Boston University Medical Campus
Medicine

Research in the Biomolecular Medicine Unit is focused on the development of diphtheria toxin-based fusion protein toxins as experimental probes for cellular biochemistry; the genetic and structural analysis of the diphtheria toxin repressor (DtxR); and the structure function relationships of interleukin 7 (IL-7). This work is being done by John Murphy, Ph.D., Chief of the Section of Molecular Medicine, and Professor of Medicine and Microbiology, and Johanna vanderSpek, Ph.D., Research Assistant Professor of Medicine. During the past year, research has focused on the molecular mechanism by which the catalytic domain of DAB389IL-2, a diphtheria toxin-based interleukin-2 receptor targeted fusion protein toxin, is specifically translocated from the lumen of early endosomes to the cytosol of target eukaryotic cells. These studies comprise the doctoral dissertation research of Ryan Ratts, an M.D./Ph.D. student, and have demonstrated that the translocation process is dependent upon a cellular complex of factors that include Hsp90 and thioredoxin reductase.

Additional studies in the Biomolecular Medicine Unit’s laboratory are focused on the elucidation of the molecular mechanism(s) and structural basis by which DtxR undergoes a metal ion-dependent transition from the inactive apo-form to the metal ion-bound active form of the repressor. These studies comprise the doctoral dissertation research of John Love, an M.D./Ph.D. student who has demonstrated that the C-terminal SH3-like domain of the repressor plays a critical role in stabilizing the apo-repressor in its molten globule state. DtxR provides the paradigm for the understanding of metal ion control of virulence gene expression in pathogenic gram-positive bacteria. These studies have provided the first insight into a cooperative role played by the ancillary metal ion-binding site in facilitating metal ion-binding at the primary site in the conversion from the inactive to the active form of the repressor.

Finally, a site-directed mutational analysis of human interleukin-7 has revealed that the indoyl ring of tryptophan 143 plays an essential role in binding to the IL-7 receptor on the eukaryotic cell surface.