CELL BIOLOGY AND METABOLISM BRANCH
Juan Bonifacino, PhD, Chief

The Cell Biology and Metabolism Branch (CBMB) conducts studies on the mechanisms of intracellular protein trafficking and organelle biogenesis, the biology of metal metabolism, the adaptive responses to environmental stresses, and the regulation of the cell cycle during oogenesis. The CBMB's outstanding microscopy facilities permit the use of state-of-the-art techniques such as fluorescent imaging of cells in real time, photobleaching, fluorescence resonance energy transfer, fluorescence correlation spectroscopy, and image analysis in the study of cell structure and dynamics. In addition, the CBMB maintains facilities for cell microinjection and micromanipulation, for automated DNA sequencing, and for work with bacteria, yeast, Drosophila melanogaster, and mammalian cells. Members of CBMB apply knowledge gained from the study of basic cell biological problems to the elucidation of the causes of human diseases, including disorders of lysosome-related organelles, iron overload, and neurodegeneration.
 

Over the past year, the Section on Intracellular Protein Trafficking, led by Juan Bonifacino, discovered critical components of the molecular machinery involved in protein secretion and transport to different compartments within the cell. The group has identified proteins and interactions that determine transport to endosomes and lysosomes, including a novel protein complex that is defective in mouse models of the pigmentation and bleeding disorder Hermansky-Pudlak syndrome. 

The Unit on Protein Biogenesis, led by Ramanujan Hegde, has studied the alterations in the biogenesis of the prion protein (PrP) in the endoplasmic reticulum (ER) that lead to the development of neurodegenerative disease. The group has made significant progress toward a molecular description of PrP translocation, demonstrating how key steps during the process can be modulated to influence the generation of potentially neurotoxic forms of PrP. These advances are beginning to illuminate the entry of secretory and membrane protein substrates into the mammalian secretory pathway. 

Catherine Jackson's group, the Unit on GTPase Regulation of Membrane Traffic, has identified proteins that play important roles in protein trafficking through the Golgi apparatus, in particular binding partners of activators of the Arf GTPase, a central regulator of organelle structure and function. The interactions shed new light on the mechanisms of trafficking through the secretory pathway.
 

The Unit on Cell Cycle Regulation, led by Mary Lilly, has used genetic approaches to identify genes that regulate the cell cycle during gametogenesis in Drosophila, providing unique insights into the poorly understood pathways that drive early meiotic progression and oocyte development in metazoans.

The Section on Organelle Biology, led by Jennifer Lippincott-Schwartz, has continued the development of novel fluorescence imaging tools that promise to revolutionize the analysis of protein dynamics within cells. Some of these tools are variants of the green fluorescent protein (GFP) that show greatly increased fluorescence after activation and allow the analysis of the movement and fate of proteins within the cell. The group is applying the technology to the study of cell division, lysosome biogenesis, and protein secretion.
 

Tracey Rouault's group, the Section on Human Iron Metabolism, studies the regulation of iron metabolism, in particular mechanisms of iron cluster assembly and enzymes and chaperones involved in iron cluster assembly in mitochondria and the cytosol. The group has also analyzed the physiological roles of two iron-regulatory proteins (IRP1 and IRP2) in iron metabolism and in the function of the central nervous system. Defects in IRP2 in mice were found to cause a progressive neurodegenerative disorder.
 

Under the direction of Gisela Storz, the Section on Environmental Gene Regulation studies the mechanisms by which cells defend against oxidative stress. The group conducted analyses of key regulators of the cellular responses to hydrogen peroxide in bacteria and yeast. Another area of research is the identification and characterization of untranslated, regulatory RNAs. Systematic screens for noncoding RNA genes in E. coli have resulted in the identification of 24 new noncoding RNAs.