular function during external and internal stresses, extensive real-time PCR was performed in the neuro-olfactory tissues of the adult mosquitoes as well as in the larval stages. Further, a behavioural assay was conducted to elucidate its role in mosquitoes mating behaviour.

Results

The results indicated that Ac-atrn is a 3942 bp long transcript which encodes a 1313 amino acid protein, having multiple domains including CUB, EGF, Keltch, etc, with 80-90% homology to other insect/mosquito homologs. Ac-atrn gene was dominantly expressed in the young larvae and its expression was elevated in response to the fresh food supply in the starved larvae. Cold stress temporarily arrested the expression of Ac-atrn gene. In case of adult mosquitoes, olfactory and brain tissue showed relatively higher expression of Ac-atrn than reproductive organs. Although, starvation did not yield significant changes in olfactory tissues, but aging and nutritional stress modulated Ac-atrn expression in the brain tissue. Furthermore, a circadian rhythm dependent change in the expression of Ac-atrn of virgin and mated mosquitoes (both sexes), indicates that Ac-atrn might also have a pheromone guided role during swarm formation and mating behaviour.

Interpretation & conclusion

The relative expression profiling of Ac-atrn gene in the larvae during nutritional and cold stress suggested its possible role in mediating chemical communication towards the food source and in thermal regulation of young larvae. Similarly, it might have crucial regulatory role in the stress management and survival of adult mosquitoes. The results revealed that Ac-atrn gene is a global regulator of many physiological processes in mosquitoes including stress response and mating behaviour and thus might be a potential target to design novel intervention strategy against mosquitoes.

A complex set of sex pheromones identified in the cuttlefish Sepia officinalis

Background

The cephalopod mollusk Sepia officinalis can be considered as a relevant model for studying reproduction strategies associated to seasonal migrations. Using transcriptomic and peptidomic approaches, we aim to identify peptide sex pheromones that are thought to induce the aggregation of mature cuttlefish in their egg-laying areas.

Results

To facilitate the identification of sex pheromones, 576 5′-expressed sequence tags (ESTs) were sequenced from a single cDNA library generated from accessory sex glands of female cuttlefish. Our analysis yielded 223 unique sequences composed of 186 singletons and 37 contigs. Three major redundant ESTs called SPα, SPα′ and SPβ were identified as good candidates for putative sex pheromone transcripts and are part of the 87 unique sequences classified as unknown. The alignment of translated SPα and SPα′ revealed a high level of conservation, with 98.4% identity. Translation led to a 248-amino acid precursor containing six peptides with multiple putative disulfide bonds. The alignment of SPα-α′ with SPβ revealed a partial structural conservation, with 37.3% identity. Translation of SPβ led to a 252-amino acid precursor containing five peptides. The occurrence of a signal peptide on SPα, SPα′ and SPβ showed that the peptides were secreted. RT-PCR and mass spectrometry analyses revealed a co-localization of transcripts and expression products in the oviduct gland. Preliminary in vitro experiments performed on gills and penises revealed target organs involved in mating and ventilation.

Conclusions

The analysis of the accessory sex gland transcriptome of Sepia officinalis led to the identification of peptidic sex pheromones. Although preliminary functional tests suggested the involvement of the α3 and β2 peptides in ventilation and mating stimulation, further functional investigations will make it possible to identify the complete set of biological activities expected from waterborne pheromones.

PCP consensus sequences of flaviviruses: correlating variance with vector competence and disease phenotype

BACKGROUND

Computational methods are needed to design multivalent vaccines against flaviviruses (FVs) such as the West Nile virus or the dengue virus (DENV).

OBJECTIVE

We aimed to use physicochemical property (PCP) consensus sequences of FV strains to delineate conserved motifs, areas of maximum variability, and specific loci that correlate with arthropod vector, serotype, and disease severity.

METHODS

PCP consensus sequences for 27 species were prepared from 928 annotated sequences catalogued in Flavitrack. Alignments of these correlated well with the known structures of the NS3 protease domain and envelope (E) proteins. The PCPMer suite was used to identify motifs common to all FVs. Areas of PCP variability that correlated with phenotype were plotted on the structures.

