title: Functional characterization of two RAB27A missense mutations found in Griscelli syndrome type 2.
abstract: Human Griscelli syndrome type 2 (GS-2) is characterized by partial albinism and a severe immunologic disorder as a result of RAB27A mutations. In melanocytes, Rab27A forms a tripartite complex with a specific effector Slac2-a/melanophilin and myosin Va, and the complex regulates melanosome transport. Here, we report a novel homozygous missense mutation of Rab27A, i.e. K22R, in a Persian GS-2 patient and the results of analysis of the impact of the K22R mutation and the previously reported I44T mutation on protein function. Both mutations completely abolish Slac2-a/melanophilin binding activity but they affect the biochemical properties of Rab27A differently. The Rab27A(K22R) mutant lacks the GTP binding ability and exhibits cytosolic localization in melanocytes. By contrast, neither intrinsic GTPase activity nor melanosomal localization of Rab27A is affected by the I44T mutation, but the Rab27A(I44T) mutant is unable to recruit Slac2-a/melanophilin. Interestingly, the two mutations differently affect binding to other Rab27A effectors, Slp2-a, Slp4-a/granuphilin-a, and Munc13-4. The Rab27A(K22R) mutant normally binds Munc13-4, but not Slp2-a or Slp4-a, whereas the Rab27A(I44T) mutant shows reduced binding activity to Slp2-a and Munc13-4 but normally binds Slp4-a.
authors.affiliation: Laboratory of Membrane Trafficking Mechanisms, Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai, Miyagi, Japan.
authors.forename: Norihiko
authors.initials: N
authors.lastname: Ohbayashi
authors.forename: Setareh
authors.initials: S
authors.lastname: Mamishi
authors.forename: Koutaro
authors.initials: K
authors.lastname: Ishibashi
authors.forename: Yuto
authors.initials: Y
authors.lastname: Maruta
authors.forename: Babak
authors.initials: B
authors.lastname: Pourakbari
authors.forename: Banafshe
authors.initials: B
authors.lastname: Tamizifar
authors.forename: Masoud
authors.initials: M
authors.lastname: Mohammadpour
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
authors.forename: Nima
authors.initials: N
authors.lastname: Parvaneh
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000235:genetics* / Q000473:pathology; D020460:Melanosomes / Q000378:metabolism; D050505:Mutant Proteins / Q000378:metabolism; D020125:Mutation, Missense / Q000235:genetics*; D010641:Phenotype; D011485:Protein Binding; D021381:Protein Transport; D013347:Subcellular Fractions / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C492410:MLPH protein, human; D050505:Mutant Proteins; D000075745:rab27 GTP-Binding Proteins; D006160:Guanosine Triphosphate; C066694:RAB27A protein, human; D020691:rab GTP-Binding Proteins