TI  - The rates of commitment to renaturation of <prot>rhodanese</prot> and <prot>glutamine synthetase</prot> in the presence of the groE chaperonins.
PG  - 29598-601
AB  - Current models of chaperonin-assisted folding suggest that proteins
      undergo multiple rounds of binding and release before they are released in
      a form that is committed to folding to the native state. Using
      immunoprecipitation techniques, we have determined the rates at which
      <prot>rhodanese</prot> and <prot>glutamine synthetase</prot> (<prot>GS</prot>) are released from <prot>groEL</prot> in a form
      committed to refold to active enzyme.  <prot>Rhodanese</prot>  and  <prot>glutamine synthetase</prot> 
      were chosen as substrates because they exhibit different solution
      requirements for the chaperonin system and they form stable &quot;folding
      arrested&quot; complexes with   <prot>groEL</prot>  . At various times during the groE-dependent
      renaturations, <prot>groEL</prot> was rapidly removed from the renaturation mixture by
      immunoprecipitation and centrifugation (30 s). The conformers that are
      committed to the native state remained in the supernatant and were assayed
      after 1 h. At 25 degrees C, the rate profiles indicate the release and
      commitment to folding of <prot>GS</prot> to its native state occurs far earlier (t1/2 &lt;
      1 min) than for <prot>rhodanese</prot> (t1/2 = 5 min). In light of previous results, it
      appears that  <prot>GS</prot>  monomers can attain a groE-independent assembly competent
      conformation after a brief interaction with the  chaperonin . In contrast,
      the renaturation rate for <prot>rhodanese</prot> with the groE chaperonins mirrored the
      committed renaturation rates following <prot>groEL</prot> depletion. This suggests that
       <prot>rhodanese</prot>  must interact with  <prot>groEL</prot>  throughout most of its folding reaction
      before it acquires a folding competent (groE independent) state. If
      current models of chaperonin mechanism are correct, <prot>rhodanese</prot> undergoes
      more rebinding and release cycles than does <prot>GS</prot>. Structurally, the degree
      of cycling and hence the rate of commitment to folding to the active form
      are probably dictated by the hydrophobic nature, number, and lifetimes of
      the folding intermediates that interact with the chaperonins.
AD  - Department of Biochemistry and Molecular Biology, University of Kansas