RESULTS

Despite considerable diversity at the amino acid level, PCPs for both proteins were well conserved throughout the FVs. A series of insertions in E separated tick- from mosquito-borne viruses and all arthropod-borne viruses from isolates with no known vector or directly from insects. Comparison of a PCP consensus sequence of E derived from 600 DENV strains (DENV600) with individual ones for DENV1-DENV4 showed that most major serotype-specific variation occurs near these insertions. The DENV600 differed from one prepared from eight hemorrhagic or fatal strains from four DENV serotypes at only three positions, two of which overlap known escape mutant sites.

CONCLUSIONS

Comparing consensus sequences showed that substantial changes occur in only a few areas of the E protein. PCP consensus sequences can contribute to the design of multivalent vaccines.

Comprehensive 3D-modeling of allergenic proteins and amino acid composition of potential conformational IgE epitopes

Similarities in sequences and 3D structures of allergenic proteins provide vital clues to identify clinically relevant immunoglobulin E (IgE) cross-reactivities. However, experimental 3D structures are available in the Protein Data Bank for only 5% (45/829) of all allergens catalogued in the Structural Database of Allergenic Proteins (SDAP, http://fermi.utmb.edu/SDAP). Here, an automated procedure was used to prepare 3D-models of all allergens where there was no experimentally determined 3D structure or high identity (95%) to another protein of known 3D structure. After a final selection by quality criteria, 433 reliable 3D models were retained and are available from our SDAP Website. The new 3D models extensively enhance our knowledge of allergen structures. As an example of their use, experimentally derived "continuous IgE epitopes" were mapped on 3 experimentally determined structures and 13 of our 3D-models of allergenic proteins. Large portions of these continuous sequences are not entirely on the surface and therefore cannot interact with IgE or other proteins. Only the surface exposed residues are constituents of "conformational IgE epitopes" which are not in all cases continuous in sequence. The surface exposed parts of the experimental determined continuous IgE epitopes showed a distinct statistical distribution as compared to their presence in typical protein-protein interfaces. The amino acids Ala, Ser, Asn, Gly and particularly Lys have a high propensity to occur in IgE binding sites. The 3D-models will facilitate further analysis of the common properties of IgE binding sites of allergenic proteins.

Molecular MALDI imaging: an emerging technology for neuroscience studies

Mass spectrometry (MS) has become an essential tool for the detection, identification, and characterization of the molecular components of biological processes, such as those responsible for the dynamic properties of the nervous system. Generally, the application of these powerful techniques requires the destruction of the specimen under study, but recent technological advances have made it possible to apply the matrix-assisted laser desorption/ionization (MALDI) MS technique directly to tissue sections. The major advantage of direct MALDI analysis is that it enables the acquisition of local molecular expression profiles, while maintaining the topographic integrity of the tissue and avoiding time-consuming extraction, purification, and separation steps, which have the potential for introducing artifacts. With automation and the ability to display complex spectral data using imaging software, it is now possible to create multiple 2D maps of selected biomolecules in register with tissue sections, a method now known as MALDI Imaging, or MSI (for Mass Spectrometry Imaging). This creates, for example, an opportunity to correlate functional states, determined a priori with live recording or imaging, with the corresponding molecular maps obtained at the time the tissue is frozen and analyzed with MSI. We review the increasing application of MALDI Imaging to the analysis of molecular distributions of proteins and peptides in nervous tissues of both vertebrates and invertebrates, focusing in particular on recent studies of neurodegenerative diseases and early efforts to implement assays of neuronal development.

Aplysia temptin - the 'glue' in the water-borne attractin pheromone complex

Temptin, a component of the complex of water-borne protein pheromones that stimulate attraction and mating behavior in the marine mollusk Aplysia, has sequence homology to the epidermal growth factor (EGF)-like domains of higher organisms that mediate protein-cell surface contact during fertilization and blood coagulation. In this work, recombinant temptin for structural and functional studies was produced in Escherichia coli using a cold shock promoter and purified by RP-HPLC. CD spectra confirmed a predominantly beta-sheet structure. Two disulfide bonds were determined via limited proteolysis and MS. One internal disulfide (Cys57-Cys77) was predicted from initial alignments with class I EGF-like domains; the second, between Cys18 and Cys103, could protect temptin against proteolysis in seawater and stabilize its interacting surface. A three-dimensional model of temptin was prepared with our MPACK suite, based on the Ca(2+)-binding, EGF-like domain of the extracellular matrix protein fibrillin. Two temptin residues, Trp52 and Trp79, which align with cysteine residues conserved in fibrillins, lie adjacent to and could stabilize the disulfide bonds and a proposed metal-binding loop. The water-borne pheromone attractin in egg cordon eluates is complexed with other proteins. Docking results with our model and the NMR structure of attractin suggest that one face of temptin interacts with the pheromone, perhaps controlling its access to the cellular receptors. Gel shifts confirmed that temptin complexes with wild-type attractin. These results indicate that temptin, analogous to the role of fibrillin in controlling transforming growth factor-beta concentration, modulates pheromone signaling by direct binding to attractin.

