Modular Protein Ligation: A New Paradigm as a Reagent Platform for Pre-Clinical Drug Discovery.

Significant resource is spent by drug discovery project teams to generate numerous, yet unique target constructs for the multiple platforms used to drive drug discovery programs including: functional assays, biophysical studies, structural biology, and biochemical high throughput screening campaigns. To improve this process, we developed Modular Protein Ligation (MPL), a combinatorial reagent platform utilizing Expressed Protein Ligation to site-specifically label proteins at the C-terminus with a variety of cysteine-lysine dipeptide conjugates. Historically, such proteins have been chemically labeled non-specifically through surface amino acids. To demonstrate the feasibility of this approach, we first applied MPL to proteins of varying size in different target classes using different recombinant protein expression systems, which were then evaluated in several different downstream assays. A key advantage to the implementation of this paradigm is that one construct can generate multiple final products, significantly streamlining the reagent generation for multiple early drug discovery project teams.

Expression, purification, and characterization of an enzymatically active truncated human rho-kinase I (ROCK I) domain expressed in Sf-9 insect cells.

Rho Kinase I (ROCK I) is a serine/threonine kinase that is involved in diverse cellular signaling. To further understand the physiological role of ROCK I and to identify and develop potent and selective inhibitors of ROCK I, we have overexpressed and purified a constitutively active dimeric human ROCK I (3-543) kinase domain using the Sf9-baculovirus expression system. In addition, using a limited proteolysis technique, we have identified a minimal functional subdomain of ROCK I that can be used in crystallization studies. The availability of multimilligram amounts of purified and well characterized functional human ROCK I kinase domains will be useful in screening and structural studies.

Development of a cell-based high throughput luciferase enzyme fragment complementation assay to identify nuclear-factor-e2-related transcription factor 2 activators.

Nuclear-factor-E2-related transcription factor 2 (Nrf2) regulates a large panel of Phase II genes and plays an important role in cell survival. Nrf2 activation has been shown as preventing cigarette smoke-induced alveolar enlargement in mice. Therefore, activation of the Nrf2 protein by small-molecule activators represents an attractive therapeutic strategy that is used for chronic obstructive pulmonary disease. In this article, we describe a cell-based luciferase enzyme fragment complementation assay that identifies Nrf2 activators. This assay is based on the interaction of Nrf2 with its nuclear partner MafK or runt-related transcription factor 2 (RunX2) and is dependent on the reconstitution of a "split" luciferase. Firefly luciferase is split into two fragments, which are genetically fused to Nrf2 and MafK or RunX2, respectively. BacMam technology was used to deliver the fusion constructs into cells for expression of the tagged proteins. When the BacMam-transduced cells were treated with Nrf2 activators, the Nrf2 protein was stabilized and translocated into the nucleus where it interacted with MafK or RunX2. The interaction of Nrf2 and MafK or RunX2 brought together the two luciferase fragments that form an active luciferase. The assay was developed in a 384-well format and was optimized by titrating the BacMam concentration, transduction time, cell density, and fetal bovine serum concentration. It was further validated with known Nrf2 activators. Our data show that this assay is robust, sensitive, and amenable to high throughput screening of a large compound collection for the identification of novel Nrf2 activators.