Protein Crystallography in the Study 
of Infectious Diseases 
Randy J. Read, Ph.D. — International Research Scholar 
Dr. Read is Assistant Professor of Medical Microbiology and Infectious Diseases and of Biochemistry at the 
University of Alberta, Edmonton. He obtained his undergraduate and doctoral training in the Department 
of Biochemistry at the University of Alberta, then pursued postdoctoral training in protein crystallography 
with Wim Hoi at the University of Groningen in the Netherlands, before returning to Edmonton. 
INFECTIOUS organisms — viruses, bacteria, and 
parasites — must overcome many obstacles to 
cause disease. They must gain entry to their fa- 
vored niche in the host, obtain nutrients, evade 
attacks of the immune system, and spread to new 
hosts. These are complex problems with com- 
plex and varied solutions. But the pathogenic 
mechanisms used by microorganisms to infect 
and cause disease are gradually coming to light, 
in some cases at the level of the key molecules. 
The interest in pathogenesis is more than aca- 
demic, since the understanding of these pro- 
cesses can be exploited to prevent or treat disease. 
Our interest is in advancing the understanding 
of infectious disease at the molecular level, using 
the technique of x-ray crystallography to study 
the three-dimensional structure of important 
proteins. There are two major aspects to our 
work. We are studying the crystal structures of a 
number of proteins that are involved in pathogen- 
esis, some of which are described below, and we 
are developing methods to exploit this kind of 
structural information in the design of new drugs. 
Bacterial Toxins 
Many pathogenic bacteria produce toxins that 
cause cell and tissue damage and can be responsi- 
ble for the most severe effects of the illness. Bacte- 
rial toxins often belong to the A-B class, having a 
two-part structure in which the B (binding) sub- 
unit binds to the surface of a target cell and the A 
(active) subunit enters the cell, carrying out the 
toxic action. We are involved in studying the 
crystal structures of pertussis toxin (in collabora- 
tion with Glen Armstrong at the University of Al- 
berta, and with Connaught Laboratories in To- 
ronto) and verotoxin (in collaboration with 
James Brunton, University of Toronto). 
Pertussis toxin (PT) is produced by Bordetella 
pertussis, the bacterium that causes whooping 
cough. There is a major interest in the role of this 
toxin in improved vaccines. Currently, killed 
whole-cell vaccines are used for whooping 
cough. They are effective, but have an undesir- 
able level of toxicity. The side effects should be 
reduced or eliminated in a defined vaccine pro- 
duced from genetically engineered proteins. It has 
been shown that PT is a necessary component of 
effective whooping cough vaccines, but it must be 
rendered nontoxic for safe use. A three-dimensional 
structure of PT would help show how to remove its 
toxicity while preserving the surface features of the 
molecule recognized by the immune system. In ad- 
dition, we would gain a better understanding of how 
the B component of the toxin recognizes the surface 
of target cells, how the A subunit enters the cell, and 
how it carries out its toxic action. Exploiting the 
intense radiation produced by synchrotrons, we 
have collected x-ray data from crystals of this toxin 
and from several potential heavy-atom derivatives, 
but the determination of the phases needed for the 
visualization of the structure is still in progress. 
The Shiga toxin family is a group of closely re- 
lated toxins produced by Shigella dysenteriae 
type 1 (Shiga toxin) and by certain strains of Esch- 
erichia coli (verotoxins, or VTs). Shiga toxin is 
associated with bacterial dysentery, a serious 
problem in many developing countries. The 
strains of E. coli that produce VTs cause a disease 
often referred to as "hamburger disease," be- 
cause it can be acquired from contaminated ham- 
burger. VTs can provoke the hemolytic uremic 
syndrome and are thereby the major cause of 
acute kidney failure in children. 
We have crystallized and solved the structure 
of the B subunit of VT-1 , a member of the Shiga 
toxin family. The B subunit forms a pentamer that 
recognizes target cell surfaces by binding to the 
carbohydrate component of a cell-surface glyco- 
lipid, globotriaosylceramide (Gbj). Since this in- 
teraction largely determines which cells the 
toxin will attack, we are interested in under- 
standing its molecular details. Comparison of the 
amino acid sequences of all the toxins in this fam- 
ily has enabled us to predict that a surface cleft 
between B-subunit monomers will prove respon- 
sible for binding. Crystallographic binding stud- 
ies should allow us to test this prediction. 
The most surprising result is an unexpected 
structural similarity to the B subunit of members 
of the cholera toxin family. This is unexpected 
because the associated A subunits of the two 
toxin families are completely unrelated, the B 
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