THE 1.5-ANGSTROM RESOLUTION CRYSTAL-STRUCTURE OF BACTERIAL LUCIFERASEIN LOW-SALT CONDITIONS

Bacterial luciferase is a flavin monooxygenase that catalyzes the oxid ation of a long-chain aldehyde and releases energy in the form of visi ble light. A new crystal form of luciferase cloned from Vibrio harveyi has been grown under low-salt concentrations, which diffract x-rays b eyond 1.5-Angstrom resolution. The x-ray structure of bacterial. lucif erase has been refined to a conventional R-factor of 18.2% for all rec orded synchrotron data between 30.0 and 1.50-Angstrom resolution, Bact erial luciferase is an alpha-beta heterodimer, and the individual subu nits fold into a single domain (beta/alpha)(8) barrel. The high resolu tion structure reveals a non-prolyl cis peptide bond that forms betwee n Ala(74) and Ala(75) in the alpha subunit near the putative active si te. This cis peptide bond may have functional significance for creatin g a cavity at the active site. Bacterial luciferase employs reduced fl avin as a substrate rather than a cofactor. The structure presented wa s determined in the absence of substrates. A comparison of the structu ral similarities between luciferase and a nonfluorescent flavoprotein, which is expressed in the lux operon of one genus of bioluminescent b acteria, suggests that the two proteins originated from a common ances tor. However, the flavin binding sites of the nonfluorescent protein a re likely not representative of the flavin binding site on luciferase. The structure presented here will furnish a detailed molecular model for all bacterial luciferases.