Conformation of Escherichia coli ribosomal protein L7/L12 in solution: hydrodynamic, spectroscopic, and conformation...

The conformation of Escherichia coli ribosomal protein L7/L12 in solution has been studied using spectroscopic and hydrodynamic methods. Circular dichroism studies in the near-ultraviolet region reveal two bands at 262 and 268 nm originating from the tertiary conformational environment of the phenylalanyl residues. Additional characterization of the phenylalanine environment includes an intrinsic fluorescence emission spectrum arising from the phenylalanine fluorophores. Computer analysis of the far-ultraviolet circular dichroism spectrum suggests that L7/L12 contains as much as approximately 76% alpha helix. Hydrodynamic properties of L7/L12, measured with the purpose of providing relevant shape information, include the frictional coefficient ratio (1.84 +/- 0.03) and intrinsic viscosity (28 +/- 0.4 mL/g). The experimentally determined frictional coefficient (6.15 +/- 0.15 X 10(-8) has been compared with theoretical calculations of the same value employing two independent methods and assuming various dimensions for the L7/L12 dimer. Combining the experimental results from this work with those available from the literature, and using conformation predictive methods of Chou & Fasman [P. Y. Chou & G. D. Fasman (1974) Biochemistry 13, 211-222, 222-245] and of Maxfield & Scheraga (F. R. Maxfield & H. A. Scheraga (1976) Biochemistry 15, 5138-5153), several possible molecular models of the L7/L12 dimer have been constructed and critically examined. A model which is consistent with all of the available data is proposed.