Structural and Functional Studies of Diiron Carboxylate Proteins

• Iron is essential to all life; it is a vital component of many proteins in humans as well as plants and bacteria. Because of the ability of iron to activate oxygen, it is often found in proteins that interact with oxygen in some way. One of the protein families that utilize iron to harness the oxidative power of the oxygen molecule for different purposes is the diiron carboxylate protein family. These proteins have two iron ions bound in the active site that are coordinated by four carboxylic residues and two histidines. These enzymes catalyse reactions such as radical generation, ubiquinol oxidation, fatty acid desaturation, iron oxidation and many different hydroxylation reactions. One subgroup of this protein family that recently has been discovered contains the membrane-bound diiron carboxylate proteins. In this thesis we have studied three diiron carboxylate proteins. The first, alternative oxidase, is a membrane-bound ubiquinol oxidase present in the respiratory chain of plants, some yeasts and protozoa. We have obtained the first spectroscopical evidence for the presence of a diiron carboxylate site in alternative oxidase. We have also identified the first prokaryotic alternative oxidase and shown it to be expressed and functional. The second membrane-bound diiron carboxylate protein studied is Coq7; the inactivation of this protein has been reported to prolong the life span of the model organism Caenorhabditis elegans. We have shown that Coq7 catalyses a hydroxylation in the biosynthesis of ubiquinone and identified it as a diiron carboxylate protein. Finally we have solved the structure of the ribonucleotide reductase R2 subunit from Chlamydia trachomatis, a soluble diiron carboxylate protein. We have discovered that this is an unusual member of the R2 family because it challenges the generally accepted dogma of a conserved radical-harbouring tyrosine being a requirement for enzyme activity in this protein class. We have by EPR spectroscopy demonstrated that the radical in this protein is stored as a high-valent species at the diiron site instead of on a tyrosine. We also found that many organisms, including several human pathogens, have R2 proteins with the same sequence abnormalities and propose that these proteins constitute a new ribonucleotide reductase subclass, class Ic.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinsk bioteknologi -- Medicinsk bioteknologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Medical Biotechnology -- Medical Biotechnology (hsv//eng)

Nyckelord

Biochemistry

Biokemi

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