Crystallization and preliminary X-ray diffraction analysis of the catalytic subunit of ADP-glucose pyrophosphorylase from potato tuber

ADP-glucose pyrophosphorylase is the key regulatory enzyme in the biosynthe sis of starch in plants and glycogen in bacteria. The enzyme from potato tu ber is comprised of a regulatory subunit and a catalytic subunit and is pre sent as a heterotetramer (alpha(2)beta(2)) The catalytic subunit from potat o tuber (50 kDa) was crystallized in four different forms, two of which are suitable for structural studies. A tetragonal crystal form obtained in the presence of the substrate analog Cr-ATP diffracted to 2.2 Angstrom and bel ongs to space group P4(1) (or its enantiomorph), with unit-cell parameters a = b = 110.57, c = 190.14 Angstrom. A second crystal form obtained diffrac ted to 2.8 Angstrom and belongs to space group PZ, with unit-eel parameters a = 80.06, b = 138.84, c = 92.20 Angstrom, beta = 112.40 degrees. As this protein displays no significant homology to any currently known protein str ucture, a search for heavy-atom derivatives has been initiated.