The 17Å structure of the 420kDa lobster clottable protein by single particle reconstruction from cryoelectron micrographs

Biochemical, histological and transcriptional response of intestines in Litopenaeus vannamei under chronic zinc exposure

Zinc (Zn) is an essential trace element for the normal physiological function of aquatic organisms, but it could become toxic to organisms when the concentration increased in water. As the first line of defense, the shrimp intestines are the most susceptible organ to environmental stress. In this study, the chronic toxicity of 0 (control, IC), 0.01(IL), 0.1(IM) and 1 mg/L (IH) Zn in intestines of Litopenaeus vannamei was investigated from the perspectives of biochemical, histological and transcriptional changes after exposure for 30 days. The results showed that the intestinal tissue basement membrane is swollen in the IM and IH groups and detached in the IH group. The total antioxidant capacities (T-AOC) were reduced while the content of malondialdehyde (MDA) were increased significantly in IM and IH groups. The production of reactive oxygen species (ROS) was increased significantly in IH group. Many differentially expressed genes (DEGs) were identified in IL, IM and IH groups, respectively. GO and KEGG enrichment analyses were conducted on the DEGs to obtain the underlying biological processes and pathways. The gene modules related to the sample were identified by weighted gene co-expression network analysis (WGCNA), and genes in modules highly corelated with IH group were mainly enriched in immune related pathways. Nine DEGs were selected for validation by quantitative real time PCR (qRT-PCR) and the expression profiles of these DEGs kept a well consistent with the high-throughput data, which confirmed reliability of transcriptome results. Additionally, 10 DEGs were screened to detect the changes of expression level in different groups. All these results indicated that Zn exposure could damage the intestinal barrier, provoke oxidative stress, reduce the immune function, increase the susceptibility to bacterial infections of L. vannamei and cause inflammation, ultimately result in cell apoptosis. Our study provides more perspective on the stress response of crustacean under Zn exposure.

Hemolymph proteins: An overview across marine arthropods and molluscs

In this compilation we collect information about the main protein components in hemolymph and stress the continued interest in their study. The reasons for such an attention span several areas of biological, veterinarian and medical applications: from the notions for better dealing with the species - belonging to phylum Arthropoda, subphylum Crustacea, and to phylum Mollusca - of economic interest, to the development of 'marine drugs' from the peptides that, in invertebrates, act as antimicrobial, antifungal, antiprotozoal, and/or antiviral agents. Overall, the topic most often on focus is that of innate immunity operated by classes of pattern-recognition proteins. SIGNIFICANCE: The immune response in invertebrates relies on innate rather than on adaptive/acquired effectors. At a difference from the soluble and membrane-bound immunoglobulins and receptors in vertebrates, the antimicrobial, antifungal, antiprotozoal and/or antiviral agents in invertebrates interact with non-self material by targeting some common (rather than some highly specific) structural motifs. Developing this paradigm into (semi) synthetic pharmaceuticals, possibly optimized through the modeling opportunities offered by computational biochemistry, is one of the lessons today's science may learn from the study of marine invertebrates, and specifically of the proteins and peptides in their hemolymph.

Crustacean Hemolymph Lipoproteins

Lipoproteins mediate the transport of apolar lipids in the hydrophilic environment of physiological fluids such as the vertebrate blood and the arthropod hemolymph. In this overview, we will focus on the hemolymph lipoproteins in Crustacea that have received most attention during the last years: the high density lipoprotein/β-glucan binding proteins (HDL-BGBPs), the vitellogenins (VGs), the clotting proteins (CPs) and the more recently discovered large discoidal lipoproteins (dLPs). VGs are female specific lipoproteins which supply both proteins and lipids as storage material for the oocyte for later use by the developing embryo. Unusual within the invertebrates, the crustacean yolk proteins-formerly designated VGs-are more related to the ApoB type lipoproteins of vertebrates and are now termed apolipocrustaceins. The CPs on the other hand, which are present in both sexes, are related to the (sex specific) VGs of insects and vertebrates. CPs serve in hemostasis and wound closure but also as storage proteins in the oocyte. The HDL-BGBPs are the main lipid transporters, but are also involved in immune defense. Most crustacean lipoproteins belong to the family of the large lipid transfer proteins (LLTPs) such as the intracellular microsomal triglyceride transfer protein, the VGs, CPs and the dLPs. In contrast, the HDL-BGBPs do not belong to the LLTPs and their relationship with other lipoproteins is unknown. However, they originate from a common precursor with the dLPs, whose functions are as yet unknown. The majority of lipoprotein studies have focused on decapod crustaceans, especially shrimps, due to their economic importance. However, we will present evidence that the HDL-BGBPs are restricted to the decapod crustaceans which raises the question as to the main lipid transporting proteins of the other crustacean groups. The diversity of crustaceans lipoproteins thus appears to be more complex than reflected by the present state of knowledge.

The clotting system in decapod crustaceans: History, current knowledge and what we need to know beyond the models

Hemolymph coagulation is among the major arms of the humoral immune response in crustaceans. According to the current model, hemolymph clotting in decapod crustacean relies mostly on the polymerization of the plasmatic clotting protein (CP) which is directly promoted by calcium-depended transglutaminase (TGase) released from hemocytes upon microbial stimulus or injury. However, the type of hemocytes containing TGase, and hence how the TGase is released, might vary among species. Thus, we discourse here about possible mechanisms for clotting initiation. On the other hand, the initiation of coagulation reaction in the absence of microbial elicitors is poorly understood and seems to involve hemocytes lability, yet the mechanism remains unknown. A cellular clottable protein called coagulogen, different to the plasma CP, occurs in several species and could be related with the immune response, but the biological relevance of this protein is unknown. It is also demonstrated that the clotting response is actively involved in defense against pathogens. In addition, both TGase and the CP show pleiotropic functions, and although both proteins are relatively conserved, some of their physic-chemical properties vary significantly. The occurrence of differences in the clotting system in crustaceans is conceivable given the high number of species and their diverse ecology. Results from still non-studied decapods may provide explanation for some of the issues presented here from an evolutionary perspective.

Structural characterization of proteins and complexes using small-angle X-ray solution scattering

Small-angle scattering of X-rays (SAXS) is an established method for the low-resolution structural characterization of biological macromolecules in solution. The technique provides three-dimensional low-resolution structures, using ab initio and rigid body modeling, and allow one to assess the oligomeric state of proteins and protein complexes. In addition, SAXS is a powerful tool for structure validation and the quantitative analysis of flexible systems, and is highly complementary to the high resolution methods of X-ray crystallography and NMR. At present, SAXS analysis methods have reached an advanced state, allowing for automated and rapid characterization of protein solutions in terms of low-resolution models, quaternary structure and oligomeric composition. In this communication, main approaches to the characterization of proteins and protein complexes using SAXS are reviewed. The tools for the analysis of proteins in solution are presented, and the impact that these tools have made in modern structural biology is discussed.

The Pandinus imperator haemolymph lipoprotein, an unusual phosphatidylserine carrying lipoprotein

The haemolymph lipoprotein of the scorpion, Pandinus imperator was isolated and characterised. Contrary to the lipoproteins of insects and the discoidal HDL-lipoproteins of a crayfish and polychaete, the Pandinus lipoprotein consists of three instead of two apoproteins (apoPiLp I = 230 kDa, apoPiLp II = 130 kDa and apoPiLp III = 120 kDa). The apolipoproteins are arranged in varying stoichiometries as judged by cross-linking experiments. In lipoprotein samples from individual animals, the two smaller subunits occurred in a 1:1 stoichiometry, while the relative amount of the 230 kDa peptide varied. The lipoprotein is a slightly heart-shaped HDL with a diameter of approximately 15 nm. It is present in two densities of 1100 and 1190 kg/m(3), of which the latter is by far more abundant. The native molecular mass was estimated to be approximately 500 kDa. The lipid content was determined as 33.5% and consists of approximately 70% neutral lipids and approximately 30% phospholipids. Strikingly, 42.5% of the phospholipids is phosphatidylserine while phosphatidylcholine and phosphatidylethanolamine account for 55.1% and approximately 2.3%, respectively. Carbohydrate analysis suggests the presence of only high-mannose-type N-glycans. N-glycan profiling shows glycans corresponding to a size of 8.0-11.5 hexose units.

The evolution of plasma cholesterol: direct utility or a "spandrel" of hepatic lipid metabolism?

Fats provide a concentrated source of energy for multicellular organisms. The efficient transport of fats through aqueous biological environments raises issues concerning effective delivery to target tissues. Furthermore, the utilization of fatty acids presents a high risk of cytotoxicity. Improving the efficiency of fat transport while simultaneously minimizing the cytotoxic risk confers distinct selective advantages. In humans, most of the plasma cholesterol is associated with low-density lipoprotein (LDL), a metabolic by-product of very-low-density lipoprotein (VLDL), which originates in the liver. However, the functions of VLDL are not clear. This paper reviews the evidence that LDL arose as a by-product during the natural selection of VLDL. The latter, in turn, evolved as a means of improving the efficiency of diet-derived fatty acid storage and utilization, as well as neutralizing the potential cytotoxicity of fatty acids while conserving their advantages as a concentrated energy source. The evolutionary biology of lipid transport processes has provided a fascinating insight into how and why these VLDL functions emerged during animal evolution. As causes of historical origin must be separated from current utilities, our spandrel-LDL theory proposes that LDL is a spandrel of VLDL selection, which appeared non-adaptively and may later have become crucial for vertebrate fitness.

