Mak A. Saito, Matthew R. McIlvin, Dawn M. Moran, Tyler J. Goepfert, Giacomo R. DiTullio, Anton F. Post, and Carl H. Lamborg
Marine primary productivity is strongly influenced by the scarcity of required nutrients, yet our understanding of these nutrient limitations is informed by experimental observations with sparse geographical coverage and methodological limitations. We developed a quantitative proteomic method to directly assess nutrient stress in high-light ecotypes of the abundant cyanobacteriumProchlorococcus across a meridional transect in the central Pacific Ocean. Multiple peptidebiomarkers detected widespread and overlapping regions of nutritional stress for nitrogen and phosphorus in the North Pacific Subtropical Gyre and iron in the equatorial Pacific. Quantitativeprotein analyses demonstrated simultaneous stress for these nutrients at biome interfaces. This application of proteomic biomarkers to diagnose ocean metabolism demonstratedProchlorococcus actively and simultaneously deploying multiple biochemical strategies for low-nutrient conditions in the oceans.
A complex iron-calcium cofactor catalyzing phosphotransfer chemistry
Shee Chien Yong, Pietro Roversi, James Lillington, Fernanda Rodriguez, Martin Krehenbrink, Oliver B. Zeldin, Elspeth F. Garman, Susan M. Lea, Ben C. Berks
Alkaline phosphatases play a crucial role in phosphate acquisition by microorganisms. To expand our understanding of catalysis by this class of enzymes, we have determined the structure of the widely occurring microbial alkaline phosphatase PhoX. The enzyme contains a complex active-site cofactor comprising two antiferromagnetically coupled ferric iron ions (Fe3 +), three calcium ions (Ca2 +), and an oxo group bridging three of the metal ions. Notably, the main part of the cofactor resembles synthetic oxide-centered triangular metal complexes. Structures of PhoX-ligand complexes reveal how the active-site metal ions bind substrate and implicate the cofactor oxo group in the catalytic mechanism. The presence of iron in PhoX raises the possibility that iron bioavailability limits microbial phosphate acquisition.