Structure of ribosomal protein L30 from Thermus thermophilus at 1.9 angstrom resolution: conformational flexibility of the molecule

The crystal structure of ribosomal protein L30 from the extreme thermophili c bacterium Thermus thermophilus has been determined at 1.9 Angstrom resolu tion. The crystals are trigonal and belong to space group P3(2)21, with uni t-cell parameters a = b = 63.5, c = 77.8 Angstrom, a = beta = 90, gamma = 1 20 degrees and two molecules per asymmetric unit. The structure was solved by the molecular-replacement method with AMoRe and refined with X-PLOR to a n R value of 20.3% and an R-free of 25.3 % in the resolution range 8-1.9 An gstrom. Detailed analyses of the structures of the two molecules in the asy mmetric unit and comparison of T. thermophilus L30 structure with the struc ture of homologous L30 from Bacillus stearothermophilus reveal two flexible regions at opposite ends of the rather elongated molecule. Such flexibilit y could be important for the protein fitting in the ribosome. A comparison with B. stearothermophilus L30 shows a higher number of salt bridges and un bound positively charged residues and an increased accessible hydrophobic a rea on the surface of T, themrophilus L30. This could contribute to the sta bility of both the extreme thermophile protein and the ribosome as a whole.