Harnessing calcineurin-FK506-FKBP12 crystal structures from invasive fungal pathogens to develop antifungal agents.


Calcineurin is important for fungal virulence and a potential antifungal target, but compounds targeting calcineurin, such as FK506, are immunosuppressive. Here we report the crystal structures of calcineurin catalytic (CnA) and regulatory (CnB) subunits complexed with FK506 and the FK506-binding protein (FKBP12) from human fungal pathogens (Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans and Coccidioides immitis). Fungal calcineurin complexes are similar to the mammalian complex, but comparison of fungal and human FKBP12 (hFKBP12) reveals conformational differences in the 40s and 80s loops. NMR analysis, molecular dynamic simulations, and mutations of the A. fumigatus CnA/CnB-FK506-FKBP12-complex identify a Phe88 residue, not conserved in hFKBP12, as critical for binding and inhibition of fungal calcineurin. These differences enable us to develop a less immunosuppressive FK506 analog, APX879, with an acetohydrazine substitution of the C22-carbonyl of FK506. APX879 exhibits reduced immunosuppressive activity and retains broad-spectrum antifungal activity and efficacy in a murine model of invasive fungal infection.





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Publication Info

Juvvadi, Praveen R, David Fox, Benjamin G Bobay, Michael J Hoy, Sophie MC Gobeil, Ronald A Venters, Zanetta Chang, Jackie J Lin, et al. (2019). Harnessing calcineurin-FK506-FKBP12 crystal structures from invasive fungal pathogens to develop antifungal agents. Nature communications, 10(1). p. 4275. 10.1038/s41467-019-12199-1 Retrieved from https://hdl.handle.net/10161/28886.

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Benjamin Bobay

Assistant Professor in Radiology

I am the Assistant Director of the Duke University NMR Center and an Assistant Professor in the Duke Radiology Department. I was originally trained as a structural biochemist with an emphasis on utilizing NMR and continue to use this technique daily helping collaborators characterize protein structures and small molecules through a diverse set of NMR experiments. Through the structural characterization of various proteins, from both planta and eukaryotes, I have developed a robust protocol of utilizing computational biology for describing binding events, mutations, post-translations modifications (PTMs), and/or general behavior within in silico solution scenarios. I have utilized these techniques in collaborations ranging from plant pathologists at the Swammerdam Institute for Life Sciences department at the University of Amsterdam to biomedical engineers at North Carolina State University to professors in the Pediatrics department at Duke University. These studies have centered around the structural and functional consequences of PTMs (such as phosphorylation), mutation events, truncation of multi-domain proteins, dimer pulling experiments, to screening of large databases of ligands for potential binding events. Through this combination of NMR and computational biology I have amassed 50 peer-reviewed published articles and countless roles on scientific projects, as well as the development of several tutorials concerning the creation of ligand databases and high-throughput screening of large databases utilizing several different molecular dynamic and computational docking programs.


Ronald Venters

Assistant Professor in Radiology

I am Director of the Duke University NMR Center and a faculty member in the Duke Radiology Department (https://radiology.duke.edu/faculty/divisions/research-admin/). I have over 35 years of experience in the structure determination and dynamics of large biological macromolecules and in NMR methods development.  I am actively involved with training investigators in these areas and in assisting them with their projects.


Maria Ciofani

Associate Professor of Integrative Immunobiology

Transcriptional Regulation of Proinflammatory Lymphocytes

IL-17-expressing CD4 T helper (Th17) cells are important members of the intestinal immune cell community that contribute to protection against bacterial and fungal infections, and maintenance of intestinal homeostasis.  Although central to immunity, dysregulted Th17 cell function has been implicated in tissue inflammation and autoimmune disease (e.g. Inflammatory bowel disease, arthritis, and multiple sclerosis).  In order to understand this balance between healthy and pathogenic responses, we are interested in defining the transcriptional regulatory mechanisms that govern (1) Th17 cell specification from naive T cell precursors and, (2) Th17 cell effector plasticity during inflammation.  Combining genome-wide interrogation of regulatory information (transcription factor occupancy, chromatin accessibility, and transcriptional output) with gene-deficiency models in mice, we can dissect the contribution of key transcriptional regulators in proinflammatory T cell function.

We currently have open positions for students, postdoctoral fellows and a research technician.


Leonard D. Spicer

University Distinguished Service Professor Emeritus

The focus of this laboratory is the study of structure/function relationships in biological macromolecules and their binding interactions. The principal method we use for system characterization is magnetic resonance spectroscopy. One specific area of interest is the structural characterization of functional domains in proteins which regulate the transcription of DNA coding for biosynthetic enzymes. The system under current investigation is the methionine repressor protein metJ, its corepressor S-adenosylmethionine, and the cognate sequence DNA. This protein, which functions as a dimer, exhibits a recently described DNA binding motif involving insertion of two beta strands into the major groove with additional stabilization of the complex arising from helix contacts at the dimer-dimer interface. We are using a full complement of heteronuclear 3D and 4D NMR methods to aid in the assignment of the main chain of the metJ repressor. We have recently reported a thermodynamic analysis of the binding interactions of metJ with its cognate DNA and corepressor SAM. We are now developing methods to measure fast proton exchange rates to complement our planned solution structural characterization. We have just initiated another project in collaboration with scientists at the Pacific Northwest National Laboratory to study macromelecular structures of DNA repair proteins in the nucleotide excision repair pathway. The first components of this critical supramacromolecular assembly we are investigating involve the DNA binding domain of the XPA protein for which we are determining the global fold in solution by NMR. Our program also includes a systematic approach to characterizing the conformational preferences of a number of sequentially related peptides developed by Dr. Barton Haynes' laboratory as candidate vaccines for HIV. The peptides consist of a fusion of two noncontiguous segments of the HIV protein gp120. Our goal is to establish whether structural conformers in solution contribute to peptide immunogenicity. We have finished a careful conformational analysis of the initial four peptides and are now correlating the conformer similarities and differences with immunogenic properties. We have also rationally designed several new peptides based on structural criteria and corresponding structural homology to the heavy fragment of IgA proteins. Initial NMR analysis and immunogenic response to three of the designed mutants indicate the rational design of preferred conformers was successful, but raised some novel questions regarding function of immunogenic peptides. We have also just begun a study of solution conformations of the hypoglycosylated tumor specific epitope repeat unit of human mucin and a promising mutant identified by Dombrowski and Wright. This epitope is common to breast and other adenocarcinomas and regulation of tumor specific lymphoid cells responding to this immunogen may be an important step in tumor control. Another protein under investigation is a functional core packing mutant of thioredoxin. We have fully characterized backbone chain dynamics to assess the impact of this mutation on molecular motions and are currently determining its high resolution tertiary structure. Currently, we are also using this mutant to demonstrate a new approach to global fold determination using a minimum set of long range NMR constraints. Finally, as an essential part of these studies, we are developing and have reported new 3- and 4-dimensional NMR experiments and heteronuclear filters for application to large protein systems and binding complexes.

Finally, the core activities of the NMR Center staff have continued to progress rapidly and enhancements to the state-of-the-art instrumentation have again been incorporated. A new deuteration strategy for assignment and study of large proteins by NMR has been developed and used to characterize one of the largest protein monomer reported to date, human carbonic anhydrase. We have also shown that we can observe the longest range distance constraints to date from NOESY correlations which are important in determining tertiary structure of proteins and we are examining the efficacy of structure determinations based on using these critical but limited constraints.


Maria Anne Schumacher

Nanaline H. Duke Distinguished Professor of Biochemistry

Joseph Heitman

Chair, Department of Molecular Genetics and Microbiology

Joseph Heitman was an undergraduate at the University of Chicago (1980-1984), graduating from the BS-MS program with dual degrees in chemistry and biochemistry with general and special honors. He then matriculated as an MD-PhD student at Cornell and Rockefeller Universities and worked with Peter Model and Norton Zinder on how restriction enzymes recognize specific DNA sequences and how bacteria respond to and repair DNA breaks and nicks. Dr. Heitman moved as an EMBO long-term fellow to the Biocenter in Basel Switzerland where, in studies with Mike Hall and Rao Movva, pioneered the use of yeast as a model for studies of immunosuppressive drug action. Their studies elucidated the central role of FKBP12 in forming complexes with FK506 and rapamycin that inhibit cell signaling and growth, discovered Tor1 and Tor2 as the targets of rapamycin, and contributed to the appreciation that immunosuppressive drugs inhibit signal transduction cascades that are conserved from yeasts to humans.

