Structural insights into the A(1) ATPase from the archaeon, Methanosarcinamazei Go1

The low-resolution structure and overall dimensions of the A(3)B(3)CDF comp lex of the A(1) ATPase from Methanosarcina mazei Gol in solution is analyze d by synchrotron X-ray small-angle scattering. The radius of gyration and t he maximum size of the complex are 5.03 +/- 0.1 and 18.0 +/- 0.1 nm, respec tively. The low-resolution shape of the protein determined by two independe nt ab initio approaches has a knob-and-stalk-like feature. Its headpiece is approximately 9.4 nm long and 9.2 nm wide. The stalk, which is known to co nnect the headpiece to its membrane-bound A(o) part, is approximately 8.4 n m long. Limited tryptic digestion of the A(3)B(3)CDF complex was used to pr obe the topology of the smaller subunits (C-F). Trypsin was found to cleave subunit C most rapidly at three sites, Lys(20), LYs(21), and Arg(209), fol lowed by subunit F. In the A(3)B(3)CDF complex, subunit D remained protecte d from proteolysis.