Cloning, expression and biochemical characterization of a basic-acidic hybrid phospholipase A2-II from Agkistrodon halys pallas

A general approach to protein folding using thermostable exoshells

In vitro protein folding is a complex process which often results in protein aggregation, low yields and low specific activity. Here we report the use of nanoscale exoshells (tES) to provide complementary nanoenvironments for the folding and release of 12 highly diverse protein substrates ranging from small protein toxins to human albumin, a dimeric protein (alkaline phosphatase), a trimeric ion channel (Omp2a) and the tetrameric tumor suppressor, p53. These proteins represent a unique diversity in size, volume, disulfide linkages, isoelectric point and multi versus monomeric nature of their functional units. Protein encapsulation within tES increased crude soluble yield (3-fold to >100-fold), functional yield (2-fold to >100-fold) and specific activity (3-fold to >100-fold) for all the proteins tested. The average soluble yield was 6.5 mg/100 mg of tES with charge complementation between the tES internal cavity and the protein substrate being the primary determinant of functional folding. Our results confirm the importance of nanoscale electrostatic effects and provide a solution for folding proteins in vitro.

Complementary DNA sequencing and identification of mRNAs from the venomous gland of Agkistrodon piscivorus leucostoma

To advance our knowledge on the snake venom composition and transcripts expressed in venom gland at the molecular level, we constructed a cDNA library from the venom gland of Agkistrodon piscivorus leucostoma for the generation of expressed sequence tags (ESTs) database. From the randomly sequenced 2112 independent clones, we have obtained ESTs for 1309 (62%) cDNAs, which showed significant deduced amino acid sequence similarity (scores >80) to previously characterized proteins in National Center for Biotechnology Information (NCBI) database. Ribosomal proteins make up 47 clones (2%) and the remaining 756 (36%) cDNAs represent either unknown identity or show BLASTX sequence identity scores of <80 with known GenBank accessions. The most highly expressed gene encoding phospholipase A(2) (PLA(2)) accounting for 35% of A. p. leucostoma venom gland cDNAs was identified and further confirmed by crude venom applied to sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) electrophoresis and protein sequencing. A total of 180 representative genes were obtained from the sequence assemblies and deposited to EST database. Clones showing sequence identity to disintegrins, thrombin-like enzymes, hemorrhagic toxins, fibrinogen clotting inhibitors and plasminogen activators were also identified in our EST database. These data can be used to develop a research program that will help us identify genes encoding proteins that are of medical importance or proteins involved in the mechanisms of the toxin venom.

Mapping structural determinants of biological activities in snake venom phospholipases A2 by sequence analysis and site directed mutagenesis

In addition to their catalytic activity, snake venom phospholipases A2 (vPLA2) present remarkable diversity in their biological effects. Sequence alignment analyses of functionally related PLA2 are frequently used to predict the structural determinants of these effects, and the predictions are subsequently evaluated by site directed mutagenesis experiments and functional assays. In order to improve the predictive potential of computer-based analysis, a simple method for scanning amino acid variation analysis (SAVANA) has been developed and included in the analysis of the lysine 49 PLA2 myotoxins (Lys49-PLA2). The SAVANA analysis identified positions in the C-terminal loop region of the protein, which were not identified using previously available sequence analysis tools. Site directed mutagenesis experiments of bothropstoxin-I, a Lys49-PLA2 isolated from the venom of Bothrops jararacussu, reveals that these residues are exactly those involved in the determination of myotoxic and membrane damaging activities. The SAVANA method has been used to analyse presynaptic neurotoxic and anti-coagulant vPLA2s, and the predicted structural determinants of these activities are in excellent agreement with the available results of site directed mutagenesis experiments. The positions of residues involved in the myotoxic and neurotoxic determinants demonstrate significant overlap, suggesting that the multiple biological effects observed in many snake vPLA2s are a consequence of superposed structural determinants on the protein surface.