Cold-adaptation in Sea-water-borne Signal Proteins: Sequence and NMR Structure of the Pheromone En-6 from the Antarctic Ciliate Euplotes nobilii

Ciliates of Euplotes species constitutively secrete pleiotropic protein pheromones, which are capable to function as prototypic autocrine growth factors as well as paracrine inducers of mating processes. This paper reports the amino acid sequence and the NMR structure of the pheromone En-6 isolated from the antarctic species Euplotes nobilii. The 63-residue En-6 polypeptide chain forms three alpha-helices in positions 18-25, 36-40 and 46-56, which are arranged in an up-down-up three-helix bundle forming the edges of a distorted trigonal pyramid. The base of the pyramid is covered by the N-terminal heptadecapeptide segment, which includes a 3(10)-turn of residues 3-6. This topology is covalently anchored by four long-range disulfide bonds. Comparison with the smaller pheromones of E. raikovi, a closely related species living in temperate waters, shows that the two-pheromone families have the same three-helix bundle architecture. It then appears that cold-adaptation of the En proteins is primarily related to increased lengths of the chain-terminal peptide segments and the surface-exposed loops connecting the regular secondary structures, and to the presence of solvent-exposed clusters of negatively charged side-chains.

Recombinant production and structural studies of the Aplysia water-borne protein pheromone enticin indicates it has a novel disulfide stabilized fold

Enticin is one of three Aplysia proteins released during egg laying that act in concert with the pheromone attractin to attract other Aplysia and stimulate mating behavior. Whereas the enticin cDNA predicts a 69-residue mature protein, enticin isolated from the albumen gland was found to be posttranslationally processed in vivo by cleavage at Arg(50) residue to generate a smaller 49-residue mature peptide. The Arg(50) cleavage site is conserved in enticin from both Aplysia californica and Aplysia brasiliana. In order to generate sufficient enticin for structural studies, recombinant full-length protein was produced in a soluble form in Escherichia coli using a cold shock promoter-based protein expression system. The enticin cDNA was cloned into the bacterial vector pCold III, and efficiently expressed, as determined by amino acid microsequence and immunoblot analyses. Recombinant enticin, which contained an additional N-terminal 13-residue translation-enhancing element, was purified by reversed-phase HPLC and compared to enticin isolated from the albumen gland. The three disulfide bonds in enticin were characterized by endoproteinase Glu-C proteolysis followed by mass spectrometric characterization of the fragments. The cysteine pairing, for both recombinant and native enticin, was I-II, III-IV, and V-VI, confirming that the protein produced in the bacterial system was correctly folded. The circular dichroism spectrum of the recombinant protein indicated it was predominantly alpha-helical. While this was consistent with fold recognition server results indicating a fold for enticin similar to that of attractin, the disulfide bonding pattern differs. A model for enticin was prepared based on its helical structure and these disulfide constraints.

NMR structure of the viral peptide linked to the genome (VPg) of poliovirus

VPgs are essential for replication of picornaviruses, which cause diseases such as poliomyelitis, foot and mouth disease, and the common cold. VPg in infected cells is covalently linked to the 5' end of the viral RNA, or, in a uridylylated form, free in the cytoplasm. We show here the first solution structure for a picornaviral VPg, that of the 22-residue peptide from poliovirus serotype 1. VPg in buffer is inherently flexible, but a single conformer was obtained by adding trimethylamine N-oxide (TMAO). TMAO had only minor effects on the TOCSY spectrum. However, it increased the amount of structured peptide, as indicated by more peaks in the NOESY spectrum and an up to 300% increase in the ratio of normalized NOE cross peak intensities to that in buffer. The data for VPg in TMAO yielded a well defined structure bundle with 0.6 A RMSD (versus 6.6 A in buffer alone), with 10-30 unambiguous constraints per residue. The structure consists of a large loop region from residues 1 to 14, from which the reactive tyrosinate projects outward, and a C-terminal helix from residues 18 to 21 that aligns the sidechains of conserved residues on one face. The structure has a stable docking position at an area on the poliovirus polymerase crystal structure identified as a VPg binding site by mutagenesis studies. Further, UTP and ATP dock in a base-specific manner to the reactive face of VPg, held in place by residues conserved in all picornavirus VPgs.

