Biochem Blogs

Biochemistry blog, science writing

A new assay to study small GTPase interactions


Let there be {
if  (RhoGTP + Effector == ProteinComplex) {
Luc1 + Luc2 = ActiveLuciferase;
LIGHT = 1; }
else if (RhoGTP + GAP == RhoGDP) {
RhoGDP + Effector = NoProteinComplex;
LIGHT = 0; }
else if (RhoGDP + GEF == RhoGTP) {
RhoGTP + Effector = ProteinComplex;
Luc1 + Luc2 = ActiveLuciferase;
LIGHT = 1; }
LIGHT = 0;
cout << LIGHT << endl;
Clay Clark

Clay Clark

By Clay Clark – @biochemprof

Small GTPases are important for regulation of a host of cellular functions, from gene transcription and other signaling cascades to cell motility, proliferation, and vesicle transport.

In their simplest form, the proteins work as binary switches, where the “on-state” depends on the type of nucleotide bound. For example, with guanosine triphosphate (GTP) bound, the protein forms a conformation that allows it to interact with other proteins (called effectors) that, in turn, convey a molecular signal. In contrast, when the terminal phosphate is hydrolyzed by the GTPase, such that guanosine diphosphate (GDP) is bound, the protein forms a conformation considered the “off-state.” In this form, the protein does not interact with other signaling proteins.

Here’s a short movie that shows a morph between the two nucleotide-bound states of the small GTPase Arf: Arf Conformational Change

The process starts a so-called “molecular clock” in which the amplitude of the signal depends on the length of time GTP is bound to the GTPase because the GTP determines whether the protein is in the “on-state.”

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