STRUCTURAL STUDIES ON THE 2.25-MDA HOMOMULTIMERIC PHOSPHOENOLPYRUVATESYNTHASE FROM STAPHYLOTHERMUS-MARINUS

The phosphoenolpyruvate synthase of the hyperthermophilic archaeon Sta phylothermus marinus forms an unusually large homomultimeric complex o f 93 kDa subunits. Electron image analysis of negatively stained and l ow-dose unstained preparations showed that the complex has a single, s table characteristic view and a well-preserved core with threefold rot ational symmetry. The periphery of the assembly is composed of a nebul ous, possibly flexible, component. Mass measurements by scanning trans mission electron microscopy yielded a molecular weight of 2250 +/- 230 kDa, confirming the well-defined nature of the structure and indicati ng that it is composed of 24 +/- 2.5 subunits. The stability and symme try of the characteristic projection views suggest a polyhedral three- dimensional architecture. The novel quaternary arrangement of this enz yme might be a consequence of its adaptation to an extreme environment . (C) 1996 Academic Press, Inc.