UMDNJ - ROBERT WOOD JOHNSON MEDICAL SCHOOL
DEPARTMENT OF PATHOLOGY AND LABORATORY MEDICINE

In order to uncover the mechanism that controls membrane fusion in cells, our lab focuses on the conserved protein machinery required for secretory vesicle fusion at the plasma membrane, during exocytosis. Membrane fusion is a mechanism used by biological systems to transfer materials between compartments.  Enveloped viruses, such as influenza virus, HIV and oncogenic retroviruses gain entry into the host cell by fusion of the viral and host cell membranes.  Eukaryotic cells use membrane fusion to transport materials between organelles and to expand the cell surface, for cell growth.  Specialized endocrine cells signal cell proliferation by secretion of growth factors, and neurons communicate by rapid exocytosis of neurotransmitters into the synapse.  In each case, accuracy of material transfer relies on the convergence of multiple factors to stimulate membrane fusion at the correct time and place. 

Structurally similar proteins catalyze both viral and intracellular fusion reactions, presumably using a similar mechanism.  In both cases, in order to become active, the membrane fusion proteins must undergo specific conformational changes.  Whereas much progress has been made in describing the activation of several viral membrane fusion proteins, activation of intracellular fusion proteins, known as SNAREs¹, remains a puzzle. 

In addition to the SNAREs, intracellular membrane fusion reactions require at least a dozen other conserved proteins.  Among these, the Sec1 protein is most likely to activate SNAREs for membrane fusion.  Vesicle fusion is blocked when the Sec1 protein is defective, yet the molecular function of Sec1 proteins is poorly understood.  Our lab uses the genetically and biochemically accessible eukaryote, Saccharomyces cerevisiae to determine the role of Sec1 and other proteins in membrane fusion.  Experiments are designed to isolate functional Sec1 protein, to characterize structurally the binding interaction between the Sec1 protein and SNAREs, and to reconstitute the function of the Sec1 protein in SNARE activation and membrane fusion.  These studies will be extended to other Sec1 homologs to determine whether or not all intracellular membrane fusion reactions require a Sec1 protein and, if so, whether or not the mechanism of action is general or specialized for membrane fusion at distinct compartments in the cell.

The ultimate test of our understanding of the general principles behind vesicle recognition and fusion activation will be the design of a synthetic liposome that recognizes and fuses to a specific target membrane, in response to a fusion signal.  Once that level of understanding is achieved, rationally designed liposomes could become the basis for delivery of therapeutic agents to specific cells.  For example, liposomes could be used to prevent the spread of cancer by delivering to metastatic cells drugs that would inhibit cell growth, or initiate cell death.

¹Soluble N-ethylmaleimide-sensitive factor attachment protein receptor