How does monoubiquitin turn down Rab5?

Rab5 is monoubiquitinated at specific lysines; ubiquitin at K140/K165 disrupts effector binding and downregulates endocytic trafficking.

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At which lysines is Rab5 monoubiquitinated?

K116, K140, and K165 in HEK 293T and HeLa cells.

What cellular process does Rab5 regulate?

Formation of early endosomes and maturation to late endosomes.

How does monoubiquitination at K140/K165 affect the pathway?

It downregulates the Rab5-mediated endocytic pathway.

Is K116 monoubiquitination critical for localization downregulation?

No—K116 monoubiquitination has no apparent effect on that downregulation.

What happens to mUbRab5 K165 nucleotide handling?

Reduced GDP release and weakened GTP loading.

Why test effector binding after monoubiquitination?

Ubiquitin may sterically clash with Rab5 partners such as GEF/GAP/effectors.

What experimental systems mapped the sites?

Ubiquitination assays in HEK 293T and HeLa cells.

What open question remains about the E3?

The E3 ligase that monoubiquitinates Rab5 is not yet identified here.

What structural approach modeled mUbRab5?

Solution scattering ensemble models of monoubiquitinated Rab5.

What is the paper’s trafficking takeaway?

Site-specific monoubiquitin is an inhibitory signal on Rab5 endocytosis.

Which Rab5 partners were considered in complex models?

Rabex-5 (GEF), RabGAP-5 (GAP), and Rabaptin5.