ANAHEIM, Calif. -- One of life's simplest organisms -- a mud-dwelling photosynthetic bacterium -- is helping scientists unlock the complex structural makeup that occurs when proteins come together to perform important biological duties.
Such knowledge, says Klaus Schulten of the University of Illinois, can shed light on what happens when proteins aggregate (combine and arrange) at the right time and when they do it at the wrong time, as is the case in diseases of the central nervous system such as Alzheimer's disease and bovine spongiform encephalopathy (Mad Cow Disease).
Speaking at the annual meeting of the American Association for the Advancement of Science, Schulten told how his theoretical biophysics group at the U. of I. Beckman Institute for Advanced Science and Technology combined X-ray crystallography and computational modeling to identify the structure of a protein called the two light-harvesting complex in the purple bacteria Rhodobacter sphaeroides. The protein is an aggregate of eight independent but identical units that form a highly symmetrical ring. A similar protein forms a ring of 16 units and surrounds the bacterium's photosynthetic reaction center.
The whole ensemble contains hundreds of chlorophylls as well as carotenoids, both of which are light-absorbing compounds that serve to harvest sunlight and funnel its energy to the centrally located reaction center.
Schulten, who holds the U. of I. Swanlund Chair in Physics, his Beckman Institute colleagues and collaborators of the Max Planck Institute for Biochemistry in Frankfort, Germany, first published their three-dimensional rendering in the May 1996 issue of the journal Structure. Subsequent accomplishments, including the creation of a colorful physical model of the photosynthetic center, based on the computer model, have been published in physics and biological journals and in the Proceedings of the National Academy of Sciences.