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Metalloproteomics analysis of iron and copper containing proteins in coastal and oceanic diatoms |
Over the past two years, we have examined the Fe and Cu requirements of four marine diatoms--two coastal and two oceanic--and the sensitivity of these diatoms to Fe and Cu limitation. Direct measurements of intracellular Cu levels revealed that the Cu demand of the phytoplankton species is inversely related to their respective cellular Fe requirements 1 . The oceanic isolates have extremely low Fe quotas but high metabolic demand for Cu, while the coastal isolates have high intracellular Fe but very low Cu quotas. These results suggest a possible replacement of Fe containing catalysts by Cu-containing ones in the oceanic species, and may explain the ability of oceanic diatoms to thrive with intracellular Fe levels insufficient for growth of their coastal counterparts. Our physiological studies suggest an interaction between Fe and Cu nutrition in marine phytoplankton. In order to fully resolve the biochemical and molecular basis for this, it is necessary to identify the dominant Fe and Cu containing metalloproteins in the cells, and examine their regulation by trace metal availability. Significant progress towards this goal has already begun following the recent completion of a number of genome sequencing projects in several marine phytoplankton species, including that of the coastal diatom, T. pseudonana . While some information about relative protein expression levels may be obtained from mRNA transcript quantity, mRNA levels may not necessarily correlate strongly with the corresponding activity or abundance of proteins. In addition, the function of the proteins may be greatly modified by post-translational modifications. Protemics on the other hand allows the direct quantification and identification of proteins present in an organisms or subcellular fraction under specific environmental conditions. The main goal of this project is to identify the dominant Fe and Cu containing proteins in a coastal and oceanic diatom ( T. pseudonana and T. oceanica ), and to study their regulation across a range of Fe and Cu limiting conditions. For this project, we are presently developing a novel technique for the purification and identification of cupro- and ferroproteins in collaboration with scientist at UBC and the USA.
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last updated October 28, 2004
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It is now firmly established that trace metals, in particular Fe, play an important role in regulating marine photosynthesis and biogeochemical cycles. Phytoplankton species isolated from low Fe, open ocean waters appear to have evolved a variety of mechanisms to enhance Fe acquisition from the environment, and minimize their cellular Fe requirements. The biochemical basis for the low Fe requirements of oceanic species remains unclear, but it has been suggested that other trace metals may play interactive roles in cellular Fe nutrition. For example, in yeasts and green algae, Cu appears to play an essential role in the high affinity Fe transport system, while the Cu-containing plastocyanin may substitute for the Fe-rich cytochrome c 6 in some green algae and cyanobacteria. The physiological and biochemical role of copper in other ecologically important phytoplankton, including diatoms, has thus far received very little research attention.