Roman A. Melnyk

Roman A. Melnyk

Associate Professor

BSc, Biochemistry, McMaster University co-op, 1993-1998
PhD, Biochemistry, University of Toronto, 1998-2004
Postdoc, Harvard Medical School, 2004-2006
Senior Scientist in Biology (Drug Discovery), Merck Frosst Canada, Merck & Co., 2006-2010

Lab Melnyk Lab
Office Phone 416-813-7654 ext. 328557

Research Description

Bacterial Toxin Pathogenesis: Molecular Mechanisms & Drug Discovery

Research Interests

  • Drug discovery
  • Bacterial pathogenesis
  • Structure & function of bacterial toxins
  • Biophysics of membrane protein transport
  • Membrane proteins

Research Activities

Bacterial protein toxins can play an important role in the establishment and propagation of numerous infectious diseases. The most potent toxins, including diphtheria, tetanus and anthrax toxins are multi-functional proteins that possess the remarkable ability to direct their own entry into cells through the formation of protein-conducting pores in the host membrane, through which the highly toxic enzymatic subunits traverse through. Since bacterial toxins are often solely responsible for the symptoms of many diseases, blocking their action on mammalian cells represents an attractive approach to potentially treat the symptoms of these devastating bacterial diseases. Using chemical biology and targeted drug discovery approaches combined with molecular biophysics and structural analysis we seek to identify and validate host & toxin targets and discover small molecule hits for further exploration and development. In addition, owing to the unique ability of these toxins to specifically and efficiently deliver their toxic enzymes into cells, an often insurmountable task for many protein-based drugs, we aim to develop toxin-delivery platforms to shuttle otherwise non-cell penetrant therapeutics into cells.

Awards & Distinctions

2014 — Early Researcher Award, Ontario Ministry of Economic Development & Innovation

Courses Taught

BCH2114 Frontiers in Drug Discovery
BCH479H1 Advanced Seminar in Biochemistry
BCH473Y Advanced Research Project in Biochemistry


Host-targeted niclosamide inhibits C. difficile virulence and prevents disease in mice without disrupting the gut microbiota.
Tam J, Hamza T, Ma B, Chen K, Beilhartz GL, Ravel J, Feng H, Melnyk RA.
Nat Commun. 2018 Dec 7;9(1):5233.

Intracellular Delivery of Human Purine Nucleoside Phosphorylase by Engineered Diphtheria Toxin Rescues Function in Target Cells.
Park M, Xu X, Min W, Sugiman-Marangos SN, Beilhartz GL, Adams JJ, Sidhu SS, Grunebaum E, Melnyk RA.
Mol Pharm. 2018 Nov 5;15(11):5217-522

Identification of a diphtheria toxin-like gene family beyond the Corynebacterium genus.
Mansfield MJ, Sugiman-Marangos SN, Melnyk RA, Doxey AC.
FEBS Lett. 2018 Aug;592(16):2693-2705

Direct detection of membrane-inserting fragments defines the translocation pores of a family of pathogenic toxins
Orrell KE, Tellgren-Roth Å, Di Bernardo M, Zhang Z, Cuviello F, Lundqvist J, von Heijne G, Nilsson I, Melnyk RA.
J Mol Biol. 2018 Sep 14;430(18 Pt B):3190-3199

A neutralizing antibody that blocks delivery of the enzymatic cargo of Clostridium difficile toxin TcdB into host cells.
Kroh HK, Chandrasekaran R, Zhang Z, Rosenthal K, Woods R, Jin X, Nyborg AC, Rainey GJ, Warrener P, Melnyk RA, Spiller BW, Lacy DB.
J Biol Chem. 2018 Jan 19;293(3):941-952

Identification of novel bifunctional HIV-1 reverse transcriptase inhibitors.
Lai MT, Tawa P, Auger A, Wang D, Su HP, Yan Y, Hazuda DJ, Miller MD, Asante-Appiah E, Melnyk RA.
J Antimicrob Chemother. 2018 Jan 1;73(1):109-117

Functional defects in Clostridium difficile TcdB toxin uptake identify CSPG4 receptor-binding determinants.
Gupta P, Zhang Z, Sugiman-Marangos SN, Tam J, Raman S, Julien JP, Kroh HK, Lacy DB, Murgolo N, Bekkari K, Therien AG, Hernandez LD, Melnyk RA.
J Biol Chem. 2017 Oct 20;292(42):17290-17301

Clostridium difficile toxins A and B: Receptors, pores, and translocation into cells.
Orrell KE, Zhang Z, Sugiman-Marangos SN, Melnyk RA.
Crit Rev Biochem Mol Biol. 2017 Aug;52(4):461-473.

