Small‐Angle X‐Ray and Light‐Scattering Study of Native and Trypsin‐Modified Methionyl‐tRNA Synthetase from Escherichia coli

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Abstract
Small‐angle X‐ray scattering experiments were performed on an absolute scale on solutions of methionyl‐tRNA synthetase from Escherichia coli in its native and trypsin‐modified forms. A light‐scattering study was performed on the same solutions to verify monodispersity.The structural parameters for the trypsin‐modified enzyme, radius of gyration (2.48 nm), volume (90 nm3), surface/volume (1.5 nm−1) and the distribution of chords can account for an equivalent prolate ellipsoid of revolution having an axial ratio 2.3 and a maximum length of 9 nm, with a creviced surface.The results obtained for the native enzyme [i.e. radius of gyration (4.3 nm), volume (244 nm3), distribution of the scattering intensity and distribution of chords] exclude the possibility of a very compact quaternary structure and suggest that the enzyme consists of at least two globular parts, probably the two protomers, linked together by interactions involving a limited region of the structure.

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