Energy transduction in protein transport and the ATP hydrolytic cycle of SecA.
The motor protein SecA drives the transport of polypeptides through the ubiquitous protein channel SecYEG. Changes in protein-nucleotide binding energy during the hydrolytic cycle of SecA must be harnessed to drive large conformational changes resulting in channel opening and vectorial substrate polypeptide transport. Here, we elucidate the ATP hydrolysis cycle of SecA from Escherichia coli by transient and steady-state methods. The basal ATPase activity of SecA is very slow with the release of ADP being some 600-fold slower than hydrolysis. Upon binding to SecYEG the release of ADP is stimulated but remains rate-limiting. ADP release is fastest in the fully coupled system when a substrate protein is being translocated; in this case hydrolysis and ADP release occur at approximately the same rate. The data imply that ADP dissociation from SecA is accompanied by a structural rearrangement that is strongly coupled to the protein interface and protein translocation through SecYEG.
Robson
Alice
A
Department of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom.
Gold
Vicki A M
VA
Hodson
Skye
S
Clarke
Anthony R
AR
Collinson
Ian
I
D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D004735:Energy Transfer; D029968:Escherichia coli Proteins / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000378:metabolism; D011487:Protein Conformation; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins