with Dr. Brian Martin (National Institute of Mental 
Health). 
Comparison of the primary structures showed im- 
portant similarities among these peptides and with 
that of NTX and charybdotoxin. Functional charac- 
terization of the newly purified peptides was carried 
out by binding displacement experiments using rat 
brain synaptosomes and radiolabeled NTX. Both 
toxins from C. I. limpidus displace 50% of mem- 
brane-bound NTX at the level of 100 pM. Further 
experiments conducted with cerebellum granule 
cells, using the patch-clamp whole-cell configura- 
tion technique, showed that these peptides are capa- 
ble of blocking one type of channel present in 
this preparation. 
Cloning of Scorpion Toxin Genes 
from Centruroides Venomous Glands 
A cDNA library was prepared from venomous 
glands of C. noxius scorpions. The Agtll library 
was probed with specific oligonucleotides chosen 
from known amino acid sequences of Na^ channel- 
blocking toxins from scorpions of the genus Cen- 
truroides. Among several positive clones carrying 
toxin genes, four were selected and their nucleotide 
sequences determined. A comparative analysis of 
these sequences with one of reported scorpion tox- 
ins revealed that these cDNAs code for a family of 
very similar toxins. One of the clones corresponded 
to toxin 11-10 of C. noxius; the others are closely 
related to toxin 1 from C. noxius and variant 3 from 
C. sculpturatus. Southern blot genomic analysis 
showed a minimum size of ~600 bp as an EcoKl 
fragment for elements of this family. 
Polymerase chain reaction (PCR) amplifications 
of C. noxius genomic DNA, and hybridization of 
PCR products with specific probes, indicated that 
the genomic structural regions that code for the 
toxin-cloned genes do not contain introns. Compari- 
son of these nucleotide sequences with those of 
cDNAs that code for North African scorpion toxins 
revealed that they share common features. It seems 
that this family of genes evolved from an ancestral 
gene that has experienced several duplications, and 
each duplicated gene has evolved independently by 
means of insertions, deletions, and point mutations. 
Dr. Possani is Professor and Chairman of the 
Department of Biochemistry at the Biotechnology 
Institute, National Autonomous University of 
Mexico, Cuernavaca. 
Article 
Zamudio, F., Saavedra, R., Martin, B.M., Gurrola- 
Briones, G., Herion, P., and Possani, L.D. 1992. 
Amino acid sequence and immunological charac- 
terization with monoclonal antibodies of two tox- 
ins from the venom of the scorpion Centruroides 
noxius Hoffmann. Eur f Biochem 204:281-292. 
PROTEIN CRYSTALLOGRAPHY IN THE STUDY OF INFECTIOUS DISEASES 
Randy J. Read, Ph.D., International Research Scholar 
The research in Dr. Read's laboratory is aimed at 
advancing the understanding of infectious diseases 
at the molecular level, using information from the 
three-dimensional structures of key proteins. There 
are two major aspects to this work. First, the x-ray 
crystal structures of a number of proteins involved 
in pathogenesis are being determined. Second, com- 
putational techniques are being developed to ex- 
ploit such structural information in the rational de- 
sign of new drugs for the treatment of infectious 
diseases. 
Bacterial Toxins 
Many pathogenic bacteria produce toxins that 
cause cell and tissue damage and can be responsible 
for the most severe effects of the illness. Bacterial 
toxins often have an A-B structure in which the B 
(binding) subunit binds to the surface of a target 
cell and the A (active) subunit enters the cell, carry- 
ing out the toxic action. Two such toxins are being 
studied: verotoxin-1 (with Dr. James Brunton, Uni- 
versity of Toronto) and pertussis toxin (with Dr. 
Glen Armstrong, University of Alberta, and with 
Connaught Laboratories in Toronto) . 
The Shiga toxin family is a group of closely related 
toxins, including Shiga toxin, produced by Shigella 
dysenteriae type 1 , and verotoxins (VTs) , produced 
by certain strains of Escherichia coli. Shiga toxin is 
associated with bacterial dysentery, a serious prob- 
lem in many developing countries. The strains of E. 
coli that produce VTs cause a disease often referred 
to as "hamburger disease," because it can be ac- 
quired from contaminated hamburger. VTs can pro- 
voke the hemolytic uremic syndrome and are 
INTERNATIONAL RESEARCH SCHOLARS 527 
