13] Structure-function relationships in metalloproteins

Abstract

This chapter discusses the structure–function relationships in metalloproteins. Metalloproteins represent a diverse class of biological macromolecules that perform a wide array of physiologic functions. These functions include the conversion of light into chemical energy in photoreceptors, electron transport, small molecule transport and storage, structural organization of protein matrices, small molecule sensing, and the synthesis/degradation of various metabolites. As iron and copper are the most abundant of the transition metals in biological molecules, Fe/Cu-containing proteins and enzymes provide a good cross-section of the diversity of function of metalloproteins. Iron-containing proteins and enzymes generally fall into two categories: heme and nonheme iron proteins. Heme proteins are one of the most widely distributed metalloproteins in nature. Nonheme iron proteins include oxygen carriers (hemerythrins) and electron transport proteins (ferredoxins and iron-sulfur proteins containing Fe 4 S 4 , Fe 2 S 2 , and Fe 3 S 4 centers). A number of other proteins bind Fe for transport and storage. The optical properties of the heme group as well as the fact that the heme group is either the sole active site or one of the active sites of the protein have proven to be an extraordinarily useful probe for monitoring structure-function relationships in a wide variety of heme proteins.