University of Virginia Health System

The general research program in this laboratory deals with how cells can exhibit directed movements of plasma membrane glycoproteins. In particular, we are studying the role of cytoskeleton-plasma membrane interactions in the movement of plasma membrane glycoproteins responsible for whole cell locomotion. We are using a combined immunological, biochemical and genetic approach to this problem utilizing a model system, the flagellar membrane of the eukaryotic single celled alga, Chlamydomonas. The flagellar surface, as is the case for the general cell surface in mammalian cells, exhibits both sensory and motor properties, which are interconnected by a signaling pathway. Our working model is that the cell surface recognizes contact with a solid substrate, activates a transmembrane signaling pathway which activates intracellular cytoskeletal motors that generate force to move plasma membrane glycoproteins in the plane of the plasma membrane. Movement of plasma membrane proteins that are adherent to the substrate result in whole cell locomotion. Current emphasis in this laboratory is being placed on identifying the transmembrane signaling events whereby multivalent ligand crosslinking of flagellar membrane glycoproteins activates the intra-flagellar machinery for redistributing these proteins in the plane of the flagellar membrane. Crosslinking of a population of 350 kDa flagellar membrane glycoproteins results in a calcium influx across the flagellar membrane and a dramatic dephosphorylation of a flagellar membrane-associated phosphoprotein of 60 kDa and pI of 4.8 which binds to the cytoplasmic domain of the 350 kDa glycoprotein. Thecalcium-activated protein phosphatase 2B (calcineurin) appears to mediate the dephosphorylation of the 60 kDa. Future work will explore the function of the 60 kDa protein in the activation of the flagellar motor machinery responsible for membrane glycoprotein movements. A series of non-gliding mutant cell strains of Chlamydomonas obtained by insertional mutagenesis, are being analyzed in order to shed additional light on the mechanism underlying whole cell locomotion.

Other Websites for this mentor:
http://www.people.virginia.edu/~rab4m/RABResearch/