ULTRA HIGH RESOLUTION STRUCTURE OF A NOVEL TRANSFERASE ENZYME

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This novel transferase enzyme catalyzes the transfer reactions of small groups. We have determined the crystal structure of a novel transferase enzyme using MAD phasing techniques, and refined it to 1.5 ¿ resolution. Analysis of the structure revealed a hitherto unknown octameric structure of this class of enzymes with interesting interactions between the individual subunits. It is also noteworthy that this enzyme shows complex reaction kinetics. Therefore, an ultra high resolution of the enzyme is valuable for a proper understanding of the reaction mechanism. In this study we focused on the data collection of the enzyme with a covalently bound inhibitor. The complex crystallized with a triclinic unit cell. The crystals diffracted to better than 1.0 ¿ and we collected a 1.0 ¿ data set with 80% overall completion and an Rsym of 3.8%. The I/sig(I) for the highest resolution shell (1.04 ¿ ¿ 1.00 ¿) is 4.3 sigma. The current refinement at 1.25 ¿ provided valuable information about the mode of catalysis for this novel enzyme. A hydrophobic channel created by the oligomeric structure restricts the access to the active site. This channel provides very specific ractions kenitics and explains the novel property of the enzyme. The structural study proposes similar properties for other oligomeric enzymes in this family.