 |
Todd Holyoak
Assistant Professor |
|---|
University of Waterloo, Ontario, Canada, B.Sc, 1994
University of Notre Dame, Notre Dame, Indiana, Ph.D., 2000
Rosenstiel Basic Medical Research Center, Brandeis University, Waltham, MA,
Postdoctoral Fellow,
2000 - 2004
As a result of catalyzing the hydrolysis of the amide backbone of protein
substrates proteases are important determinants of the structure and function of
many proteins and therefore extremely important in the regulation of many
physiological processes. The importance of understanding the catalytic and bi
ological
functions of proteases becomes evident if we consider that genes for
endoproteases comprise approximately 2% of the human genome and 1-5% of the
genomes of infectious agents such as bacteria and viruses.
In biology proteases have been shown to be involved in processes as
divergent as digestion, aging, cancer, cell signaling and anthrax toxicity, to
name a few. It is clear that
we have just begun to scratch the surface of understanding the importance of
proteases in biology and disease.
While proteases are thought to be one of the best studied
classes of enzymes, only a hand full of enzymes are represented in these studies
with many of the well characterized enzymes being degradative enzymes as
represented by trypisn and chymotrypsin. The
catalytic mechanism of these serine proteases is well understood.
Unlike many of the degradative enzymes, the proteases involved in
biological function and disease are highly selective for their protein
substrates and have been relatively unstudied at the mechanistic level.
As a result, little knowledge exists of their substrate selectivity and
the mechanisms by which it is generated.
Research in my lab is focused upon determining the mechanisms of catalysis and substrate selectivity in families of highly selective proteases. Our primary experimental tool for addressing this question is X-ray crystallography. This is complemented by other biochemical and biophysical techniques in order to make the correlation between enzyme structure and function. Currently we are studying three enzyme systems.
1)
Kex2/Pro-protein convertase family
Members of this
family are known virulence factors in pathogenic fungi, and homologues in higher
eukaryotes play important roles not only in homeostatic functions but also in
disease states including cancer, Alzheimer’s and anthrax toxicity.
With the observation of both redundant and non-redundant activities of
these enzymes in vivo we are
interested in structurally and mechanistically characterizing this family of
proteases to determine the structural determinants of their high degree of
selectivity for their biologically and medically important protein substrates.
2)
Mycosin protease family
Initial
experiments have demonstrated that the mycosins are a family of exported
proteases that are membrane and cell wall-associated and are shed into the
culture supernatant, typical of virulence factors in bacterial pathogens.
Preliminary characterization of this family of enzymes suggests that they bear
some resemblance to the Kex2 family of subtilases. We are interested in
characterizing the proteolytic activity of these enzymes and determining their
substrate selectivity and the role they play in the pathogenesis of tuberculosis
infection.
3)
IgA protease family
Immunoglobin A proteases are a family of secreted proteases that are produced by pathogenic strains of Haemophilus, Neisseria and Streptococcus that are the causative agents of such diseases as gonorrhea and bacterial meningitis. These enzymes cleave human secretory IgA1 in the hinge region of the heavy chain, inactivating the molecule and allowing the bacteria to circumvent host defenses mediated by IgA1 in the mucosal linings. We are very interested in the extreme substrate selectivity exhibited by this family of enzymes, which includes both serine and metallo-endoproteases.
