Reversible binding and rapid diffusion of proteins in complex with inositol lipids serves to coordinate free movement with spatial information.
Polyphosphoinositol lipids convey spatial information partly by their interactions with cellular proteins within defined domains. However, these interactions are prevented when the lipids' head groups are masked by the recruitment of cytosolic effector proteins, whereas these effectors must also have sufficient mobility to maximize functional interactions. To investigate quantitatively how these conflicting functional needs are optimized, we used different fluorescence recovery after photobleaching techniques to investigate inositol lipid-effector protein kinetics in terms of the real-time dissociation from, and diffusion within, the plasma membrane. We find that the protein-lipid complexes retain a relatively rapid ( approximately 0.1-1 microm(2)/s) diffusion coefficient in the membrane, likely dominated by protein-protein interactions, but the limited time scale (seconds) of these complexes, dictated principally by lipid-protein interactions, limits their range of action to a few microns. Moreover, our data reveal that GAP1(IP4BP), a protein that binds PtdIns(4,5)P(2) and PtdIns(3,4,5)P(3) in vitro with similar affinity, is able to "read" PtdIns(3,4,5)P(3) signals in terms of an elongated residence time at the membrane.
Hammond
Gerald R V
GR
Department of Pharmacology, University of Cambridge, Cambridge, England, UK. gruh2@cam.ac.uk
Sim
Yirong
Y
Lagnado
Leon
L
Irvine
Robin F
RF
D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D036681:Fluorescence Recovery After Photobleaching; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010716:Phosphatidylinositols / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D020703:ras GTPase-Activating Proteins / Q000378:metabolism
D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; C060974:phosphatidylinositol 3,4,5-triphosphate; D020703:ras GTPase-Activating Proteins