THE PHOTOSYNTHETIC CHROMATOPHORE

点击翻译按钮获取中文摘要

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The chromatophore is a pseudo-organelle that is responsible for harvesting light and subsequent conversion of light energy to chemical energy in the form of ATP (http://www.ks.uiuc.edu/Research/psures). After initial excitation from photon absorption by the light harvesting proteins in the chromatophore, excitation energy is tranferred in a multi-step process to a reaction center (RC). At the RC the excitation energy is used to charge a quinone molecule, which then diffuses through the protein-rich chromatophore membrane to a bc$_1$. There the charged quinone is oxidized to produce a proton gradient across the membrane, which in turn drives ATP production by ATP synthase. In purple bacteria, such as Rhodobacter sphaeroides, the protein responsible for photon capture are known as light harvesting complex 1 (LH1) and light harvesting complex 2 (LH2). LH1 associates with two other proteins found in the chromatophore, RC and PufX, to form LH1- RC-PufX dimer complexes. LH2 and LH1-RC-PufX have a dual function; not only are they responsible for capturing light energy, they also induce membrane curvature to shape the chromatophore into, e.g., vesicles or tubes. Therefore, the systemis relevant to understand two fundamental questions in biophysics, namely membrane morphonegensis and cellular energy production.