THE STRUCTURAL AND BIOCHEMICAL CHARACTERIZATION OF DEUBIQUITINATING ENZYMES LOTA AND UCHL1 R178Q

The Deubiquitinating (DUB) enzymes, LotA and UCHL1 R178Q, were examined biochemically and also structurally in the case of UCHL1 R178Q. LotA is a bacterial effector of Legionella pneumophila that enables the pathogen to establish a replicative niche. LotA has two Deubiquitinase (DUB) domains specific to different substrates. Here, I report biochemical examinations the first DUB domain that is specific to Lys6-linked di-ubiquitin. Michaelis- Menten kinetic parameters were determined for this domain. Through activity assays of various truncations a series of residues were discerned that contribute to interaction of the distal binding site of ubiquitin chain.

UCHL1 mutant R178Q displays enhanced activity when compared to wild type (WT). The mutant was crystallized for structural analysis to gain insights into the higher catalytic activity of the mutant. The structure revealed that the catalytic histidine maintains a misaligned orientation similar to the WT enzyme. Biochemical analysis was done to ascertain the role of key residues that interact with the catalytic histidine. The residue type at position 178 in the structure plays a key role in enhancing the enzyme activity.