SecB modulates the nucleotide-bound state of SecA and stimulates ATPase activity.
In Escherichia coli, the formation of SecA-SecB complexes has a direct effect on SecA ATPase activity. The mechanism of this interaction was evaluated and defined using controlled trypsinolysis, equilibrium dialysis at low temperature, and kinetic analyses of the SecA ATPase reaction. The proteolysis data indicate that SecB and the nonhydrolyzable ATP analogue AMP-P-C-P induce similar conformational changes in SecA which result in a more open or extended structure that is suggestive of the ATP-bound form. The effect is synergistic and concentration-dependent, and requires the occupation of both the high- and low-affinity nucleotide binding sites for maximum effect. The equilibrium dialysis experiments and kinetic data support the observation that the SecB-enhanced SecA ATPase activity is the result of an increased rate of ATP hydrolysis rather than an increase in the affinity of ATP for SecA and that the high-affinity nucleotide binding site is conformationally regulated by SecB. It appears that SecB may function as an intermolecular regulator of ATP hydrolysis by promoting the ATP-bound state of SecA. The inhibition of SecA ATPase activity by sodium azide in the presence of IMVs and a functional signal peptide further indicates that SecB promotes the ATP-bound form of SecA.
Miller
Alexander
A
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA.
Wang
Ligong
L
Kendall
Debra A
DA
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001665:Binding Sites; D003956:Dialysis; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism; D029968:Escherichia coli Proteins; D006868:Hydrolysis; D007700:Kinetics; D008081:Liposomes; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008969:Molecular Sequence Data; D021381:Protein Transport; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D019810:Sodium Azide / Q000494:pharmacology; D014357:Trypsin / Q000378:metabolism
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008081:Liposomes; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D000255:Adenosine Triphosphate; D019810:Sodium Azide; D014357:Trypsin; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins