Distinct Rab27A binding affinities of Slp2-a and Slac2-a/melanophilin: Hierarchy of Rab27A effectors

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30 Citations (Scopus)


The small GTPase Rab27A has recently been shown to regulate melanosome transport in mammalian skin melanocytes through sequentially interacting with two Rab27A effectors, Slac2-a/melanophilin and Slp2-a. Although Slac2-a and Slp2-a contain a similar N-terminal Rab27A-binding domain (named SHD, Slp homology domain), nothing is known about the functional differences between the Slac2-a SHD and Slp2-a SHD. In this study, the Rab27A-binding affinity of ten putative Rab27A effector proteins has been investigated. It has been found that they could be classified into a low-affinity group (e.g., Slac2-a) and a high-affinity group (e.g., Slp2-a and Slp4-a) based on their Rab27A-binding affinity. Kinetic analysis of the GTP-Rab27A-binding to the SHD of Slp2-a, Slp4-a, and Slac2-a by surface plasmon resonance further indicated that the kinetic parameters of Rab27A for the Slp2-a SHD, Slp4-a SHD, and Slac2-a SHD consisted of a fast association rate constant (3.35 × 104, 2.06 × 104, and 2.11 × 104 M-1 s -1, respectively) and a slow dissociation rate constant (4.48 × 10-4, 3.96 × 10-4, and 2.37 × 10-3 s-1 respectively), and their equilibrium dissociation constants were determined to be 13.4, 19.2, and 112 nM, respectively. Our data suggest that distinct Rab27A binding activities of Slac2-a and Slp2-a ensure the order (or hierarchy) of Rab27A effectors that sequentially function in melanosome transport in melanocytes.

Original languageEnglish
Pages (from-to)666-674
Number of pages9
JournalBiochemical and biophysical research communications
Issue number2
Publication statusPublished - 2006 May 5
Externally publishedYes


  • Griscelli syndrome
  • Melanosome transport
  • Rab-binding domain
  • Rab27A effector
  • Slac2-a/melanophilin
  • Slp2-a
  • Surface plasmon resonance
  • Synaptotagmin

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology


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