Cross-talk between catalytic and regulatory elements in a DEAD motor domain is essential for SecA function.
SecA, the motor subunit of bacterial polypeptide translocase, is an RNA helicase. SecA comprises a dimerization C-terminal domain fused to an ATPase N-terminal domain containing conserved DEAD helicase motifs. We show that the N-terminal domain is organized like the motor core of DEAD proteins, encompassing two subdomains, NBD1 and IRA2. NBD1, a rigid nucleotide-binding domain, contains the minimal ATPase catalytic machinery. IRA2 binds to NBD1 and acts as an intramolecular regulator of ATP hydrolysis by controlling ADP release and optimal ATP catalysis at NBD1. IRA2 is flexible and can undergo changes in its alpha-helical content. The C-terminal domain associates with NBD1 and IRA2 and restricts IRA2 activator function. Thus, cytoplasmic SecA is maintained in the thermally stabilized ADP-bound state and unnecessary ATP hydrolysis cycles are prevented. Two DEAD family motifs in IRA2 are essential for IRA2-NBD1 binding, optimal nucleotide turnover and polypeptide translocation. We propose that translocation ligands alleviate C-terminal domain suppression, allowing IRA2 to stimulate nucleotide turnover at NBD1. DEAD motors may employ similar mechanisms to translocate different enzymes along chemically unrelated biopolymers.
Institute of Molecular Biology and Biotechnology, Medical School, University of Crete, PO Box 1527, GR-711 10 Iraklio, Crete, Greece.
G
G
Sianidis
S
S
Karamanou
E
E
Vrontou
K
K
Boulias
K
K
Repanas
N
N
Kyrpides
A S
AS
Politou
A
A
Economou
D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D020043:Genes, Essential / Q000235:genetics; D007700:Kinetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011993:Recombinant Fusion Proteins; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D013696:Temperature
D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; D000069816:SEC Translocation Channels; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins