3.3.1.2. Ran protein. A Ras nuclear related protein (Ran protein), as
one family of small G protein superfamily, have been widely demonstrated
to be involved in the transport system between cytoplasm
and the nucleus (Wiese et al., 2001). As an important
signal transduction factor, Ran gene encoding ras-related nuclear
protein (Ran protein) was characterized in shrimp. The full length
cDNA is 645 bp, and its genomic DNA has no intron compared with
its cDNA. The Ran protein had the GTP-binding activity. The transcript
and protein of Ran were detected in every tissue of shrimp.
In the WSSV-resistant and WSSV-infected shrimp at 4 h postinfection,
the Ran gene was obviously up-regulated, indicating that
it played a role in shrimp immunity against virus infection (Han
and Zhang, 2007). Through protein interaction approach, it was
found that the PjRan interacted with myosin, a crucial protein in
the process of phagocytosis to form a protein complex. RNAi and
mRNA assays showed that the PjRan could regulate shrimp hemocytic
phagocytosis. Further data evidenced that the depletion of
PjRan by RNAi caused a significant increase of virus copies, and
the overexpression of PjRan resulted in a significant decrease of
virus copies, suggesting that the PjRan participated in the antiviral
immunity by regulating phagocytosis. Therefore, these data revealed
a completely novel aspect of Ran GTPase in phagocytosis
by the direct interaction with the cytoskeleton protein and
presented a novel pathway concerning antiviral immunity, which
contributed to a better understanding of the molecular events in
immune response against virus infection in invertebrates (Liu
et al., 2009d).