Determining functionally important amino acid residues of the E1 protein of Venezuelan equine encephalitis virus

A new method for predicting interacting residues in protein complexes, InterProSurf, was applied to the E1 envelope protein of Venezuelan equine encephalitis (VEEV). Monomeric and trimeric models of VEEV-E1 were constructed with our MPACK program, using the crystal structure of the E1 protein of Semliki forest virus as a template. An alignment of the E1 sequences from representative alphavirus sequences was used to determine physical chemical property motifs (likely functional areas) with our PCPMer program. Information on residue variability, propensity to be in protein interfaces, and surface exposure on the model was combined to predict surface clusters likely to interact with other viral or cellular proteins. Mutagenesis of these clusters indicated that the predictions accurately detected areas crucial for virus infection. In addition to the fusion peptide area in domain 2, at least two other surface areas play an important role in virus infection. We propose that these may be sites of interaction between the E1-E1 and E1-E2 subdomains of the envelope proteins that are required to assemble the functional unit. The InterProSurf method is, thus, an important new tool for predicting viral protein interactions. These results can aid in the design of new vaccines against alphaviruses and other viruses.

Newly identified water-borne protein pheromones interact with attractin to stimulate mate attraction in Aplysia

The water-borne protein attractin is a potent sex pheromone involved in forming and maintaining mating and egg-laying aggregations in the marine mollusk Aplysia. Binary blends of attractin and either enticin, temptin, or seductin, three other Aplysia protein pheromones, stimulate mate attraction. The four pheromones are thought to act in concert during egg-laying. The new data presented here show that: (1) the water-borne odor of non-laying Aplysia brasiliana further increases the attractiveness of attractin and of eggs in T-maze bioassays. This suggests that individual Aplysia release additional factors that enhance the effects of attractin, enticin, temptin, and seductin during egg-laying; (2) the N-terminal region of enticin aligns well with the conserved epidermal growth factor (EGF)-like domain of mammalian reproductive proteins known as fertilins, which may mediate intercellular adhesion interactions between eggs and sperm; (3) temptin, according to fold recognition servers, may also have an EGF-like fold. Enticin and temptin also have conserved metal binding sequences that may play a role in their signaling behavior. These results suggest that aspects of mammalian egg-sperm interactions (fertilins) may have evolved from pheromonal signaling mechanisms. We also review the structure, expression, localization, release, and behavioral actions of attractin, enticin, temptin, and seductin.

Structural basis for epitope sharing between group 1 allergens of cedar pollen

The group 1 allergens are a major cause of cedar pollen hypersensitivity in several geographic areas. Allergens from several taxa have been shown to cross-react. The goal of these studies was to compare the structural features of the shared and unique epitopes of the group 1 allergen from mountain cedar (Jun a 1) and Japanese cedar (Cry j 1). An array of overlapping peptides from the sequence of Jun a 1 and a panel of monoclonal anti-Cry j 1 antibodies were used to identify the IgE epitopes recognized by cedar-sensitive patients from Texas and Japan. IgE from Japanese patients reacted with peptides representing one of the two linear epitopes within the highly conserved beta-helical core structure and both epitopes within less ordered loops and turns near the N- and C-termini of Jun a 1. A three-dimensional (3D) model of the Cry j 1, based on the crystal structure of Jun a 1, indicated a similar surface exposure for the four described epitopes of Jun a 1 and the homologous regions of Cry j 1. The monoclonal antibodies identified another shared epitope, which is most likely conformational and a unique Cry j 1 epitope that may be the previously recognized glycopeptide IgE epitope. Defining the structural basis for shared and unique epitopes will help to identify critical features of IgE epitopes that can be used to develop mimotopes or identify allergen homologues for vaccine development.

