
TITAN5 は非典型的な小 GTPase であり、高速な GDP/GTP 交換活性と極めて遅いGTP加水分解活性を示す。TITAN5 は細胞内の様々な膜系に動的に局在し、小胞輸送に関与していると考えられる。


coremsg

Small GTPases comprise key proteins in signal transduction that function by conformational switching ability between GDP- and GTP-bound states. The ADP-ribosylation factor (ARF) family is involved in vesicle trafficking and cellular functions. Though evolutionarily well conserved, little is known about ARF and ARF-like GTPases in plants. Here, we characterized functional properties and cellular localization of the essential small ARF-like GTPase TITAN5/HALLIMASCH/ARL2/ARLC1 (hereafter termed TTN5) from Arabidopsis thaliana . TTN5 showed rapid guanine nucleotide exchange capacity comparable to that of human counterparts, but a remarkably low GTP hydrolysis reaction. A TTN5Q70L mutant had enhanced nucleotide exchange activity, indicative of intracellular activation, while TTN5T30N with fast nucleotide dissociation can be considered a dominant-negative form. This suggests that TTN5 is present in GTP-loaded active form in the cells. YFP-tagged TTN5 and the two derived mutant variants were located at multiple sites of the endomembrane system in the epidermis of Arabidopsis seedlings and Nicotiana benthamiana leaves. While YFP-TTN5 and YFP-TTN5Q70L were highly mobile in the cells, mobility was reduced for TTN5T30N. Colocalization with endomembrane markers in combination with pharmacological treatments resolved localization at membrane sites and showed that YFP-TTN5 and YFP-TTN5Q70L were located in Golgi stacks, multivesicular bodies, while this was less the case for YFP-TTN5T30N. On the other hand, all three TTN5 forms were located at the plasma membrane. Hence, the unusual capacity of rapid nucleotide exchange activity of the small ARF-like GTPase TTN5 is linked with cell membrane dynamics, likely associated with vesicle transport pathways in the endomembrane system.

Highlights 

### Competing Interest Statement

The authors have declared no competing interest.

*   Arabidopsis
    :   Arabidopsis thaliana
    ARF-like / ARL
    :   ADP-ribosylation factor-like
    BFA
    :   brefeldin A
    EE
    :   early endosomes
    GAP
    :   GTPase-activating protein
    GEF
    :   guanine nucleotide exchange factor
    ICQ
    :   intensity correlation quotient
    MVB
    :   multivesicular body
    TGN
    :   trans-Golgi network
    TTN5
    :   TITAN 5

Characterization of the small Arabidopsis thaliana GTPase and ADP-ribosylation factor-like 2 protein TITAN5

植物小-gtpase-titan5-の機能特性と細胞内局在の解明


植物小 GTPase TITAN5 の機能特性と細胞内局在の解明
