Characterization of soluble artificial proteins with random sequences

The structural and catalytic properties of two soluble random proteins, RP3-42 and RP3-45, of 141 amino acid residues were investigated. Although no marked secondary structure was detected by CD spectrum, sedimentation equilibrium and small-angle X-ray scattering studies showed that they form an oligomeric structure and are as compact as the molten globule. The random proteins have low but distinct esterase activity; the values of the second-order rate constant for the hydrolysis of p-nitrophenol were 0.78 and 1.39 M(-1) s(-1) for RP3-42 and RP3-45, respectively. The differences in the properties of the random and the native proteins are discussed from the evolutionary point of view.