Expected Year of Graduation: 2017
Research Lab: Prof. Nicolas Silvaggi
Major Area of Focus: Biochemistry
Minor Area of Focus: Organic Chemistry

Thesis: Structure-Function Relationships in Bacterial Regulatory Proteins and an Enzyme Involved in Antibiotic Biosynthesis

Previously Attended

Bachelor’s degree of Science in Soochow University

Master’s degree of Bioengineering in Shandong University

Why I like Chemistry

It’s more detailed to explore and understand the essence of biological processes

Why I chose the Chemistry and Biochemistry Program at UW-Milwaukee

I like crystallography, which is an important tool to determine protein structures. Dr. Silvaggi Lab is working on many proteins (like ADC family, RitR) and exploring the mechanisms based on their structure and enzyme kinetics. In this lab, I can learn how to crystallize proteins and determine their structures by X-ray diffraction

Favorite things to do in Milwaukee

Hiking and BBQ in beautiful parks.

Research Goals

My work spans two important areas of biochemistry: enzyme catalysis and regulation of gene expression by DNA-binding proteins. The first part of my work is a mechanistic enzymology project aimed at understanding the structure and mechanism of the novel pyridoxal-5’-phosphate (PLP)-dependent L-arginine hydroxylase/deaminase, MppP, fromStreptomyces wadayamensis (SwMppP). The enzyme SwMppP is a critical component of many antibiotics with potent activity against drug-resistant pathogens like MRSA. SwMppP is predicted to be a type I/II aminotransferase based on primary sequence identity. However, NMR and ESI-MS results showed that SwMppP is not an aminotransferase, but rather a hydroxylase. This is exciting because SwMppP is the first PLP-dependent enzyme to react with oxygen in any context other than oxidative decarboxylation.

The second part is focused on a new family of two-component response regulator proteins that lack the catalytic aspartate residue that mimics the phosphorylation mechanism of typical 2-component response regulators. These so-called aspartate-less receiver domain (ALR) proteins are not regulated by phosphorylation, but by other factors such as binding of a ligand. We are using biophysical tools to determine the regulatory mechanisms of proteins with redox-sensitive ALR domains. RitR from Streptococcus pneumonia R6, plays roles in regulating iron uptake, oxidative stress response, and pathogenicity in a mouse lung model. Our structure showed that N53 takes the place of the phosphorylatable aspartate residue of typical response regulators, and the Mg²⁺-binding site required for phosphorylation is disrupted in RitR. Thus, RitR is certainly not regulated by phosphorylation of the receiver domain, which means that RitR must necessarily have a different activation mechanism.

Publications

1. Zhu Y, Han L, Hefferon KL, Sivaggi NR, Wilson DB, McBride MJ. Periplasmic Cytophaga hutchinsonii endoglucanases are required for use of crystalline cellulose as sole carbon and energy source. Applied and Environmental Microbiology. 2016, 82 (15): 4835-4845
2. Han L, Schwabacher AW, Moran GR, Silvaggi NR.Streptomyces wadayamensis MppP is a PLP-Dependent L-Arginine α-deaminase, γ-Hydroxylase in the Enduracididine Biosynthetic Pathway. Biochemistry. 2015, 54: 7029−7040
3. Maule AF, Wright DP, Weiner JJ, Han L, Peterson FC, Volkman BF, Silvaggi NS, Ulijasz AT. The aspartate-less receiver (ALR) domains: distribution, structure and function. PLOS Pathogens. 2015, 11(4): e1004795
4. Guthrie ML, Sidhu PS, Hill EK, Horan TC, Nandhikonda P, Teske KA, Yuan NY, Sidorko M, Rodali R, Cook JM, Han L, Silvaggi NR, Bikle DD, Moore RG, Singh RK, Arnold LA. Antitumor Activity of 3-Indolylmethanamines 31B and PS121912. Anticancer Research. 2015, 35(11): 6001-6007
5. Teske K, Nandhikonda P, Bogart JW, Feleke B, Sidhu P, Yuan N, Preston J, Goy R, Han L, Silvaggi NR, Singh RK, Bikle DD, Cook JM, Arnold LA. Identification of VDR antagonists among nuclear receptor ligands using virtual screening. Nuclear Receptor Research. 2014, 1. pii: 101076
6. Sidhu PS, Teske K, Feleke B, Yuan NY, Guthrie ML, Fernstrum GB, Vyas ND, Han L, Preston J, Bogart JW, Silvaggi NR, Cook JM, Singh RK, Bikle DD, Arnold LA. Anticancer activity of VDR-coregulator inhibitor PS121912. Cancer Chemotherapy Pharmacology. 2014, 74(4): 787-798
7. Zhang X, Hu S, Du X, Li T, Han L, Kong J. Heterologous expression of carcinoembryonic antigen in Lactococcus lactis via LcsB-mediated surface displaying system for oral vaccine development. Journal of Microbiology, Immunology, and Infection. 2016, 49(6): 851-858
8. Hu S, Kong J, Sun Z, Han L, Kong W, Yang P. Heterologous Protein Display on the Cell Surface of Lactic Acid Bacteria Mediated by the S-Layer Protein. Microbial Cell Factories 2011, DOI: 10.1186/1475-2859-10-86

Poster Presentations