Disease relevance of RPH3A

• Abnormal alpha-synuclein interactions with rab3a and rabphilin in diffuse Lewy body disease [1].
• Exophilin A showed antimicrobial activity against Gram-positive bacteria [2].

High impact information on RPH3A

• The core secondary structures are similar to a rabphilin-3A Zn2+-binding domain and to the C1 and LIM domains [3].
• It is proposed to form a novel interface for a Rab11 partner compatible with the simultaneous binding of another partner at the Rabphilin interface [4].
• Therefore, the Rab3-GAP-binding site involves the switch I region of Rab3 and overlaps with the Rabphilin-binding domain [5].
• The membrane association of rabphilin-3A was modestly enhanced in Rab3B-expressing PC12 cells relative to Rab3A-overexpressing cells [6].
• Overexpression of wild-type Rabphilin in the insulin-secreting cell line HIT-T15 did not affect receptor-mediated transferrin endocytosis [7].

Biological context of RPH3A

• Since, alpha-synuclein, rab3a and rabphilin participate in the docking and fusion of synaptic vesicles, it can be suggested that exocytosis of neurotransmitters may be impaired in LB diseases [1].
• Amino acid sequence analysis has revealed that this protein is a bovine counterpart of human beta-adducin which is known to be a good substrate for protein kinase C. The Rabphilin-3A-interacting protein also binds to protein kinase C in the presence of Ca2+ and phosphatidylserine [8].
• We investigated the involvement of Rabphilin in endocytosis using different point mutants of the protein [7].
• Characterization of rabphilin phosphorylation using phospho-specific antibodies [9].
• Rabphilin 3a is a Rab 3-GTP binding protein concentrated on secretory vesicles of neurons and endocrine cells [10].

Anatomical context of RPH3A

• The present study examines alpha-synuclein interactions with rab3a and rabphilin by antibody arrays, immunoprecipitation and pull-down methods in the entorhinal cortex of control cases and in diffuse Lewy body disease (LBD) cases [1].
• In addition to inhibiting exocytosis, constructs containing the NH2 terminus of Rabphilin-3A also perturbed the endocytotic pathway, as indicated by changes in the membrane areas of endosomes, coated vesicles, and the plasma membrane [11].
• The COOH terminus of rabphilin 3A is still capable or substantial enrichment of neurexins from solubilized brain membranes even though only 11 of 33 residues are identical with the COOH terminus of synaptotagmin 1 [12].
• These results suggest that Rabphilin-3A might be involved in the exocytosis of secretory vesicles in hormone-secreting cells as well as in neurons [13].
• Finally, we studied the expression in insulin-secreting cells of rabphilin-3A, a putative effector protein that associates with the GTP-bound form of Rab3A [14].

Associations of RPH3A with chemical compounds

• Identification as beta-adducin of a protein interacting with rabphilin-3A in the presence of Ca2+ and phosphatidylserine [8].
• These results indicate that Rabphilin-3A binds to a protein molecule with a M(r) of 115 kDa through the C2 domain in the presence of phosphatidylserine and Ca2+ [15].
• To identify a Rabphilin-3A-interacting protein, proteins were immunoprecipitated by an anti-Rabphilin-3A polyclonal antibody from the lysate of PC12 cells and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by protein staining [16].
• In this study we demonstrated by a mutation analysis that the polybasic sequence (587 KKAKHKTQIKKK 598) in the C2B domain of rabphilin is required for SNAP-25 binding, and that the Asp residues in the Ca(2+)-binding loop 3 (D628 and D630) of the C2B domain are not required [17].
• Accordingly, significant modification of the secretory responses was observed, at the cell population level, upon transient expression of the serotonin transporter and of proteins known to interfere with exocytosis, such as botulinum neurotoxin C1, GTPase-deficient Rab3 proteins, truncated Rabphilin constructs or Rim [18].

Physical interactions of RPH3A

• These findings corroborate previous observations showing rab3a-rabphilin interactions in control brains, and add substantial information regarding decreased binding of rab3a to rabphilin and increased binding of rab3a to alpha-synuclein aggregates in LB cases [1].
• These results indicate that Rabphilin-3A binds to beta-adducin in the presence of Ca2+ and phosphatidylserine [8].
• However, Rabphilin L83A fails to interact with Rabaptin-5, an important component of the endocytotic machinery [7].

Regulatory relationships of RPH3A

• Rabphilin dissociated from Rab3 promotes endocytosis through interaction with Rabaptin-5 [7].
• Moreover, Rabphilin-3A shows a weak activity to stimulate the GTPase activity of Rab3A and a strong activity to inhibit the Rab3A GTPase-activating protein (GAP)-stimulated GTPase activity of Rab3A [19].

Other interactions of RPH3A

• Rabphilin-3A is a putative target protein for Rab3A small GTP-binding protein implicated in neurotransmitter release [8].
• Rab27a and its rabphilin-like effector protein, Melanophilin, recruit myosin-Va to melanosomes and appear to serve as the membrane receptor [20].
• Furthermore, Rabphilin, a putative target of Rab3, inhibited the activity of Rab3-GAP on Rab3 [5].
• Our data show that immediately after internalization the transferrin receptor and VAMP-2 colocalize on the same vesicular structures, suggesting that Rabphilin favors the rapid recycling of the components of the secretory vesicle [7].
• Our results indicate that Slp2-a, Slp4-a/granuphilin-a and rabphilin are capable of interacting with the plasma membrane directly or indirectly, and thus that these Rab27 effectors form a bridge between Rab27-bound organelles and the plasma membrane [21].

Analytical, diagnostic and therapeutic context of RPH3A

• Immunoprecipitation with rab3a disclosed rab3a binding to rabphilin in control but not in LB cases [1].
• Presynaptic microinjection of recombinant Rabphilin-3A reversibly inhibited the exocytotic release of neurotransmitter [11].

References