General Trends in Trace Element Utilization Revealed by Comparative Genomic Analyses of Co, Cu, Mo, Ni, and Se

Trace elements are used by all organisms and provide proteins with unique coordination and catalytic and electron transfer properties. Although many trace element-containing proteins are well characterized, little is known about the general trends in trace element utilization. We carried out comparative genomic analyses of copper, molybdenum, nickel, cobalt (in the form of vitamin B-12), and selenium (in the form of selenocysteine) in 747 sequenced organisms at the following levels: (i) transporters and transport-related proteins, (ii) cofactor biosynthesis traits, and (iii) trace element-dependent proteins. Few organisms were found to utilize all five trace elements, whereas many symbionts, parasites, and yeasts used only one or none of these elements. Investigation of metalloproteomes and selenoproteomes revealed examples of increased utilization of proteins that use copper in land plants, cobalt in Dehalococcoides and Dictyostelium, and selenium in fish and algae, whereas nematodes were found to have great diversity of copper transporters. These analyses also characterized trace element metabolism in common model organisms and suggested new model organisms for experimental studies of individual trace elements. Mismatches in the occurrence of user proteins and corresponding transport systems revealed deficiencies in our understanding of trace element biology. Biological interactions among some trace elements were observed; however, such links were limited, and trace elements generally had unique utilization patterns. Finally, environmental factors, such as oxygen requirement and habitat, correlated with the utilization of certain trace elements. These data provide insights into the general features of utilization and evolution of trace elements in the three domains of life.