The conformational changes that the GroEL oligomer undergoes upon nucl
eotide and cochaperonin GroES binding have been studied using electron
microscopy and image processing techniques. Average side views of the
three allosteric states (TT, TR, and RR, which correspond to none, on
e, or both of the two heptameric rings of the GroEL oligomer occupied
by nucleotide, respectively) of GroEL and GroEL-GroES complexes for AD
P, ATP, and two nonhydrolyzable analogs (AMP-PNP and ATP gamma S) have
been obtained at 20-25 Angstrom resolution. Both AMP-PNP and ATP indu
ce similar conformational shifts in the apical domains of GroEL, At th
e TR state, only one of the GroEL rings shows an upward and outward mo
vement of the apical domains (''open state''). At the RR state for AMP
-PNP and ATP, both GroEL rings undergo conformational changes, albeit
of different magnitude, giving rise to a structurally asymmetric parti
cle (one ring in the ''open'' state, while the other is in an ''interm
ediate'' state). These changes are also observed when GroEL is incubat
ed with ADP and P-i, but not with ADP, which suggests that upon ATP bi
nding, GroEL undergoes a conformational change that is partly maintain
ed after ATP hydrolysis and as long as ADP and P-i are bound to the Gr
oEL ring. The conformational changes undergone by GroEL are discussed
within the framework of a proposed GroEL cycle mechanism. (C) 1997 Aca
demic Press.