Aplysia seductin is a water-borne protein pheromone that acts in concert with attractin to stimulate mate attraction

Mate attraction in Aplysia involves the long-distance water-borne protein pheromones attractin, enticin, and temptin which are released during egg-laying. Other water-borne pheromones are predicted to act in concert with attractin, enticin, and temptin, but their identities were unknown. We recently identified a highly expressed Aplysia californica albumen gland gene (Alb-23) that encoded a novel protein by differential library screening of an albumen gland cDNA library. To determine whether Alb-23 ('seductin') was a water-borne pheromone, we employed Western blot analysis, purification and expression of albumen gland proteins, immunolocalization studies, pheromone secretion assays, comparative genomics, and behavioral bioassays. Immunoreactive seductin was detected in eluates of egg cordons, indicating that seductin was secreted onto the cordon during egg laying. Aplysia brasiliana seductin was 94% identical to its A.californica homolog. In T-maze attraction assays, the combination of attractin and seductin was significantly attractive to potential mates, whereas either protein alone was not. Data from this and previous studies support the hypothesis that seductin is a water-borne protein pheromone that acts in concert with attractin, enticin, and temptin to attract Aplysia to form and maintain mating aggregations.

Molluscan attractins, a family of water-borne protein pheromones with interspecific attractiveness

The marine mollusk Aplysia releases the water-borne pheromone attractin during egg laying. This small protein stimulates the formation and maintenance of mating and egg-laying aggregations. Attractin has been characterized from five Aplysia species: A. californica, A. brasiliana, A. fasciata, A. vaccaria, and A. depilans. We describe here the isolation of attractin from Bursatella leachii, and show that it belongs to the same protein family. The pattern of residue conservation, especially the six invariant cysteines, suggests that all of these attractins have a common fold. The nuclear magnetic resonance solution structure of A. californica attractin contains two antiparallel alpha-helices, the second of which contains the heptapeptide sequence IEECKTS that has been implicated in attractin function. Synthetic peptides containing this IEECKTS region are attractive, and mutating surface exposed charged residues within this region of attractin abolishes attractin activity. This suggests that the second helix is an essential part of the receptor-binding interface. In contrast to the peptide pheromonal attractants in amphibians, which are species specific, the attractins are, to our knowledge, the first water-borne peptide or protein pheromone family in invertebrates and vertebrates that are not species specific.

The presence of APGWamide in Octopus vulgaris: a possible role in the reproductive behavior

The concerted action of many neuropeptides has been implicated in the nervous control of specific behaviors in many molluscs. In the present study, the presence of amidated tetrapeptide Ala-Pro-Gly-Trp-NH2 (APGWamide) in those lobes that are involved in the control of reproductive behavior in Octopus vulgaris has been investigated. APGWamide immunoreactivity was mainly confined to the posterior olfactory lobule and in the inferior frontal system. These areas are involved in Octopus in the processing of either chemotactile sense or olfaction. From these lobes, immunoreactive fibers reached other lobes of the central nervous system (CNS) which could be indirectly involved in the reproductive behavior. APGWamide immunoreactivity was also present in the glandular cells of the oviducal gland in the female reproductive system. These results constitute the first detailed immunolocalization of APGWamide in cephalopods and open a new insight into the possible effects that both distant and close chemical stimuli can exert on neuropeptidergic circuitries, which may affect the reproductive behavior of cephalopods.

Peptide and protein pheromones in molluscs

Pheromones have been implicated in the control of a number of behaviors in molluscs, but few peptide pheromones have been characterized in these animals. Peptide pheromones include: (1) a family of water-borne peptide pheromonal attractants (attractins) in the gastropod Aplysia that are released during egg laying and attract other Aplysia to form egg-laying and mating aggregations; (2) a tetrapeptide (ILME) in the cephalopod Sepia that elutes from egg masses and is thought to be involved in the transport of oocytes in the genital tract during egg laying; and (3) a Sepia sperm-attracting peptide (SepSAP; PIDPGVamide) that is released from oocytes during egg laying to facilitate external fertilization.

Structural and functional analysis of Aplysia attractins, a family of water-borne protein pheromones with interspecific attractiveness

Mate attraction in Aplysia involves a long-distance water-borne signal (the protein pheromone attractin), which is released during egg laying. Aplysia californica attractin attracts species that produce closely related attractins, such as Aplysia brasiliana, whose geographic distribution does not overlap that of A. californica. This finding suggests that other mollusks release attractin-related pheromones to form and maintain breeding aggregations. We describe four additional members of the attractin family: A. brasiliana, Aplysia fasciata, Aplysia depilans (which aggregates with A. fasciata aggregations), and Aplysia vaccaria (which aggregates with A. californica aggregations). On the basis of their sequence similarity with A. californica attractin, the attractin proteins fall into two groups: A. californica, A. brasiliana, and A. fasciata (91-95% identity), and A. depilans and A. vaccaria (41-43% identity). The sequence similarity within the attractin family, the conserved six cysteines, and the compact fold of the NMR solution structure of A. californica attractin suggest a common fold for this pheromone family containing two antiparallel helices. The second helix contains the IEECKTS sequence conserved in Aplysia attractins. Mutating surface-exposed charged residues within this heptapeptide sequence abolishes attractin activity, suggesting that the second helix is an essential part of the receptor-binding interface.

