LOW-RESOLUTION STRUCTURE OF THE TETRAMERIC PHENYLALANYL-TRANSFER RNA-SYNTHETASE FROM ESCHERICHIA-COLI - A NEUTRON SMALL-ANGLE SCATTERING STUDY OF HYBRIDS COMPOSED OF PROTONATED AND DEUTERATED PROTOMERS

Escherichia coli phenylalanyl-tRNA synthetase is a tetrameric protein composed of two types of protomers. In order to resolve the subunit organization, neutron small-angle scattering experiments have been performed in different contrasts with all types of isotope hybrids that could be obtained by reconstituting the α2β2 enzyme from the protonated and deuterated forms of the α and β subunits. Experiments have been also made with the isolated α promoter. A model for the α2β2 tetramer is deduced where the two α promoters are elongated ellipsoids (45 X 45 X 160 Å3) lying side by side with an angle of about 40° between their long axes and where the two β subunits are also elongated ellipsoids (31 X 31 X 130 Å3) with an angle of 30° between their axes. This model was obtained by assuming that the two pairs of subunits are in contact in an orthogonal manner and by taking advantage of the measured distance between the centers of mass of the a2 and β2 pairs (d = 23 ± 2 A). © 1990, American Chemical Society. All rights reserved.