As an introduction to this lecture series on metal clusters in biology, we present the different families of natural metal centers. These may consist of one or more metal ions, sometimes supplemented by exogenous ligands (porphyrins, molybdopterin, cyanide, etc.) and attached by one or more coordination links to amino acids in the polypeptide chain. The most commonly used metals are iron and zinc, but nature also exploits less abundant metals such as molybdenum and cobalt.
The first lecture focuses on the large family of iron-sulfur clusters, which are the result of an organized assembly of iron and sulfur atoms, usually attached to the protein by bonds with cysteines in the polypeptide chain. These clusters play major roles in cellular metabolism in all living organisms: (i) electron transfer (respiration, photosynthesis, etc.); (ii) acid catalysis (aconitase); (iii) redox catalysis (S-adenosylmethionine reductolysis); (iv) regulation of gene expression (transcription and translation factors). These functional aspects are briefly discussed.
The second part of the lecture raises the question of the biosynthesis of these clusters. Iron and sulfur atoms do not spontaneously assemble in the host protein, and the establishment of the metal site depends on the action of highly complex biosynthetic protein machineries, which have only recently been identified and studied. The two main families of iron-sulfur cluster biosynthetic machineries, ISC and SUF, are presented in terms of their structure, function and regulation.