Characterization of Aplysia enticin and temptin, two novel water-borne protein pheromones that act in concert with attractin to stimulate mate attraction

Mate attraction in Aplysia involves a long-distance water-borne signal (attractin) that is released during egg laying. Other pheromones are predicted to be released during egg laying that act in concert with albumen gland attractin to stimulate attraction, but their identities are unknown. To identify other candidate water-borne pheromones, we employed differential library screening of an albumen gland cDNA library, Northern blot analysis, purification, characterization, cloning, and expression of albumen gland proteins, matrix-assisted laser desorption ionization mass spectrometry, pheromone secretion assays, behavioral bioassays, immunolocalization studies, and comparative genomics. Four genes, Alb-23, Alb-24, Alb-69, and Alb-172, were highly expressed in Aplysia californica albumen glands and encoded novel proteins. The products of the Alb-24 ("enticin") and Alb-172 ("temptin") precursors were soluble and highly abundant in albumen gland extracts, whereas Alb-23 and Alb-69 were membrane-associated proteins. A comparative analysis showed that the predicted Aplysia brasiliana enticin and temptin proteins were 90 and 91% identical, respectively, to their A. californica homologs. T-maze attraction bioassay studies have previously demonstrated that egg cordons alone are attractive to Aplysia but that attractin alone is not. In the present study, however, the combination of attractin, enticin, and temptin was found to be significantly attractive to potential mates and doubled the number of animals attracted to this stimulus compared with control animals. The combined data strongly suggest that enticin and temptin are novel candidate water-borne protein pheromones that act in concert with attractin to attract Aplysia to form and maintain egglaying and mating aggregations.

A conserved heptapeptide sequence in the waterborne attractin pheromone stimulates mate attraction in Aplysia

Mate attraction in the marine mollusk Aplysia involves long-distance waterborne chemical signaling via the release of the peptide pheromone attractin during egg laying. Aplysia californica attractin attracts conspecifics, reduces the latency to mating, and stimulates hermaphroditic mating. Four additional members of the Aplysia attractin family have recently been characterized from Aplysia brasiliana, Aplysia fasciata, Aplysia depilans, and Aplysia vaccaria. The five sequences differ significantly, but share six cysteine residues and the strictly conserved sequence Ile30-Glu-Glu-Cys-Lys-Thr-Ser36. Attractin is attractive to geographically and evolutionarily distant species, suggesting that the conserved heptapeptide region may be important for mate attraction. Consistent with this prediction, a synthetic constrained cyclic peptide that contains the conserved heptapeptide sequence is significantly attractive in T-maze bioassays. The attractins are the first family of waterborne peptide pheromones characterized in invertebrates and are unique in that family members are not species-specific pheromonal attractants.

Selectively receptor-blind measles viruses: Identification of residues necessary for SLAM- or CD46-induced fusion and their localization on a new hemagglutinin structural model

Measles virus (MV) enters cells either through the signaling lymphocyte activation molecule SLAM (CD150) expressed only in immune cells or through the ubiquitously expressed regulator of complement activation, CD46. To identify residues on the attachment protein hemagglutinin (H) essential for fusion support through either receptor, we devised a strategy based on analysis of morbillivirus H-protein sequences, iterative cycles of mutant protein production followed by receptor-based functional assays, and a novel MV H three-dimensional model. This model uses the Newcastle disease virus hemagglutinin-neuraminidase protein structure as a template. We identified seven amino acids important for SLAM- and nine for CD46 (Vero cell receptor)-induced fusion. The MV H three-dimensional model suggests (i) that SLAM- and CD46-relevant residues are located in contiguous areas in propeller beta-sheets 5 and 4, respectively; (ii) that two clusters of SLAM-relevant residues exist and that they are accessible for receptor contact; and (iii) that several CD46-relevant amino acids may be shielded from direct receptor contacts. It appears likely that certain residues support receptor-specific H-protein conformational changes. To verify the importance of the H residues identified with the cell-cell fusion assays for virus entry into cells, we transferred the relevant mutations into genomic MV cDNAs. Indeed, we were able to recover recombinant viruses, and we showed that these replicate selectively in cells expressing SLAM or CD46. Selectively receptor-blind viruses will be used to study MV pathogenesis and may have applications for the production of novel vaccines and therapeutics.

