Intraspecific Differences in the Venom of Crotalus durissus cumanensis from Colombia

Biochemical and biological differences in the venom of Crotalus durissus cumanensis from three ecoregions of Colombia were evaluated. Rattlesnakes were collected from the geographic areas of Magdalena Medio (MM), Caribe (CA) and Orinoquía (OR). All three regionally distributed venoms contain proteases, PLA₂s and the basic subunit of crotoxin. However, only crotamine was detected in the CA venom. The highest lethality, coagulant, phospholipase A₂ and hyaluronidase activities were found in the MM venom. Also, some differences, observed by western blot and immunoaffinity, were found in all three venoms when using commercial antivenoms. Furthermore, all three eco-regional venoms showed intraspecific variability, considering the differences in the abundance and intensity of their components, in addition to the activity and response to commercial antivenoms.

Computer-controlled spot-scan imaging of crotoxin complex crystals with 400 keV electrons at near-atomic resolution

400 keV electrons yield a better relative image contrast than 100 keV electrons for a beam-sensitive organic crystal when spot-scan imaging is used [J. Brink and W. Chiu, J. Microscopy 161 (1991) 279]. A FORTRAN 77 program has been written to operate the spot-scan imaging system on a computer workstation under the VMS operating system which is interfaced serially to the JEOL4000 electron microscope. We demonstrate the application of this implementation by imaging crotoxin complex crystals embedded in either vitreous ice or glucose to 2.5 A resolution. The intensity strength of the structure factors of this protein crystal are different at low (> 10 A) resolution but similar at high resolution (< 10 A) for the two embedding media as expected from their scattering contrast difference. Based on our experience as judged from the electron diffraction patterns of highly tilted crystals, flat crystals embedded in glucose can be readily obtained. Furthermore, our spot-scan imaging system also has the option of correcting the focus gradient that is present in images of tilted specimens.

Crotoxin, a phospholipase A2 neurotoxin from snake venom, interacts with epithelial mammary cells, is internalized and induces secretion

Prolactin (PRL) induces liberation of arachidonic acid (AA) from phospholipids of lactating mammary epithelial cells and stimulates casein secretion. In order to investigate the possible involvement of phospholipase A2 (PLA2) activity in the hormonal control of casein secretion by PRL, we examined the effects of crotoxin, a PLA2 neurotoxin from snake venom, on mammary epithelial cells. Crotoxin is made of two subunits: a basic PLA2 with low toxicity (component B, CB) and an acidic, non-toxic and enzymatically inactive component A (CA) which enhances the pharmacological action of CB. While CA is inactive, the PLA2 subunit (CB) induces an accumulation of secretory products in the lumen of mammary acini, an extensive development of the Golgi apparatus. The secretion of newly synthesized casein is increased in the presence of CB and this effect is inhibited by nordihydroguaiaretic acid (NDGA) and caffeic acid, two inhibitors of the lipoxygenase pathway which also prevent stimulation of secretion by PRL. Further, CB transiently induces the release of radiolabelled AA from mammary tissues previously labelled with [14C]AA, the highest release being observed between 15 s and 5 min of contact with CB and CA. Immunofluorescence labelling by anti-CB antibodies of epithelial mammary tissues previously incubated with CA, CB or a combination of CA and CB indicates that CB binds to epithelial cells and is internalized, at least in part, and that CA enhances both CB binding and its internalization. These observations emphasize the involvement of PLA2 in the control of casein secretion and suggest that PLA2 acts intracellularly.

The complete sequence of the acidic subunit from Mojave toxin determined by Edman degradation and mass spectrometry

Mojave toxin, a heterodimeric, neurotoxic phospholipase complex from Crotalus scutulatus scutulatus, is one of a group of closely related rattlesnake toxins for which much structural information is still lacking. The complete amino-acid sequence of the acidic subunit from Mojave toxin was determined. The three individual peptide chains, derived from the acidic subunit by reductive alkylation, were separated by high-performance liquid chromatography. Fragmentations of the A and B chains were done using specific proteinases and the resulting peptide mixtures were fractionated by reverse-phase high-performance liquid chromatography. Sequence analyses on the intact chains and the fragments from digests were done by automated Edman degradation, carboxypeptidase Y degradation and triple-quadrupole and tandem-quadrupole Fourier-transform mass spectrometry. The sequence for each acidic subunit chain is very similar to the corresponding chain from the related neurotoxin complex, crotoxin, and overall the sequence is similar to the sequences of group I and II phospholipases A2. The N-terminus of the B chain is blocked by pyroglutamic acid. The existence of two distinct and closely related C chains was established. It is unlikely that the small sequence difference can account for the isoforms that are present in purified Mojave toxin and in unfractionated venom.

Electron imaging of crotoxin complex thin crystal at 3.5 A

Crotoxin complex forms thin crystals which are suitable for electron crystallographic analysis. We have used a 100 kV electron microscope equipped with a superconducting lens to image this crystal embedded in glucose. Optical diffraction analysis of the micrographs show unambiguously a structural resolution of 3.9 A which has not been obtained with the conventional microscope at room temperature. A density map with a nominal resolution of 3.5 A has been synthesized from these images by computer processing techniques.

Specimen preparative methods for electron crystallography of soluble proteins

Technical factors which influence the choice of specimen preparation method for electron crystallographic study of thin crystals of soluble proteins are discussed. Ice embedding appears to be the most desirable choice of preparation method. However, in terms of the yield of major structural information, we conclude that negative stain remains a useful method for low resolution and glucose embedding for high resolution.

Experimental strategy in three-dimensional structure determination of crotoxin complex thin crystal

Electron images and diffraction patterns of crotoxin complex thin crystals contain high-resolution structural information in projection at both room and low temperatures. This paper outlines our strategy for collecting three-dimensional amplitude and phase data from these uniquely well-ordered toxin thin crystals. Preliminary experiments in support of the feasibility of this approach are presented.