Rab27

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RAB27A, member RAS oncogene family
Identifiers
Symbol	RAB27A
HUGO	9766
Entrez	5873
OMIM	603868
RefSeq	NM_004580
UniProt	P51159
Other data
Locus	Chr. 15 q21

RAB27B, member RAS oncogene family
Identifiers
Symbol	RAB27B
HUGO	9767
Entrez	5874
OMIM	603869
RefSeq	NM_004163
UniProt	O00194
Other data
Locus	Chr. 18 q21.2

Rab27 is a member of the Rab subfamily of GTPases. Rab27 is post translationally modified by the addition of two geranylgeranyl groups on the two C-terminal cysteins. Mutations that prevent the expression of Rab27 ('knock out' mutations) cause the hypopigmentation and immunodefficiency disorder known as type II Griscelli syndrome, while a decrease in Rab27 prenylation is thought to be involved in choroideremia.

The symptoms of type II Griscelli syndrome have shown that Rab27 is involved in melanosome transport in melanocytes and in cytotoxic killing activity in cytotoxic T lymphoblasts. In melanocytes Rab27 binds the melanosome. The melanosome is transported along the microtubule. Rab27 then recruits Slac2A and myosin Va, these enzymes are essential for the transfer of the melanosomes from the microtubules to actin filaments. The melanosomes can now continue on their path towards the cell periphery. If either Rab27, Slac2A or myosin Va are absent then the melansomes remain in the perinuclear region of the cell. This disruption in pigmentation results in the hypopigmentation seen in the silvery hair colour of patients with Griscelli syndrome.