The Ras superfamily of GTPases regulate important cellular processes like cell proliferation, differentiation and cell survival, mutations involving the development of cancer. In cancer, apart from the Ras proteins (H-Ras, N-Ras and K-Ras) are also implicated other proteins such as TC21, which shares most of the Ras effectors. TC21 protein may be farnesyl and geranyl, while Ras farnesyl just are.

There is thus a divergence in the nature of the determinants of the association of the GTPases to different systems and membrane microdomains. It may lead to a different subcellular distribution to that exhibited by Ras, an aspect that is unknown. Ras GTPases have two states: inactive, when bound to guanosindifosfato (GDP) and active, are

bound to guanosine triphosphate (GTP). The transition between both states is catalyzed by factor guanine nucleotide exchange (GEF) RasGRF family.

The primary structures reveal that the GEF might be involved in various regulatory mechanisms. We know well the mechanisms that control RasGRF, but knowledge of the activation of TC21 is still scarce. Two scientists from the University of Cantabria have investigated the mechanisms that regulate the activation of TC21 by RasGRF family GEF. They have shown that the GEF can activate TC21 in all Subsites, except in the Golgi complex and that the GEF has a specificity similar TC21 and Ras.

TC21's susceptibility to activation by GEF depends on their posttranslational modifications. In short, they have found similarities and differences of the various structural and spatial determinants that regulate the activity of the GEF against GTPases.

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