Dr. Heitman moved to Duke University in 1992, and is a member of the Department of Molecular Genetics and Microbiology where his studies focus on microorganisms addressing fundamental biological questions and unmet medical needs.  Dr. Heitman and colleagues focus on model and pathogenic yeasts including Cryptococcus neoformans and other diverse species from the fungal kingdom. Their studies with fungi as genetic models have revealed biological and genetic principles that can be generalized as models for eukaryotic cell and organism function. These include discovering FKBP12 and Tor1/2 as the targets of the immunosuppressive anti-proliferative natural product rapamycin, elucidating central roles of the calcium activated phosphatase calcineurin governing fungal virulence and morphogenesis and antifungal drug action, deciphering how cells sense and respond to nutrients via permeases, G protein coupled receptors, and the Tor signaling cascade, and illustrating how both model and pathogenic fungi sense both the environment and the infected host. In parallel, their studies address the evolution, structure, and function of fungal mating type loci as models for gene cluster and sex chromosome evolution.  The discovery of an ancestral sex determining locus in the basal fungal lineages involving two HMG domain proteins, SexM and SexP, homologous to the mammalian Sry sex determinant provides insights into both the origins of sex specification and its plasticity throughout the radiation of the fungal and metazoan kingdoms from their last shared common ancestor.  Their discovery of unisexual mating in fungi and subsequent analysis of its impact on the evolution of eukaryotic microbial pathogens provides insights into both microbial evolution and pathogenesis and how sexual reproduction may have first evolved.  Recent studies have unveiled novel mechanisms of antimicrobial drug resistance involving epimutations that silence drug-target genes via RNAi, functions of RNAi in genomic integrity of microbial pathogens, and loss of RNAi in hypervirulent outbreak lineages.

Dr. Heitman is a recipient of the Burroughs Wellcome Scholar Award in Molecular Pathogenic Mycology (1998-2005), the 2002 ASBMB AMGEN award for significant contributions using molecular biology to our understanding of human disease, and the 2003 Squibb Award from the Infectious Diseases Society of America (IDSA) for outstanding contributions to infectious disease research, the 2018 Korsmeyer Award from the American Society for Clinical Investigation, and the 2018 Rhoda Benham Award from the Medical Mycological Society of the Americas.  He is the recipient of an NIH/NIAID MERIT award 2011-2021 in support of studies on fungal unisexual reproduction in microbial pathogen evolution, a Duke University translational research mentoring award in 2012, and a Dean’s Award for Excellence in Mentoring from the Duke Graduate School in 2018.  He has served as an instructor in residence since 1998 for the Molecular Mycology Course at the Marine Biological Laboratory at Woods Hole, MA. Dr. Heitman is an editor for the journals PLOS GeneticsGenetics (2012-2017)PLOS Pathogens (Pearls review editor), Current Genetics (2001-2014)mBio, and Fungal Genetics and Biology; a member of the editorial boards of PLOS BiologyCurrent BiologyCell Host and Microbe, and PeerJ; former editor for PLOS Pathogens (mycology section editor, 2008-2011) and Eukaryotic Cell (2002-2012); an advisory board member for the Fungal Genome Initiative at the Broad Institute, the Fungal Kingdom Genome Project at the Department of Energy Joint Genome Institute, the NIAID Genomic Sequencing Centers for Infectious Diseases, and for the Integrated Microbial Biodiversity Program at the Canadian Institute for Advanced Research (CIFAR); co-chair for the Duke Chancellor’s Science Advisory Council (2009-2010); and co-chair/chair for the FASEB summer conference on Microbial Pathogenesis: Mechanisms of Infectious Disease (2011, 2013).  He was elected a member of the American Society for Clinical Investigation (ASCI) in 2003, a fellow of the Infectious Diseases Society of America (IDSA) in 2003, a fellow of the American Academy of Microbiology in 2004, a fellow of the American Association for the Advancement of Science (AAAS) in 2004, a member of the Association of American Physicians (AAP) in 2006, and a member of the American Academy of Arts & Sciences in 2020.  Dr. Heitman was an investigator with the Howard Hughes Medical Institute from 1992 to 2005. Dr. Heitman served as the director for the Duke University Program in Genetics and Genomics (UPGG) from 2002-2009 (including writing two funded competitive renewals for the T32 NIH training grant and establishing the annual program retreat). He was the founding director for the Center for Microbial Pathogenesis (now called the Center for Host-Microbial Interactions, CHoMI) and served in this capacity January 2002-October 2014.  He is currently the director of the Tri-institutional (Duke, UNC-CH, NC State) Molecular Mycology and Pathogenesis Training Program (MMPTP) (since July 1, 2012), and Chair of the Department of Molecular Genetics and Microbiology (since September 1, 2009).

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