6 Substrate Analog Inhibitors of Highly Specific Proteases
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JAMES BURTON Massachusetts General Hospital and Harvard Medical School, Boston, M A 02114
Highly specific proteolytic enzymes cleave a single peptide bond in a naturally occurring substrate. These proteases appear to be integral parts of many biologic processes and may be contrasted with less specific proteases isolated from the gastrointestinal tract. Peptides modeled on the amino acid sequence around the cleavage site of the substrate frequently inhibit the enzyme and provide a starting point for the development of therapeutically relevant drugs which can block a single biologic process. The development of inhibitors for renin, k a l l i k r e i n , and IgA protease demonstrates the applicability of the substrate analog approach to drug design. 1
Proteolytic enzymes which s p l i t a single peptide bond in a specific amino acid sequence are integral parts of many biologic processes (J_). These highly specific proteases may be contrasted with the less specific, but more intensively studied, enzymes from the gastrointestinal tract which cleave peptide bonds linking many types of amino acids. Examples of highly specific proteases (Table I) are: renin which cleaves angiotensinogen to i n i t i a t e generation of the pressor agent angiotensin II ( 2 ) ; the kallikreins which produce either the hypotensive peptides k a l l i din or bradykinin from kininogen ( 3 ) ; IgA-| protease which inactivates human secretory immunoglobulin by cleavage of a peptide bond i n the hinge region ( 4 ) ; various members of the complement and clotting cascades (5,65"; and proteases important in the maturation of viruses (7). Hypertension, shock, infection by both bacteria and viruses, clotting disorders, and immune system dyscrasias could be treated by selective inhibition of the highly specific proteases which are components of these disorders. Highly specific proteases appear to cleave substrates by the same mechanisms used by more general proteases. Serine proteases, metaloproteases, and aspartyl proteases with greatly restricted s p e c i f i c i t y have been identified. Specificity appears to reside i n the architecture of the active site rather than i n functional groups which hydrolyze the peptide bond. 0097-6156/ 84/ 0251 -0137S06.00/ 0 © 1984 American Chemical Society
Vida and Gordon; Conformationally Directed Drug Design ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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CONFORMATIONALLY DIRECTED DRUG DESIGN
Downloaded by NORTH CAROLINA STATE UNIV on December 30, 2017 | http://pubs.acs.org Publication Date: April 24, 1984 | doi: 10.1021/bk-1984-0251.ch006
Table I.
Action of Some Highly Specific Proteases
Protease
Substrate
Renin
Angiotensinogen
Kallikrein
JgAl Protease
Kininogen
Secretory IgA1
Sequence Cleaved
DRVYIHPFHLVIH-
-SLMKRPPGFSPFRSSR-
-TPE^TPSPS-TPPTPSPS-
Action
Produce Angiotensin I
Produce Kallidin
Inactivate Secretory IgA-j
t Highly specific proteases may bind peptides which are homologous with the amino acid sequence of the naturally occurring substrate around the cleavage s i t e . These peptides, which are termed substrate analog Inhibitors (8), competitively block highly specific proteases. Presumably the substrate analog i n h i b i tors can assume the conformation necessary to f i t into i n the enzyme active s i t e . These synthetic analogs of the naturally occurring substrate may be contrasted with other proteins and peptides which usually do not bind to highly specific proteases. The use of substrate analogs has led to the rapid development of inhibitors for several highly specific proteases. Research from this laboratory on the development of renin inhibitors, k a l l i k r e i n inhibitors, and inhibitors of IgA
