HIGH-RESOLUTION STRUCTURE OF AN ENGINEERED CRO MONOMER SHOWS CHANGES IN CONFORMATION RELATIVE TO THE NATIVE DIMER

A rationally designed, genetically engineered, monomeric form of the C ro protein from bacteriophage lambda has been crystallized and its str ucture determined by isomorphous replacement and refined to a resoluti on of 1.54 Angstrom. The structure confirms the rationale of the desig n but, at the same time, reveals 1-2 Angstrom shifts throughout the mo nomer structure relative to the previously determined structure of the dimeric wild-type protein. These changes include a 1.6 Angstrom main- chain shift in part of the beta-sheet region of the molecule relative to the alpha-helical region and a 1.1 Angstrom shift of a buried pheny lalanine within the core as well as a correlated 2.2 Angstrom shift in a solvent-exposed beta-hairpin. The conformational adjustments appear to reflect an inherent flexibility of the protein that is associated with its DNA-binding function.