NMR solution structure of attractin, a water-borne protein pheromone from the mollusk Aplysia californica

Water-borne protein pheromones are essential for coordination of reproductive activities in many marine organisms. In this paper, we describe the first structure of a pheromone protein from a marine organism, that of attractin (58 residues) from Aplysia californica. The NMR solution structure was determined from TOCSY, NOESY, and DQF-COSY measurements of recombinant attractin expressed in insect cells. The sequential resonance assignments were done with standard manual procedures. Approximately 90% of the 949 unambiguous NOESY cross-peaks were assigned automatically with simultaneous three-dimensional structure calculation using our NOAH/DIAMOD/FANTOM program suite. The final bundle of energy-refined structures is well-defined, with an average rmsd value to the mean structure of 0.72 +/- 0.12 A for backbone and 1.32 +/- 0.11 A for heavy atoms for amino acids 3-47. Attractin contains two antiparallel helices, made up of residues Ile9-Gln16 and I30-S36. The NMR distance constraints are consistent with the three disulfide bonds determined by mass spectroscopy (C4-C41, C13-C33, and C20-C26), where the first two could be directly determined from NOESY cross-peaks between CH beta protons of the corresponding cysteines. The second helix contains the (L/I)(29)IEECKTS(36) sequence conserved in attractins from five species of Aplysia that could interact with the receptor. The sequence and structure of this region are similar to those of the recognition helix of the Er-11 pheromone of the unicellular ciliate Euplotes raikovi, suggesting a possible common pathway for intercellular communication of these two distinct pheromone families.

Behavioral characterization of attractin, a water-borne peptide pheromone in the genus aplysia

Pheromones play a significant role in coordinating reproductive activity in many animals, including opisthobranch molluscs of the genus APLYSIA: Although solitary during most of the year, these simultaneous hermaphrodites gather into breeding aggregations during the reproductive season. The aggregations contain both mating and egg-laying animals and are associated with masses of egg cordons. The egg cordons are a source of pheromones that attract other Aplysia to the area, reduce their latency to mating, and induce egg laying. One of these water-borne egg cordon pheromones ("attractin") has been characterized and shown to be attractive in T-maze assays. Attractin is the first water-borne peptide pheromone characterized in invertebrates. In the current studies, behavioral assays were used to better characterize the attraction, and to examine whether attractin can induce mating. Although the two activities could be related (i.e., attraction occurring because animals were looking for a partner), this was not tested. T-maze assays showed that attractin works as part of a bouquet of odors: the peptide is attractive only when Aplysia brasiliana is part of the stimulus. The animal does not need to be a conspecific, perhaps explaining why multiple species may be associated with one aggregation. Native and recombinant attractin are equally attractive, verifying that N-glycosylation at residue 8 is not required for attraction. Mating studies showed that both native and recombinant attractin reduce the latency to mating. The effects are larger when hermaphroditic mating is considered: in addition to reducing latency, attractin doubles the number of pairs mating as hermaphrodites. The effect may result from attractin stimulating both animals to mate as males and would be consistent with behaviors previously seen in the T-maze. Attractin may thus be contributing to the formation of copulatory chains and rings seen in aggregations in the field. These results may be interpreted in two ways: (1). attractin has multiple activities that contribute to the establishment and maintenance of the aggregation; or (2). the induced desire to mate may make attractin attractive when it is presented in conjunction with an animal. In either case, the results open the door for cellular and molecular studies of mechanism of action.

Peptide products of the atrial gland are not water-borne reproductive pheromones during egg laying in Aplysia

Mate attraction in Aplysia involves long-distance water-borne signaling via the secretion of the peptide pheromone attractin from the exocrine albumen gland during egg laying. Previous studies have shown that a second exocrine organ, the atrial gland, produces abundant egg-laying hormone (ELH) precursor-related peptides and mollusk-derived growth factor (MDGF), and crude extracts of the atrial gland are attractive in T-maze attraction assays. However, it is not known whether these peptides and proteins are secreted during egg laying. In this report, seawater eluates of freshly laid egg cordons were concentrated and fractionated by C18 RP-HPLC, and the resulting major peaks were examined by amino acid compositional analysis, microsequence analysis, and electrospray mass spectrometry. Concentrated egg cordon eluates were also examined by immunoblot analysis using anti-MDGF antisera as probe. The combined data demonstrated that the atrial gland of Aplysia californica does not secrete detectable levels of either ELH precursor-related peptides or MDGF during egg laying. Although the atrial gland is the last major exocrine organ to make contact with eggs before they are laid, the gland does not appear to secrete water-borne peptide pheromones during egg laying.

