ATP-dependent Clp proteases in photosynthetic organisms - A cut above the rest!

Proteases are critical regulatory factors for many metabolic cellular proce sses as well as being vital for degrading proteins damaged during environme ntal stresses. Many of those responsible for targeted protein degradation r equire the hydrolysis of ATP, and one class that has attracted much attenti on recently are the Clp proteases. They are among the best characterized pr oteases to date, and were the first shown to rely on an ATPase regulatory s ubunit possessing molecular chaperone activity, which functions both within the proteolytic complex and independently. A range of Clp proteins has bee n identified from many different bacteria and eukaryotes, with by far the g reatest number and diversity of forms in oxygenic photobionts such as cyano bacteria and higher plants. Functionally, Clp proteins have also evolved in to one of the more critical proteolytic enzymes within photobionts, and it is now somewhat of a paradox that we currently know least about Clp proteas e functions in the photosynthetic organisms, where they have their most imp ortant roles. This discrepancy is now being addressed, with studies on Clp protein in cyanobacteria and, in an increasing number, in higher plants. (C ) 1999 Annals of Botany Company.