Ping Li (2015-2016)
Assistant Professor, Department of Chemistry
Kansas State University

Engineering Human NRMT1 for its Substrate Profiling

NRMT1 is a newly discovered protein methyltransferase that has been suggested to play important roles in oncogenesis and progression of several major cancers. Additionally, it is overexpressed in patients with colon cancers and the level increases as the cancer advances. This proposal aims to engineer NRMT1 to profile its substrates so that the roles of NRMT1 in tumorigenesis can be revealed.

Methylation is a commonly observed protein posttranslational modification that plays important roles in a variety of signaling pathways and epigenetic regulation. Defects in the methylation have been demonstrated to cause various major cancers. Protein methylation is catalyzed by protein methyltransferases (PMTs) using S-adenosyl-L-methionine (SAM) as the methyl donor. So far, three classes of PMTs have been discovered, which include protein lysine methyltransferases (PKMTs), protein arginine methyltransferases (PRMTs), and protein N-terminus methyltransferases. While mechanisms and functions of PKMT and PRMT have been studied in detail, knowledge of protein N-terminus methyltransferases is largely unexplored. The α-N-terminal RCC1 methyltransferase (NRMT, now renamed as NRMT1) discovered in 2010 is the first eukaryotic protein N-terminus methyltransferase, which methylates proteins containing a N-terminal sequence consisting of MXPK. Upon the cleavage of end methionine, the N-terminal α-NH2 is methylated to form mono-, di-, and
trimethylated products. Based on the conserved sequence, more than 300 human proteins have been predicted to be NRMT1 substrates, in which ~40 proteins are related to cancers. Four of them have been validated in vitro, which includes SET, retinoblastoma protein (Rb), damaged DNA-binding protein 2 (DDB2), and RCC1. These validated NRMT1 targets are known to be involved in the oncogenesis and progression of various cancers. Additional NRMT1 substrates such as centromere protein A (CENP-A) that do not contain the conserved sequence have also been discovered. Dysfunction of the CENP-A are linked to colon cancers.

In addition, NRMT1 is found to overexpress in patients with colon cancers and the level of expression increases as the cancer progresses. Thus, NRMT1 may serve as a new therapeutic target or biomarker of cancers. The ultimate goal of this research is to characterize the roles of NRMTs (including isoforms of
NRMT1 and NRMT2) and α-N-methylation in maintaining the normal cellular states so that their links with cancers can be revealed. The current one-year pilot proposal will focus on engineering NRMT1 to identify its substrates using modified SAM analogs and click-chemistry.