SHIJINA.A BCH 10-05- 04 S2 MSc BIOCHEMISTRY ABZYMES SHIJINA.A BCH 10-05- 04 S2 MSc BIOCHEMISTRY

Introduction Antibodies and enzymes share the ability to bind with compounds with great specificity and high affinity. This property has been exploited in the development of antibodies with catalytic activity. Antibodies have been 1st characterized as proteins produced by the IS for binding with molecules called antigens. One basic difference between antibodies and enzymes is that the former binds the complementary structure in its ground state , while enzymes bind in high energy state

In 1986 , the 1st monoclonal catalytic antibodies termed abzymes against a chemically stable analog of the transition state of a reaction were obtained Abzymes are catalytic antibodies having structural complementarity for the transition state of an enzyme catalyzed reaction. They bind strongly to the transition state with high association constant, enhancing the reaction rate . Abzymes reduce rotational entropy .

Sources of Abzymes Abzymes are usually artificial constructs. They also obtained from human and animal serum. Found in normal humans and ii patients with autoimmune diseases. These are capable of hydrolyzing proteins, DNA, RNA, polysaccharides etc

Protabzymes and DNA Abzymes Natural abzymes with proteolytic activity are called Protabzymes .e.g.: hydrolysis of specific proteins in patients with autoimmune diseases such as bronchial Asthma ,multiple sclerosis. DNA hydrolyzing activity are called DNA abzymes. The pathogenic role of DNA abzymes is not quite clear. However they act as a powerful regulator of apoptosis.

Production of abzymes Antibody molecules are produced by the immune system to bind and neutralize foreign substances called antigens Foreign proteins of bacteria , viruses and some chemical molecules called haptens , act as antigens . Transition state analogs are molecules which are more stable than the transition state itself , but they mimic its 3D structure .

If injected into the blood stream of an animal , transition state analogs act as haptens and elicit antibody production. Abs are isolated from the serum of the animal and used as abzymes . Theoretically ,if the Ab binds to a transition state molecule, it may be expected to catalyze a corresponding chemical reaction by forcing substrates into transition state geometry.

Transition state Substrate Pdt mice Transition state analog Ab complementary to transition state (act as Ag)

Examples for abzymes Hydrolysis of hydroxy ester by abzymes Hydroxy ester forms a cyclic intermediate during hydrolysis. Cyclic phosphonate ester is the structural analog of the cyclic intermediate. This analog is used as an antigen to elicit antibodies. These antibodies bind the cyclic intermediate , increasing the reaction rate .

Hydroxy ester Cyclic intermediate δ-lactone phenol Anti –cyclic intermediate antibody (Abzymes) Cyclic phosphonate ester (antigen) ,mimic cyclic intermediate

Hydrolysis of ester by abzymes Ester forms a tetrahedral intermediate during hydrolysis The phosphate analog of ester mimic this intermediate, used as antigen to elicit antibodies. These antibodies recognize and bind to tetrahedral intermediate and stabilize it resulting in rate acceleration.

Biosynthesis of Heme It involves introduction of Fe2+ into protophorphyrine by ferrochelatase. This process is called metallation Metallation involves the distortation of pyrole ring by 36ºto create a bent transition state

This state is apt for the entry Fe2+ Methyl mesoporphyrin , an analog of the bent transition state , is used as antigen to elicit abzymes. These abzymes bind the bent transition state and distorts the porphyrin facilitating metallation rate 2500fold higher

Reactions catalyzed by Abzymes Amide hydrolysis Trans- Esterification photo cleavage Photodimerization Decarboxylation Oxidation Cyclization Reduction of diketone Hydrolysis of enol ethers

Applications Synthesis of simple organic molecules Drug development Treat Cancer Treat allergy treat viral and bacterial infection

Reference Enzymology –T. Devasena

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