The transmembrane signaling pathway involved in directed movements of Chlamydomonas flagellar membrane glycoproteins involves the dephosphorylation of a 60-kD phosphoprotein that binds to the major flagellar membrane glycoprotein.

Abstract

Abstract. Cross-linking of Chlamydomonas reinhardtii flagellar membrane glycoproteins results in the directed movements of these glycoproteins within the plane of the flagellar membrane. Three carbohydratebinding reagents (FMG-1 monoclonal antibody, FMG-3 monoclonal antibody, concanavalin A) that induce flagellar membrane glycoprotein crosslinking and redistribution also induce the specific dephosphorylation of a 60-kD (pI 4.8-5.0) flagellar phosphoprotein (pp60) that is phosphorylated in vivo on serine. Ethanol treatment of live cells induces a similar specific dephosphorylation of pp60. Affinity adsorption of flagellar 32P-labeled membrane-matrix extracts with the FMG-1 monoclonal antibody and concanavalin A demonstrates that pp60 binds to the 350-kD class of flagellar membrane glycoproteins recognized by the FMG-1 monoclonal antibody. In vitro, protein phosphatase 2B (calcineurin) removes 60% of the 32p from pp60; this correlates well with previous observations that directed flagellar glycoprotein movements are dependent on micromolar calcium in the medium and are inhibited by calcium channel blockers and calmodulin antagonists. The data reported here are consistent with the dephosphorylation of pp60 being a step in the signaling pathway that couples flagellar membrane glycoprotein cross-linking to the directed movements of flagellar membrane glycoproteins. THERE is an emerging view that cell surfaces serve as sensory receptors for motile cells; in particular, cells can detect physical and chemical cues in their environment and respond by activating cytoskeletal machinery that modulates cell adhesion, cell spreading and whole cell locomotion (Lackie, 1986;Singer and Kupfer, 1986;Bray and Hollenbeck, 1988;Stossel, 1989). Contact-induced information transfer across the plasma membrane is thought to be mediated by specific transmembrane glycoproteins (such as integrins) and second messenger pathways often involving protein phosphorylation and dephosphorylation (Damsky and

SMP-1, a Member of a New Family of Small Myristoylated Proteins in Kinetoplastid Parasites, Is Targeted to the Flagellum Membrane inLeishmania

“…Transport of polycistin-2 to the membrane kidney epithelia cilia also appears to occur via an IFT-independent mechanism (Pazour et al, 2002). A calciumdependent process involving flagellar matrix phosphoproteins has been proposed to operate in regulating the directed flow of flagellar membrane proteins in Chlamydomonas reinhardtii (Bloodgood and Salomonsky, 1994) and related proteins could play a role in regulating SMP-1 flagellar localization in Leishmania.…”

Trypanosome IFT mutants provide insight into the motor location for mobility of the flagella connector and flagellar membrane formation

“…How are these membrane proteins transported into the flagellum compartment in the absence of IFT? Studies in Chlamydomonas implicate the flagellum matrix and suggest that a Ca 2+ -dependent mechanism operates to control directed flow of flagellar membrane proteins (Bloodgood and Salomonsky, 1994). However, much still remains to be learnt about this transport pathway and the T. brucei TbCHE2 IFT mutant reported here may provide a model system to study this process.…”

The reciprocal coordination and mechanics of molecular motors in living cells

“…There is only a single flagellar membrane glycoprotein (designated FMG-1) that is in contact with a moving microsphere (4). A number of observations suggest that the cross-linking-induced clustering and movement of FMG-1 within the flagellar membrane is responsible for both gliding motility and microsphere movements (5)(6)(7)(8)(9)). Another bidirectional motility system [called intraflagellar transport (IFT)] operates on the intracellular side of the flagellar membrane (10).…”