The correct expression and assembly of multisubunit proteins (oligomers) and monomers containing multidomain structures depends on the cell's ability to prevent inappropriate aggregation and misfolding of newly synthesized polypeptides. In recent years, experimental evidence has accumulated which suggests that protein factors, termed molecular chaperonins, aid in this process by preventing detrimental aggregation through transient binding events. The exact molecular details involved in both the recognition and release of bound polypeptides are unknown at present. One set of molecular chaperonins found in E. coli have been identified as intrinsic heat shock proteins (expression levels increase during heat stress). These components have homologous counterparts in eucaryotic mitochondrial systems and are absolutely required by the cell. This past year's work has examined the chaperonin facilitated renaturation and reassociation of dodecameric E. coli glutamine synthetase (GS). This protein reassociation reaction was used to establish a potential model system in order to study the interactions between the chaperonin components and potential protein refolding or folding systems. The interaction of one chaperonin component, GroEL (also called Chaperonin-60 or Cpn6O) prevents the association of unfolded GS monomers until ATP is added to the reconstitution mix. Under near-physiological solution conditions, GS activity regain is only 20-30% of the original activity IN THE ABSENCE OF GorEL. When refolding of GS is initiated IN THE PRESENCE OF GroEL, 70 TO 80% OF THE ORIGINAL ACTIVITY RETURNS. The second component, GroES, does not seem to be required to facilitate the renaturation of GS, in vitro. Based on the available evidence, GroEL appeared to intervene at the kinetic rather than the thermodynamic level.
