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

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Abstract
The conformation of E. coli ribosomal protein L7/L12 in solution was studied using spectroscopic and hydrodynamic methods. Circular dichroism studies in the near UV region reveal 2 bands at 262 and 268 nm originating from the tertiary conformational environment of the phenylalanyl residues. Additional chracterization of the phenylalanine environment includes an intrinsic fluorescence emission spectrum arising from the phenylalanine fluorophores. Computer analysis of the far UV circular dichroism spectrum suggests that L7/L12 contains as much as .apprx. 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 .+-. 0.4ml/g). The experimentally determined frictional coefficient (6.15 .+-. 0.15 .times. 10-8) was compared with theoretical calculations of the same value employing 2 independent methods and assuming various dimensions for the L7/L12 dimer. Combining this and other experimental results and using conformation predictive methods, several possible molecular models of the L7/L12 dimer were constructed and critically examined. A model which is consistent with all of the available data is proposed.