Spinach chloroplast fructose-1,6-bisphosphatase: identification of the subtilisin-sensitive region and of conserved histidines

Abstract

Chloroplast fructose-1, 6-bisphosphatase (FbPase) is an essential enzyme in the photosynthetic pathway of carbon dioxide fixation into sugars. The properties of the chloroplast enzyme are clearly distinct from those of cytosolic gluconeogenic FbPases. Light-dependent activation via a ferredoxin/thioredoxin system and insensitivity to inhibition by AMP are unique characteristics of the chloroplast enzyme. However, preliminary acid sequence data (78 residues) have demonstrated that a significant degree of amino acid sequence similarity exists between spinach chloroplast and mammalian gluconeogenic frutose-1,6-bisphosphatase [Harrsch, P.B., Kim, Y., Fox, J. L., .times. Marcus, F. (1985) Biochem. Biophys. Res. Commun. 133, 520-526] In the present study, we have identified two stuctural features of spinanch chloroplast FbPase that appear to be common to all FbPases. These include (a) the presence of a protease-sensitive area located in a region equivalent to residues 51-71 of mammalin FbPases and (b) the recognation two conserved histidine residues, equivalent to histidines-253 and -311 of the mammalian eyznmes. In addition, we have obatiend sequence information accounting for more than three-fourths of the primary structure of spinach chloroplast FbPase. The high degree of homology observed between the chloroplast enzyme and gluconeogenic FbPase suggests a common evolutionary origin for all fructose-1,6-bisphosphatases in spite of their different functions and modes of regulation.