Detecting potential IgE-reactive sites on food proteins using a sequence and structure database, SDAP-food

The high incidence of food allergies, including oral allergy syndrome, represent major considerations when introducing new crops and foods. A new structural database of allergenic proteins, SDAP-Food, http://fermi.utmb.edu/SDAP/, has been developed to aid in predicting the IgE-binding potential of novel food proteins and cross-reactivities among known allergens. The site is designed to facilitate the first steps of a decision tree approach to determine the allergenicity of a given protein, based on the sequence and structural similarity to known allergens and their IgE binding sites. Immunological tests can then be used to confirm the predictions. A hierarchical procedure for identifying potential allergens, using a physical property-based sequence similarity index, has been designed to identify regions that resemble known IgE binding sites. As an example, SDAP tools were used to find food allergen sequences similar to an IgE binding site of the Jun a 3 allergen from mountain cedar pollen. The SDAP sequence similarity search matched the Jun a 3 epitope to regions in several food allergens, including cherry (Pru av 2), apple (Mal d 2) and pepper (Cap a 1), which are, like Jun a 3, members of the plant pathogenesis-related (PR-5) protein family. Homology modeling, using our EXDIS/DIAMOD/FANTOM program suite, indicated a similar surface location and structure for the potential epitope region on all of these allergens. The quantitative approach presented here can be used as part of a screening process for potential allergenicity of recombinant food products.

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/.

Structure-function analysis of decay-accelerating factor: identification of residues important for binding of the Escherichia coli Dr adhesin and complement regulation

Decay-accelerating factor (DAF), a complement regulatory protein, also serves as a receptor for Dr adhesin-bearing Escherichia coli. The repeat three of DAF was shown to be important in Dr adhesin binding and complement regulation. However, Dr adhesins do not bind to red blood cells with the rare polymorphism of DAF, designated Dr(a(-)); these cells contain a point mutation (Ser165-Leu) in DAF repeat three. In addition, monoclonal antibody IH4 specific against repeat three was shown to block both Dr adhesin binding and complement regulatory functions of DAF. Therefore, to identify residues important in binding of Dr adhesin and IH4 and in regulating complement, we mutated 11 amino acids-predominantly those in close proximity to Ser165 to alanine-and expressed these mutations in Chinese hamster ovary cells. To map the mutations, we built a homology model of repeat three based on the poxvirus complement inhibitory protein, using the EXDIS, DIAMOD, and FANTOM programs. We show that perhaps Ser155, and not Ser165, is the key amino acid that interacts with the Dr adhesin and amino acids Gly159, Tyr160, and Leu162 and also aids in binding Dr adhesin. The IH4 binding epitope contains residues Phe148, Ser155, and L171. Residues Phe123 and Phe148 at the interface of repeat 2-3, and also Phe154 in the repeat three cavity, were important for complement regulation. Our results show that residues affecting the tested functions are located on the same loop (148 to 171), at the same surface of repeat three, and that the Dr adhesin-binding and complement regulatory epitopes of DAF appear to be distinct and are approximately 20 A apart.

Structural characterization of a protein pheromone from a cold-adapted (Antarctic) single-cell eukaryote, the ciliate Euplotes nobilii

Free-living species of ciliated Protozoa control their vegetative (mitotic) proliferation and mating (sexual) processes by diffusible, cell type-specific protein signals (pheromones). One of these molecules, designated En-2, was isolated from a species, Euplotes nobilii, living in the stably cold marine waters of Antarctica, and its complete amino acid sequence of 60 residues was determined by automated Edman degradation of the whole protein and peptides generated by trypsin digestion. The proposed sequence is: DIEDFYTSETCPYKNDSQLA(20)WDTCSGGTGNCGTVCCGQCF(40)SFPVSQSCAGMADSNDCPNA(60). The En-2 structure appears to be characterized by an adaptive insertion of a glycine-rich motif potentially capable to confer more flexibility to a functionally critical region of the molecule.