Research Interests:

We are interested in the biogenesis and function of protein complexes in energy-transducing membranes. In particular, we studytwo pigment-protein complexes, Photosystem I (PSI) and Photosystem II (PSII), in the thylakoid membranes in cyanobacteria andplants. Both PSI and PSII convert solar energy into biologically usable chemical energy. PSII catalyzes the production of molecularoxygen from water. We use Synechocystis 6803, a unicellular cyanobacterium as a microbial model system to study PSII.

Synechocystis 6803 cells are naturally transformable with exogenous DNA. Moreover, it is the first photosynthetic organism, thegenome of which has been completely sequenced. The life-history of PSII is intriguing. As an inevitable consequence of itsfunction, PSII is damaged, and D1, one of its protein components, is rapidly turned over. We are using molecular approaches to study the biogenesis of PSII. We have identified the gene encoding CtpA, a C-terminal processing protease involved in one of the terminal steps in this process. We are currently pursuing biochemical and genetic approaches to dissect the function of this novel protease. For our studies on PSI, we use both Synechocystis and Anabaena, a filamentous cyanobacterium. The latter organism can grow in complete darkness, a useful property, since most of the PSI mutants are extremely light-sensitive. Recently, we have created site-specific mutations in PsaC, a small protein in PSI, that coordinates two iron-sulfur clusters. Optical and magnetic resonance spectroscopic techniques are being used to determine the effects of such mutations on electron transport through PSI.

Mn is an important cofactor in PSII. We have identified a cluster of genes that encode components of a high-affinity ABC transporter complex for Mn in Synechocystis, the first of its kind in any organism. Transporters of this family are found in microbes to men, and many of them are key determinants in a number of human diseases. Various biochemical and genetic techniques are being used to study this transporter complex for Mn, an essential element for the survival of any organism.

Keywords:

mutagenesis, photosynthesis, membrane proteins, protein turnover, Mn transport