Repurposing bacterial toxins for intracellular delivery of therapeutic proteins.
Beilhartz GL, Sugiman-Marangos SN, Melnyk RA.
Biochem Pharmacol. 2017 Oct 15;142:13-20.

Comment on "A small-molecule antivirulence agent for treating Clostridium difficile infection".
Beilhartz GL, Tam J, Zhang Z, Melnyk RA.
Sci Transl Med. 2016 Dec 21;8(370):370tc2

Crystal structure of Clostridium difficile toxin A.
Chumbler NM, Rutherford SA, Zhang Z, Farrow MA, Lisher JP, Farquhar E, Giedroc DP, Spiller BW, Melnyk RA, Lacy DB.
Nat Microbiol. 2016;1. pii: 15002

Small Molecules Take A Big Step Against Clostridium difficile.
Beilhartz GL, Tam J, Melnyk RA.
Trends Microbiol. 2015 Dec;23(12):746-748.

Efficient Delivery of Structurally Diverse Protein Cargo into Mammalian Cells by a Bacterial Toxin
Auger, A., Park., M., Nitschke, F., Minassian, L.M., Beilhartz, G.L., Minassian, B.A., Melnyk, R.A.
Mol Pharm, 2015; 12(8): 120-28

Small Molecule Inhibitors of Clostridium difficile Toxin B-Induced Cellular Damage
Tam, J., Beilhartz, G.L., Auger, A., Gupta, P., Therien, A.G., Melnyk, R.A.
Chem Biol, 2015; 19(22): 175-85

Derivatives of Mesoxalic Acid Block Translocation of HIV-1 Reverse Transcriptase
Bernatchez, J.A., Paul, R., Tchesnokov, E.P., Ngure, M., Beilhartz, G.L., Berghuis, A.M., Lavoie, R., Li, L., Auger, A., Melnyk. R.A., Grobler, J.A., Miller, M.D., Hazuda, D.J., Hecht, S.M., Götte, M.
J Biol Chem, 2015; 290(3): 1474-84

Translocation Domain Mutations Affecting Cellular Toxicity Identify the Clostridium difficile Toxin B Pore
Zhang, Z., Park, M., Tam, J., Auger, A., Beilhartz, G.L., Lacy, D. B., Melnyk, R.A.,
Proc Natl Acad Sci U S A. 2014 Mar 11;111(10):3721-6

Impact of Primer-Induced Conformational Dynamics of HIV-1 Reverse Transcriptase on Polymerase Translocation and Inhibition
Auger, A., Beilhartz, G.L., Zhu, S., Chauchon, E., Falgueyret, J.-P., Grobler, J.A., Götte, M. and Melnyk, R.A.
J Biol Chem. 2011 Aug 26;286(34):29575-83

A Loop Network within the Anthrax Toxin Pore Positions the Phenylalanine Clamp in an Active Conformation
Melnyk, R.A., and Collier, R.J.,
Proc Natl Acad Sci U S A. 2006 Jun 27;103(26):9802-7

Structural Determinants for the Binding of Anthrax Lethal Factor to Oligomeric Protective Antigen
Melnyk, R.A., Hewitt, K.M, Lacy, D.B., Lin, H.C., Gessner, C., Woods, V.L., Collier, R.J.,
J Biol Chem. 2006 Jan 20;281(3):1630-5

A Model of Anthrax Toxin Lethal Factor Bound to Protective Antigen
Lacy DB, Lin HC, Melnyk, R.A., Shueler-Furman O, Reither L, Cunningham K, Baker D, Collier RJ
Proc Natl Acad Sci U S A. 2005 Nov 8;102(45):16409-14

A Phenylalanine Clamp Catalyzes Translocation Through the Anthrax Toxin Pore
‡Krantz, B.A., ‡Melnyk, R.A., Zhang, S., Juris, S.J., Lacy D.B., Wu Z., Finkelstein, A., Collier, R.J., ‡ co-first author
Science 2005; 309(5735):777-781