Mn₄Ca cluster shapes up

A new window on the structure of the metal cluster that splits water into O₂, H⁺, and electrons during photosynthesis should help those aiming to mimic nature's ability to harvest energy from the sun (Science 2006, 314, 821). Previous structural and spectroscopic studies have failed to nail down the structure of photosystem II's Mn₄Ca cluster. Johannes Messinger of Max Planck Institute for Bioinorganic Chemistry in Mülheim, Germany; Athina Zouni of the Technical University Berlin; and Vittal K. Yachandra of Lawrence Berkeley National Laboratory now provide a more satisfying snapshot of the cluster (shown in its protein environment; red balls = Mn, gray balls = bridging O, green ball = Ca). They obtained the structure by first using the protein's X-ray diffraction pattern to align a single crystal in an X-ray beam and then using X-ray absorption fine-structure spectroscopy to measure Mn-Mn and Mn-Ca vectors. The team plans to use the same method to probe subtle changes in the cluster during catalysis.