Expression of clottable protein of tiger shrimp (Penaeus monodon) in gonads and its possible role as nutrient source for the embryo

We have investigated the expression of clottable protein (CP) in gonad of tiger shrimp (Penaeus monodon) and extent of its phosphorylation. Polyclonal antibodies against purified CP were prepared from rabbit serum. Using this anti-CP antiserum, the temporal expression of CP in gonads of tiger shrimp was analyzed. It was found that the CP occurs only in mature ovaries but not in immature ovaries and testes. Results of RT-PCR confirmed that these tissues expressed low levels of CP mRNA transcripts. Upon eyestalk-ablation, the ovaries in female shrimps were induced to develop, and the CP expression levels in ovaries were traced chronically by RT-PCR analyses. The expression level peaked on day 3 with an increase of about 40 folds relative to the basal level and returned to normal level (as the control shrimp) at day 12. The shrimp embryos at different intervals from spawning to 16h post-spawning were also collected, and it was found that CP contents were gradually decreased in the embryos until the nauplii were hatched. In addition, purified CP was shown to react with specific anti-phosphoserine, anti-phosphothreonine, and anti-phosphotyrosine antibodies suggesting that CP is a phosphoprotein with all types of phosphorylations. Taken together the results suggest that expression of CP in shrimp ovaries is coupled to ovarian development and CP possibly supply nutrition for shrimp embryo.

X-ray solution scattering (SAXS) combined with crystallography and computation: defining accurate macromolecular structures, conformations and assemblies in solution

Crystallography supplies unparalleled detail on structural information critical for mechanistic analyses; however, it is restricted to describing low energy conformations of macromolecules within crystal lattices. Small angle X-ray scattering (SAXS) offers complementary information about macromolecular folding, unfolding, aggregation, extended conformations, flexibly linked domains, shape, conformation, and assembly state in solution, albeit at the lower resolution range of about 50 A to 10 A resolution, but without the size limitations inherent in NMR and electron microscopy studies. Together these techniques can allow multi-scale modeling to create complete and accurate images of macromolecules for modeling allosteric mechanisms, supramolecular complexes, and dynamic molecular machines acting in diverse processes ranging from eukaryotic DNA replication, recombination and repair to microbial membrane secretion and assembly systems. This review addresses both theoretical and practical concepts, concerns and considerations for using these techniques in conjunction with computational methods to productively combine solution scattering data with high-resolution structures. Detailed aspects of SAXS experimental results are considered with a focus on data interpretation tools suitable to model protein and nucleic acid macromolecular structures, including membrane protein, RNA, DNA, and protein-nucleic acid complexes. The methods discussed provide the basis to examine molecular interactions in solution and to study macromolecular flexibility and conformational changes that have become increasingly relevant for accurate understanding, simulation, and prediction of mechanisms in structural cell biology and nanotechnology.

Cloning and characterization of hemolymph clottable proteins of kuruma prawn (Marsupenaeus japonicus) and white shrimp (Litopenaeus vannamei)

The hemolymph clottable protein (CP) of Marsupenaeus japonica (designated as Mj-CP) was purified by a DEAE anion-exchanger and a Sepharose CL-6B gel filtration column. In the presence of Ca(2+), it formed stable clots in vitro upon the addition of the hemocytes lysate containing transglutaminase. Results of gel filtration chromatography and SDS-PAGE indicated that Mj-CP mainly existed as disulfide-linked homodimers of 390 kDa. Specific primers were designed; PCR as well as RACE help to clone and sequence Mj-CP cDNA of 5660 bp. The predicted CP-precursor contains a signal peptide followed by a subunit of 1671 amino acids (isoelectric point 5.6), including two RGD motifs and three potential N-glycosylation sites. Mj-CP is structurally 80% and 38% identical to the CPs of tiger shrimp and crayfish, respectively. Likewise, CP cDNA of white shrimp (Litopenaeus vannamei) was also cloned and sequenced; the predicted CP has 1666 amino acid residues and an isoelectric point of 5.2. Both CPs bear potential transglutaminase cross-linking sites, i.e. seven Ser-Lys-Thr repeats near the N-terminus, a Ser- and Gln-rich region in the middle, and polyGln (n=8-11) near the C-terminus. Phylogenetic analyses of crustacean CPs and vitellogenins revealed divergent evolution of the two protein families. By RT-PCR, the sub-cuticular epidermis was identified as one of the major tissues that express CP in M. japonica.

Tissue-specific expression and regulation of the haemolymph clottable protein of tiger shrimp (Penaeus monodon)

The clottable protein (CP) involved in Penaeus monodon haemolymph coagulation has previously been characterized and cloned. Polyclonal antibodies against purified CP were also prepared from rabbit serum. By Western blot analyses, we showed occurrence of CP in the shrimp central nervous system, gill, and lymphoid organ. Results of RT-PCR further indicated that the central nervous system, gill, and lymphoid organ transcribed more CP, heart and hepatopancreas transcribed less, while the haemocytes and the muscle did not. We further analyzed the CP distribution within shrimp lymphoid organ by immunohistochemical method, CP was found to localise in stromal cells of lymphoid organ rather than in the developing haemocytes. In addition, concentrations and regulation of the plasma CP under normal and artificially traumatic conditions were studied with rocket immunoelectrophoresis. The average plasma CP concentration in normal intermolt shrimps was elevated from 3 mg ml(-1) to above 12 mg ml(-1) after successive blood-withdrawing for a week. The production and secretion of CP apparently were increased more than 4 folds to compensate its loss. Our result also suggested that the shrimp sinus gland endocrine system is not directly required for the expression and up-regulation of CP.