Fast closure of N-terminal long loops but slow formation of β strands precedes the folding transition state of Escherichia coli adenylate kinase.
The nature of the earliest steps of the initiation of the folding pathway of globular proteins is still controversial. To elucidate the role of early closure of long loop structures in the folding transition, we studied the folding kinetics of subdomain structures in Escherichia coli adenylate kinase (AK) using Förster type resonance excitation energy transfer (FRET)-based methods. The overall folding rate of the AK molecule and of several segments that form native β strands is 0.5 ± 0.3 s(-1), in sharp contrast to the 1000-fold faster closure of three long loop structures in the CORE domain. A FRET-based "double kinetics" analysis revealed complex transient changes in the initially closed N-terminal loop structure that then opens and closes again at the end of the folding pathway. The study of subdomain folding in situ suggests a hierarchic ordered folding mechanism, in which early and rapid cross-linking by hydrophobic loop closure provides structural stabilization at the initiation of the folding pathway.
The Goodman Faculty of Life Sciences, Bar Ilan University , Ramat Gan, Israel 52900.
Tomer
T
Orevi
Eldad
E
Ben Ishay
Sivan Levin
SL
Gershanov
Mayan Ben
MB
Dalak
Dan
D
Amir
Elisha
E
Haas
D000263:Adenylate Kinase / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology*; D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D008956:Models, Chemical; D017510:Protein Folding; D017433:Protein Structure, Secondary
D000263:Adenylate Kinase