Secretory phospholipase A(2) induces apoptosis via a mechanism involving ceramide generation

Secretory phospholipase A(2) (sPLA(2)) plays important roles in cellular signaling and various biological events. In this study, we examined the biological effects and the potential signaling mechanism of purified sPLA(2) in MV1Lu cells. Three types of snake venom sPLA(2) were purified and their enzymatic activities were characterized by using various lipid substrates prepared from [3H]-myristate-labeled cells and by determining their effects on the induction of arachidonic acid (AA) release. The purified sPLA(2) induced apoptosis in Mv1Lu cells in a dose- and time-dependent manner, and was associated with a rapid increase in the intracellular ceramide level. Similar apoptotic effects were observed in Mv1Lu cells treated with exogenous ceramide analog, C(2)- and C(8)-ceramide. Moreover, treatment of cells with sphingomyelinase (SMase), which reduced the intracellular SM level, enhanced the apoptotic response to sPLA(2)s. sPLA(2)s also displayed an inhibitory effect on bradykinin-induced phospholipase D (PLD) activity, which can be imitated by exogenous ceramide. Our data indicate that sPLA(2) induces cell apoptosis via a mechanism involving increased ceramide generation.

Expression of an active recombinant lysine 49 phospholipase A(2) myotoxin as a fusion protein in bacteria

ACL myotoxin (ACLMT) is a K49 phospholipase A(2)-like protein isolated from the venom of the snake Agkistrodon contortrix laticinctus (broad-banded copperhead) that induces necrosis of skeletal muscle. We have previously cloned and sequenced the cDNA coding for ACLMT from a venom gland cDNA library. In order to perform structure and function studies, we have developed an expression system for production of ACLMT as a fusion protein with maltose binding protein (MBP) from the periplasm of bacteria, using the pMAL-p2 expression vector. The cDNA coding for the mature toxin without the signal peptide was amplified by PCR and subcloned into the pMAL-p2 vector. The new plasmid (pMAL-MT) was used to transform BL21(DE3) E. coli cells. Culture of transformed cells induced with IPTG led to the expression of a 60 kDa fusion protein which strongly reacts with anti-native ACLMT antibodies. The fusion protein was purified from the bacterial periplasm by affinity chromatography in an amylose column and by gel filtration. The purified fusion protein (MBP-rACLMT) was able to induce necrosis of skeletal muscle of mice very similar to that caused by the native myotoxin.

Phospholipases A2 from Callosellasma rhodostoma venom gland cloning and sequencing of 10 of the cDNAs, three-dimensional modelling and chemical modification of the major isozyme

Callosellasma rhodostoma (Malayan pitviper) is a monotypic Asian pitviper of medical importance. Three acidic phospholipases A2 (PLA2s) and one basic PLA2-homolog were purified from its venom while 10 cDNAs encoding distinct PLA2s were cloned from venom glands of a Thailand specimen of this species. Complete amino-acid sequences of the purified PLA2s were successfully deduced from their cDNA sequences. Among the six un-translated PLA2 cDNAs, two apparently result from recombination of its Lys49-PLA2 gene with its Asp49-PLA2 genes. The acidic PLA2s inhibit platelet-aggregation, while the noncatalytic PLA2-homolog induces local edema. This basic PLA2-homolog contains both Asp49 and other, unusual substitutions unique for the venom Lys49-PLA2 subtype (e.g. Leu5, Trp6, Asn28 and Arg34). Three-dimensional modelling of the basic protein revealed a heparin-binding region, and an abnormal calcium-binding pocket, which may explain its low catalytic activity. Oxidation of up to six of its Met residues or coinjection with heparin reduced its edema-inducing activity but methylation of its active site His48 did not. The distinct Arg/Lys-rich and Met-rich region at positions 10-36 of the PLA2 homolog presumably are involved in its heparin-binding and the cell membrane-interference leading to edema and myotoxicity.

Structure of basic phospholipase A2 from Agkistrodon halys Pallas: implications for its association, hemolytic and anticoagulant activities

The basic phospholipase A2 (PLA2) from the venom of Agkistrodon halys Pallas is a potent hemolytic toxin and anticoagulant. Crystal structure of the enzyme complexed with detergent n-octyl beta-D-glucopyranoside (beta-OG) in monoclinic crystal form has been determined to 2.6 A resolution. Beta-OG molecules were found in the hydrophobic channels of the enzyme. SDS-PAGE and dynamic light scattering measurements showed that the enzyme had a strong tendency to dimerise in aqueous solution. In the crystal structure the enzyme molecules associate into a tetramer with pseudo 222 symmetry, and the interfacial recognition site linked dimers constituting the tetramer have intensive interface interactions, and may be stable in solution. The structure reveals a unique positively charged face at the C-terminal region and a characteristic non-cationic 'anticoagulant' region (53-77). The face is supposed to be the hemolytic site, and based on sequence and structure comparison residues Trp70 and Glu53 instead of the basic residues in 'anticoagulant' region might play an important role in the anticoagulant activity.